User Manual XRF 9900

ARL 9900 INTELLIPOWER Series User Manual AA83654

USER MANUAL

ARL 9900 INTELLIPOWER SERIES

AA83654-02

Report MANUAL

No AA83654-02

Language E

Date

August 2007

Department Doc

Author RSc

AA83654-02

The information in this document is subject to change without notice. We assume no responsibility for any errors that may appear in this document.

Die Angaben in diesem Dokument können ohne vorherige Information geändert werden. Wir übernehmen keine Verantwortung für eventuelle Mängel in diesem Dokument.

Les informations contenues dans ce document sont sujettes à changement sans préavis. Nous n’assumons aucune responsabilité pour toutes erreurs éventuelles contenues dans ce document.

Ci riserviamo il diritto di modificare le informazioni contenute nel presente manuale senza preavviso e non ne assumiamo nessuna responsabilità quanto ad eventuali errori che potrebbero esservi accidentalmente introdotti.

Las informaciones contenidas en este documento pueden ser modificadas sin previo aviso. Nosotros declinamos toda responsabilidad sobre los eventuales errores contenidos en este documento.

PAGE DE MODIFICATION

ÄNDERUNGSANGABEN

REVISION CONTROL SHEET

AA83654-02

Date Datum Date

ModificationÄnderung Revision

Description Beschreibung Description

2005

August

2007 August October

00

01 02

Creation of manual Introduction of INTELLIPOWER NEXRD General updating

TABLE OF CONTENTS

Table of Contents

AA83654 ARL 9900 INTELLIPOWER Series User Manual I

1 INTRODUCTION..................................................................................... 1-1

THE ARL 9900 SERIES ...........................................................................................1-1

Front View of the Instrument with the 12 Position Sample Changer ....................1-1

Front View of the Instrument with the X-Y Sample Changer ................................1-2

Front View of the Instrument with Single position Manual loading .......................1-2

View of the Instrument with the X-Y Sample Changer OEM version....................1-3

View of the Instrument integrated for Automation System ARL SMS 900............1-3

X-RAY FLUORESCENCE SPECTROMETER PRINCIPLE .....................................1-4

2 SAFETY.................................................................................................. 2-1

GENERAL WARNINGS............................................................................................2-1

SAFETY DEVICES AND CIRCUITRY......................................................................2-2

Emergency stop push button................................................................................2-3

Restart push button..............................................................................................2-3

X-ray ON lamp .....................................................................................................2-3

Buzzer..................................................................................................................2-4

Interlock safety systems.......................................................................................2-4

3 INSTRUMENT DESCRIPTION ............................................................... 3-1

THE ARL 9900 INTELLIPOWER SERIES INSTRUMENT CONFIGURATIONS......3-1

VIEWS OF THE ARL 9900 INTELLIPOWER SERIES INSTRUMENT.....................3-2

Front view with 12 Position Sample Changer.......................................................3-2

Front View with the X-Y Sample Changer............................................................3-3

Back View of the Instrument.................................................................................3-4

INSTRUMENT DISPLAY..........................................................................................3-6

Spectrometer Status Display................................................................................3-6

X-ray Tube Status Display....................................................................................3-7

Goniometer Status Display...................................................................................3-7

XRD goniometer Status Display...........................................................................3-7

INSIDE THE ARL 9900 INTELLIPOWER SERIES INSTRUMENT ..........................3-8

INSTRUMENT VIEW................................................................................................3-8

Electronic Rack ..................................................................................................3-11

ANALYTICAL CONDITIONS..................................................................................3-13

Table of Contents

ARL 9900 INTELLIPOWER Series User Manual AA83654 II

Goniometer ........................................................................................................3-13 The Universal F45 Goniometer ......................................................................3-13 Configuration table.........................................................................................3-14 The SmartGonio™.........................................................................................3-15 Configuration table.........................................................................................3-15

Compact XRD diffractometer .............................................................................3-16 Unique integrated phase analysis ..................................................................3-16

FULL XRD DIFFRACTOMETER............................................................................3-17

Primary Beam Filter (Option)..............................................................................3-19 List of Primary Beam Filters (Option) .............................................................3-19

FIXED CHANNELS ................................................................................................3-20 Configuration of the monochromators............................................................3-20

ANALYSIS ENVIRONMENT ..................................................................................3-22

Environment Setting...........................................................................................3-22

Gas Regulation (Optional)..................................................................................3-22

Thermal Regulation............................................................................................3-22

SAMPLE EXCITATION ..........................................................................................3-23

X-ray Tube .........................................................................................................3-23

X-ray Power Supply ...........................................................................................3-23

Ecological Mode.................................................................................................3-24

X-ray Tube Safety Interlock................................................................................3-25

X-ray Tube Cooling System for ARL 9900 INTELLIPOWER Series 3600W and 4200W.........................................................................................................3-25

X-ray Tube Cooling System for ARL 9900 INTELLIPOWER Series 1200W 2500W................................................................................................................3-25

SAMPLE HANDLING SYSTEMS ...........................................................................3-26 Manual sample loading ..................................................................................3-26 Sample loading with 12 position sample changer ..........................................3-27 Large X-Y sample changer ............................................................................3-28 Transport belt(s) and docking port .................................................................3-30 Suction option ................................................................................................3-31 Automation.....................................................................................................3-32 Automatic samples.........................................................................................3-32 Manual samples, Setting-up, Control and Type standard samples (SCT) .....3-32 OXSAS / OEM software option ......................................................................3-33

SAMPLE HOLDERS ..............................................................................................3-34

Cassettes ...........................................................................................................3-34

Centring rings.....................................................................................................3-35

Sample supports ................................................................................................3-36

Table of Contents

AA83654 ARL 9900 INTELLIPOWER Series User Manual III

SAMPLE LOADING SYSTEM................................................................................3-37

Sample Loading Process ...................................................................................3-38

4 INSTRUMENT PREPARATION.............................................................. 4-1

SWITCH ON THE INSTRUMENT ............................................................................4-1

With 12 positions cassette magazine ...................................................................4-2

With X-Y magazine ..............................................................................................4-3

SWITCH ON THE PC...............................................................................................4-4

START UP PROCEDURE WITH OXSAS SOFTWARE. ..........................................4-4

Instrument Configuration and Initialisation ...........................................................4-5 Instrument Initialisation ....................................................................................4-5 Perform a goniometer initialisation as described below. ..................................4-6 Gas Supply ......................................................................................................4-6 Environment Setting.........................................................................................4-8 Switch on the XRF X-ray Tube Power Supply................................................4-10 Switch on the Full XRD X-ray Tube Power Supply (applicable on Workstation only) ...........................................................................................4-11 Eco Mode Setting...........................................................................................4-12

INSTRUMENT TECHNICAL DATA ........................................................................4-14

5 SAMPLE PREPARATION ...................................................................... 5-1

Sample Preparation for Solids..............................................................................5-2

Sample Preparation for Powders .........................................................................5-4 Briquet method.................................................................................................5-4 Fusion technique..............................................................................................5-5

Sample Preparation for Liquids ............................................................................5-5 Work-up techniques .........................................................................................5-5

6 ROUTINE ANALYSIS............................................................................. 6-1

CONCENTRATION ANALYSIS WITH OXSAS ........................................................6-1

Performing a Quantitative Analysis in manual mode............................................6-1 With 12 position magazine ...............................................................................6-1 With X-Y magazine cassette version ...............................................................6-2 With X-Y magazine sample version .................................................................6-3

INTENSITY MEASUREMENT WITH OXSAS ..........................................................6-7

QUALITATIVE ANALYSIS WITH SMARTGONIOTM OR UNIVERSAL GONIOMETER AND OXSAS.................................................................................6-10

With 12 position magazine .............................................................................6-10 With X-Y magazine cassette version .............................................................6-11 With X-Y magazine sample version ...............................................................6-12

Table of Contents

ARL 9900 INTELLIPOWER Series User Manual AA83654 IV

QUALITATIVE ANALYSIS WITH COMPACT XRDTM AND OXSAS.......................6-21 With 12 position magazine .............................................................................6-21 With X-Y magazine cassette version .............................................................6-22 With X-Y magazine sample version ...............................................................6-23

Investigating Diffractograms...............................................................................6-28

QUANTITATIVE PHASE ANALYSIS WITH COMPACT XRD CHANNEL ..............6-30

QUALITATIVE ANALYSIS WITH FULL XRDTM AND OXSAS................................6-30 With 12 position magazine .............................................................................6-30 With X-Y magazine cassette version .............................................................6-31 With X-Y magazine sample version ...............................................................6-32

Investigating Diffractograms...............................................................................6-37

QUANTITATIVE PHASE ANALYSIS WITH FULL XRD CHANNEL .......................6-38 With 12 position magazine .............................................................................6-38 With X-Y magazine cassette version .............................................................6-39 With X-Y magazine sample version ...............................................................6-40

Running Visual Crystal .......................................................................................6-42

7 ANALYTICAL ASSISTANT FOR OXSAS .............................................. 7-1

Launching the Online Help...................................................................................7-1

Using the Online Help ..........................................................................................7-2

Navigating the Help session.................................................................................7-2

Printing Help topics ..............................................................................................7-3

About the Analytical Assistant ..............................................................................7-3

To open the Analytical Assistant ..........................................................................7-4

CREATING A METHOD I: BASICS..........................................................................7-5

Defining a Method name ......................................................................................7-5

Defining Concentration ranges.............................................................................7-5

Selecting Elements ..............................................................................................7-6

Adding Elements ..................................................................................................7-6

Setting Sample Preparation parameters ..............................................................7-8

Scan/Energy Profiles............................................................................................7-9

Saving a Method ................................................................................................7-11

Running a Batch.................................................................................................7-12

8 INSTRUMENT CALIBRATION ............................................................... 8-1

INTRODUCTION......................................................................................................8-1

INSTRUMENT CALIBRATION WITH OXSAS..........................................................8-1

Table of Contents

AA83654 ARL 9900 INTELLIPOWER Series User Manual V

9 PERIODIC MAINTENANCE ................................................................... 9-1

SOFTWARE DATA SECURITY ...............................................................................9-1

To backup the database.......................................................................................9-2

To restore a database ..........................................................................................9-5

INSTRUMENT HARDWARE....................................................................................9-7

Sample cassettes.................................................................................................9-7

12 Position Sample Magazine..............................................................................9-7

X-Y magazine trays..............................................................................................9-7

Vane stage pump oil level ....................................................................................9-7

Deionized water level .........................................................................................9-11

Dust filter............................................................................................................9-12

AR-CH4 P10 GAS...................................................................................................9-14

ANALYTICAL PARAMETERS................................................................................9-15

Monochromators ................................................................................................9-15 Energy profiles and detectors resolutions ......................................................9-15

WDS Goniometer ...............................................................................................9-19 Investigate energy profile and detector resolution..........................................9-19

Compact XRD Goniometer.................................................................................9-23 Investigate energy profile and detector resolution..........................................9-23

Full XRD Goniometer for Workstation ................................................................9-25 Investigate energy profile and detector resolution..........................................9-25

Investigate Goniometer scans............................................................................9-27 Principle of Goniometer Positioning ...............................................................9-27 About Position Calibration..............................................................................9-27 Tables of Crystals, Detectors and Collimators combinations .........................9-28 Goniometer F45 Position Calibration Specifications ......................................9-28 Smart GonioTM Position Calibration Specifications.........................................9-30 Compact XRD Position Calibration Specifications .........................................9-31 Full XRD for Workstation Position Calibration Specifications.........................9-32

To perform a scan with WDS goniometer ..........................................................9-33

To perform a scan with Compact XRD goniometer ............................................9-35

To perform a scan with Full XRD goniometer.....................................................9-37

ARL 9900 SERIES INSTRUMENT GLOBAL MAINTENANCE...............................9-39

A APPENDIX A ..........................................................................................A-1

INTRODUCTION..................................................................................................... A-1

X-RAY EMISSION................................................................................................... A-1

Table of Contents

ARL 9900 INTELLIPOWER Series User Manual AA83654 VI

Photoelectric absorption...................................................................................... A-2

Scattering............................................................................................................ A-4

Transmission....................................................................................................... A-5

NOMENCLATURE USED IN XRF........................................................................... A-6

INSTRUMENTATION.............................................................................................. A-7

X-ray Tube .......................................................................................................... A-7 Continuum....................................................................................................... A-8 Characteristic spectra and choice of the X-ray tube target ............................. A-8 Spectral Line Interference............................................................................... A-9 Window thickness ........................................................................................... A-9

DISPERSION ........................................................................................................ A-10

Sequential Instruments ..................................................................................... A-10

Simultaneous Instruments................................................................................. A-11

Instrument Components.................................................................................... A-12 Goniometer ................................................................................................... A-12 Collimators .................................................................................................... A-13

Crystals ............................................................................................................. A-14 Diffraction...................................................................................................... A-14 Multilayer Structures ..................................................................................... A-15 Reflectivity and Resolution............................................................................ A-15 Dispersion Power.......................................................................................... A-16 Stability ......................................................................................................... A-17 Higher orders of diffraction............................................................................ A-17

Resume............................................................................................................. A-18

DETECTION.......................................................................................................... A-19

Gas filled counters ............................................................................................ A-19 Primary Ionization ......................................................................................... A-20 Avalanche ..................................................................................................... A-20 Characteristics .............................................................................................. A-22

Scintillation Counters ........................................................................................ A-23

Pulse Height Discriminator (PHD) ..................................................................... A-24

Final output ....................................................................................................... A-25

1

INTRODUCTION

INTRODUCTION Chapter 1

1 INTRODUCTION

The ARL 9900 Series

X-ray fluorescence allows measurement of up to 84 elements of the periodic table in samples of various forms and nature: solids or liquids, conductive or non-conductive. Typical samples include glasses, plastics, oils, all metals, ores, refractory, cement and geological materials. All samples must not react with the X-rays. The solid samples must support the analysis under vacuum and the liquid samples are analysed under helium environment. Advantages of XRF over other techniques are speed of analysis, generally easy sample preparation, very good stability and precision and wide dynamic range.

The ARL 9900 Series provides high performance measurements on all types of samples. The heart of the ARL 9900 can be made of various modules: monochromators for rapid, dedicated routine analysis, a Moiré fringe Universal or SmartTM goniometer for flexible elemental analysis and an integrated X-ray diffraction system providing a wide range for phase and mineral analysis. The combination of fixed channels and goniometer guarantees speed, flexibility and reliability of analysis.

Four versions are available.

♦ ARL 9900 OASIS is the low power version, with a 1.2 kW generator, without external water cooling. ♦ ARL 9900 INTELLIPOWER is the mid power version, with a 2.5 kW generator, without external water

cooling. ♦ ARL 9900 XP is the standard version, with a 3.6 kW generator. ♦ ARL 9900 XP+ is the high performance version, with a 4.2 kW generator.

Front View of the Instrument with the 12 Position Sample Changer

Figure 1.1

AA83654 ARL 9900 INTELLIPOWER Series User Manual 1-1

Chapter 1 INTRODUCTION

Front View of the Instrument with the X-Y Sample Changer

Figure 1.2

Front View of the Instrument with Single position Manual loading

Figure 1.3

ARL 9900 INTELLIPOWER Series User Manual AA83654 1-2


View of the Instrument with the X-Y Sample Changer OEM version

Figure 1.4

View of the Instrument integrated for Automation System ARL SMS 900

Figure 1.5


Chapter 1 INTRODUCTION

X-ray Fluorescence Spectrometer Principle

The sample to be measured is loaded into the spectrometer and excited by the X-ray beam coming from the X-ray tube: An Incoming x-ray photon strikes an electron, the electron breaks free and leaves the atom.This leaves a void (see next figure).

Figure 1.6

This void is filled by an electron from a higher energy. The electron releases energy (fluoresces) as it drops in the form of an x-ray photon.


Figure 1.7

x-ray photon

The spectrum of the tube is composed of the characteristic wavelengths of the anode elements and the continuum. The emitted radiation from the sample is composed of the tube spectrum and the characteristic wavelengths of the elements in the sample. The reflected beam is guided onto a dispersive system called, in our case, goniometer. This goniometer produces spectra of lines which are in relation with the elements included in the measured sample.

The XRD system collects in its detector the diffracted X-ray of one specific wavelength emitted by the X-ray tube. The incident beam is diffracted by the various crystallographic planes of the crystallites which are present in the sample. For more details about XRD analysis, please refer to the specific brochure about the “ARL 9900 - Integrated XRD system”.


Figure 1.8

All XRF and XRD spectrometers measure intensities. The concentrations are obtained only once the instrument has been calibrated. It should be stressed that an XRF quantometer is a very accurate comparator, but the accuracy of the final analysis is entirely dependent on the quality of the standard samples used for calibration. The intensity concentration relationship is generally linear, but in some cases the curve can be second degree.

C(%) = a0 + a1 * I First degree

C(%) = a0 + a1 * i + a2 * I2 Second degree

Where: i is the intensity measured by the XRF spectrometer aj are the constants computed during the calibration C is the concentration in %

In practice, the intensity of an element is not only a function of the concentration of the element analysed but may also be influenced by interferences such as line overlapping, absorption or enhancement due to constituents of the matrix. The Chapter Analysis Principle gives more information.


2

SAFETY

SAFETY Chapter 2

2 SAFETY

General Warnings

The XRF instrument uses several components, which can be dangerous to manipulate. The signs shown below are stuck to covers and panels etc. to warn you:

Risk of electrocution

Switch off the power before removing this panel or part.

Figure 2.1

Poisonous

Avoid any contact with these components and their support (for example: Beryllium window or TLAP crystal).

Wear gloves when manipulating these components.

Figure 2.2

X-rays

This icon indicates a panel or a part of X-ray shielding.

Switch off the X-ray tube power supply before removing this panel or part.

Figure 2.3

As a general rule the user must contact the nearest local service if he needs to open the instrument.

In case of problem or injury, we will take no responsibility if the user has removed one or several cover or panels fitted with one of the signs shown above.


Chapter 2 SAFETY

Safety devices and circuitry

Figure 2.4 - Instrument

s

Figure 2.5 - Instrumen

ARL 9900 INTELLIPOW2-2

X-Ray On Lamp

with 12 position Magazine

Emergency Stop Button

t with X-Y Sample cha

s

ER Series User

X-Ray On Lamp

nger

Manual

Restart Button

Restart Button
AA83654

SAFETY Chapter 2

X-Ray On Lamps


Figure 2.6 - Instrument with Manual Loading System or Automation System

Emergency stop push button

The emergency stop push button is located on the right front side of the instrument. In case of emergency the red push button is available to shut down the overall electrical power supply of the instrument. The instrument power distribution is protected by a class 4 safety circuit, matching the TUV PTB safety prescriptions. When pressing the emergency stop push button, both the power of the spectrometer and the X-ray tube power supply are switched off.

Important: The computer accessory plug remains live!

Restart push button

The Restart button is located close to the Emergency Stop Button. It allows power-up the instrument.

Pressing the restart push button, the instrument power-up is possible only if:

♦ the emergency stop button is released

♦ the class 4 safety circuit redundancy is fulfilled

♦ the safety circuit power components do not show any defect

X-ray ON lamp

The “X-ray ON” lamps are controlled by the X-ray tube power supply. The lamps are on whenever the X-ray power supply is on. Two bulbs are situated under the cover. If both bulbs are broken the X-ray tube power supply switches off or cannot be switched on.

It is important to use specific bulbs; otherwise there is risk of destroying some electronic parts of the instrument!


Chapter 2 SAFETY


Buzzer

When the X-ray tube power supply is switching on, an internal buzzer is activated for few seconds.

Interlock safety systems

Each component preventing X-ray leaks is secured by a safety switch and is connected to the X-ray tube power supply interlock. All these contacts must be closed to switch on the X-ray power supply. As soon as one part is removed or missing the X-ray power supply switches off immediately.

THE SAFETY CIRCUITS MUST NEVER BE BY-PASSED.

3

INSTRUMENT DESCRIPTION

INSTRUMENT DESCRIPTION Chapter 3


3 INSTRUMENT DESCRIPTION

The ARL 9900 INTELLIPOWER Series instrument requires about 1.5 square meter floor space and is therefore designed to be placed in reduced space areas.

The ARL 9900 INTELLIPOWER Series instrument configurations

3 sample loading systems are available:

12 Positions sample magazine X-Y sample manipulator Single cassette or sample loading

The various acquisition devices are the following:

Number of SmartGonioTM Number of Monochromators

XRD System

Instrument Type

0 32 NO Simultaneous 0 12 YES Simultaneous 1 6 YES Sim / Seq 2 0 YES Sim / Seq

The two, three, four or five displays of the instrument inform the user about the spectrometer status, X-ray tube conditions and the monochromators, goniometer and or diffractometer status with all parameters regarding the measured element or compound line.

The yellow pyramid located on top of the instrument is the “X-ray on” signal. This lamp is illuminated when the X-ray power supply is on. The red button is used to switch off the main power supply in emergency cases, while the green button allows the instrument to be powered.

Chapter 3 INSTRUMENT DESCRIPTION

Views of the ARL 9900 INTELLIPOWER Series Instrument

Front view with 12 Position Sample Changer

1 X-Ray ON lamp

ARL 9900 INTE3-2

1
2 Emergency Stop push-button
3 Restart push-button

4 12 positions cassette loader

5 Loading position

6 Displays

Figure 3.1

5

6

LLIPOWER Serie

2

3

4

s User Manual AA83654


Front View with the X-Y Sample Changer

Figure 3.2

7

5

3 4

AA83654 ARL 9900 INTELLIPOWER S

1

1 X-Ray ON lamp



4 Display

5 X-Y Cassettes / sample loader

6 Right cover (closed)

6

erie

2
7 Left cover (closed)
s User Manual 3-3


Back View of the Instrument

Backside

1 X-Ray ON lamp

Figur

ARL 9900 INTELLIPOW3-4

On the back side of the ARL 9900 INTELLIPOWER Sfeatures are available:

1. The connector for the computer - instrument link (2. Reserved connectors 3. The main breaker (32 A) for the X-ray tube power

Note: With the mid power version (ARL switch, to turn on/off the generator.

4. The main breaker (16 A) for the electronic. 5. Accessory plug dedicated to the computer system. 6. The Master Reset switch. It can be reached with a

4

1

2 Top covers

3 Bottom covers

4 Venting apertures

e 3.3

ER

erie

ACS

sup

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Maxsma

2

5 ACS connector

6 Breakers and accessory plug

3

5

6

Series User Manual AA83654

s instrument, as shown in Figure 3.4 the following

Link).

ply.

0 INTELLIPOWER) this breaker is used like a

imum power current 3.15 A. ll screwdriver; insert it and press.


MASTER RESETACS LINK

SERVI CE LINK

EXTENSI ON I/O

COMPUTER3A MAX MAIN

X-RAYGENERATOR

MASTER RESET

COMPUTER3A MAX

AA83654 ARL 9900 INTELLIPOW

X-RGE

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Figu

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5

1

ACS LINK

SERVICE LINK

EXTENSION I/O

1 ACS connector

2 Reserved connectors

3 32 A Breakers
2
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4 16 A Breakers

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3 4

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5 Accessory plug 3.15 A

6 Master Reset

eries User Manual 3-5


Instrument Display

The ARL 9900 INTELLIPOWER Series instrument is equipped with a display. Three, four or five lines give messages about the spectrometer status, X-ray tube conditions and goniometer status. The next figure shows an example of the display, with one goniometer, one XRD channel, just after switching on the power.

---- STAND BY ----

20 kV 20 mA

90.00 LIF200 C1

PARKED

1

2

3

4

1 Spectrometer and monochromators status

2 X-ray tube status

3 Goniometer 1 status

4 Goniometer 2 / XRD status

Figure 3.5

Spectrometer Status Display

The spectrometer status display shows the state of the ARL 9900 INTELLIPOWER Series instrument. The following list gives the messages and their meanings. Some messages appear simultaneously or alternately on the display.

RESET The spectrometer is being reset.

INIT The spectrometer is being initialized.

NOT CONFIGURED The spectrometer needs to be configured. Configuration data have to be downloaded from the ACS.

STAND BY The spectrometer is ready to analyse.

MEASURE The spectrometer is measuring.

ANA 3 The cassette 3 is in analysis position.

LOAD 3 The cassette 3 is being loaded.

EVAC 3 The cassette 3 is being unloaded.

SEEK 3 The spectrometer is searching for the cassette in position number 3.

F1 The primary beam device 1(filter or collimator) is selected (if this option is fitted).

F2 The primary beam device 2 (filter or collimator) is selected (if this option is fitted).



PUMPING The spectrometer is being pumped down.

VENTING The spectrometer is being vented.

He The Helium environment is selected.

HS : ON The Helium Shutter is on.

HS : OFF The Helium Shutter is off.

WAIT ACO The instrument is waiting for analytical conditions.

The sample rotation is on.




X-ray Tube Status Display

The X-ray tube status display gives the kilovolts and the milliamps of the tube and some other information about the power supply state. The following list gives the messages and their meanings.

RESET The spectrometer is being reset.

60kV 40mA The X-ray tube settings are 60 kV and 40 mA for example.

50->30kV 50->80mA The X-ray tube conditions are changing from 50kV/50mA to 30kV/80mA.

30kV 80mA WAIT TOL The X-ray tube conditions are 30kV/80mA and the spectrometer is waiting to be within the Tolerance.

50->40kV 50->20mA ECO The Eco mode is activated and the X-ray power supply is going to power down to 40kV/20mA. See Eco mode function described in this chapter.

40kV 20mA ECO The Eco mode is activated and the X-ray power supply is in stand by at 40kV/20mA. See Eco mode function described in this chapter.

Goniometer Status Display

The goniometer status display informs the user about the crystal, detector and collimator selection. It also shows the intensity currently being measured.

Some messages can appear simultaneously or alternately on the display.

ZERO REQUIRED The goniometer must be initialised.

CuKα III IIIII IIIII E4 The count rate on the line CuKα is 2.6 104 counts or 26 kcps.

45.03 III IIIII IIIII E4 The count rate on the angle 45.03° is 2.6 104 counts or 26 kcps.

CuKα FPC C4 20s

45.03 FPC C4 20s The angle of the CuKα line is 45.03° and the detector selected is FPC with the fourth collimator (fine). The remaining measuring time is 20 seconds.

CuKα LIF200 C4 20s

45.03 LIF200 C4 20s The angle of the CuKα line is 45.03° and the crystal selected is LiF200 with the fourth collimator (fine). The remaining measuring time is 20 seconds.

Some other messages appear during the zero operation of the goniometer and inform the user about the current operations.

XRD goniometer Status Display

The XRD goniometer status display informs the user about the compound that is presently analysed. It also shows the intensity currently being measured.

Some messages can appear simultaneously or alternately on the display.

ZERO REQUIRED The goniometer must be initialised.

CaO_free III IIIII IIIII E4 The count rate on the line CaO_free is 1.2 104 counts or 12 kcps.

130.75 III IIIII IIIII E4 The count rate on the angle 130.75° is 1.2 104 counts or 12 kcps.

CaO_free 20s

130.75 20s The 2 θ angle for CaO_free line is 130.75° The remaining measuring time is 20 seconds.

Some other messages appear during the zero operation of the goniometer and inform the user about the current operations.


Inside the ARL 9900 INTELLIPOWER Series instrument

Instrument View

This section describes the features and devices located inside the ARL 9900 INTELLIPOWER Series. Some devices are optional and may therefore not be fitted on your instrument.

The following figure shows a general view of the instrument equipped with the SmartGonioTM and MultichromatorsTM.


Figure 3.6

X-ray Tube Vacuum Tank SmartGonio™

The main parts of the instrument are listed bellow:

Spectrometer tank with analytical devices The analytical devices like Fixed Channels, Goniometer, Diffraction System (XRD) and

Primary Beam Devices (PBD) are located in the thermal controlled vacuum tank. The analytical devices are mounted concentric around the sample.

Sample introduction Different sample magazines allow unattended operation, prepare the sample for introduction

into the Primary Chamber and finally move it into the analytical position where sample rotation is possible.

Analytical environment Environment (vacuum or air) in the Spectrometer tank, thermal regulation of the instrument

and the analytical devices, gas regulation for the detectors.

Sample excitation X-ray tube, X-ray tube power supply, X-ray tube cooling system.

Electronic devices Electronic rack and boards, main power connections, power distribution for the main and for

low voltage p.s.

Sample Changer

Molecular Pump

Rotary Vacuum Pump

Sample in Fixed Channels Analysis Position

Primary Beam device

Electronic Module

Water Cooling + Heat Exchanger Generator


The following figure shows a general view of the 9900 INTELLIPOWER Series WORKSTATION equipped with Full Diffractometer Channel.

XRD tube

X’trA optics

XRF tube

Detector

XRD tube

X’trA optics

XRF tube

Detector

Spectrometer tank

Sample changer

Molecular PumpGas regulation

Rotary Pump

ElectronicModule

X-Ray PowerSupply

X-RAYTUBE

CoolingSystem

XRD Tube Rotation

XRD Detector Rotation

X-ray tube

Sampleconveyingsystem

XR

D P

ower

Sup

ply

Figure 3.7



The following figure shows a general view of the instrument equipped with the Full Difractomer and a SmartGonioTM.

XRD tube

Possible configurations:

Number of SmartGonioTM

Number ofUniversal

GoniometerNO NO NO NO 1 NO 2 NO

NO 1 NO 1 NO 2

ARL 993-10

XRD Detector

Figure

s

Number of Monochromators

30 12 6 0 22 14 0

00 INTELLIPOWE

Up to 6 mono or 1 SmartGonio

Up to 6 mono or 1 SmartGonio

3.8

Compact

XRD Full XRD Instrument Type

NO NO Simultaneous NO YES Sim / Seq NO YES Sim / Seq NO YES Seq NO NO Sim / Seq YES NO Sim / Seq NO NO Seq

R Series User Manual AA83654


Electronic Rack

All electronic boards take place in this rack. Figure 3.13 shows the location and the name of each board.

KXx9815D00300

Gon

iom

eter

/XR

D b

oard

1 2 3 4 5 6 7 8 9 10

XPS

: X-R

ay S

petro

met

er p

ower

XGT

: X-r

ay G

as a

nd T

herm

al

XSH

: X-

ray

Sam

ple

Han

dlin

g

o

rXC

M :

X-ra

y C

asse

tte M

agaz

ine

XDI :

X-r

ay D

etec

tor I

nter

face

XQIM

: X

-ray

Qua

ntom

eter

Mas

ter

XSI :

X-ra

y Sa

mpl

e In

trodu

ctio

n

Gon

iom

eter

/XR

D b

oard

8 9 10

XDI :

X-r

ay D

etec

tor I

nter

face

Gon

iom

eter

/XR

D b

oard

8 9 10

XDI :

X-r

ay D

etec

tor I

nter

face

Extentionrack

Extentionrack

Basicrack

Figure 3.9

The XSH board and XCM board are never fitted both together.




1. XSI X-Ray Sample Introduction. This board does control the sample loading from the atmospheric environment to the analytical position and reverse.

2. XQIM X-ray Quantometer Master. This board is the interface with the computer and it manages all sample movements except those done by the sample changer. It drives also the primary beam filter and the programmable aperture changer.

3. XSP This electronic board is the power interface between the XQM and its devices.

4. XGT X-ray Gas and Thermal. This electronic board monitors the FPC gas regulation and the thermal regulation of the spectrometer.

5. Not used 6. XHI X-ray Handling Interface. This electronic board drives the large

sample changer. 7. XCM X-ray Cassette Magazine. This electronic board drives the 12

position sample changer. 8. Not used 9.a XGBI Universal Goniometer

F45 or SmartGonioTM X-ray Goniometer Board. This electronic board drives the goniometer crystal and detector assembly movements, the crystal heating, (the collimator changer, the crystal changer, for Goniometer F45), and generates the detectors high voltage.

9.b XGBD XRD Channel X-ray Goniometer Board. This electronic board drives and controls the goniometer detector assembly movements, the X-Ray tube assembly movements, the crystal heating and generates the detector high voltage.

10. XDI X-ray Detector Interface. This electronic board counts the number of photons received by the goniometer detectors.

11. XMI X-ray Monochromators Interface. These boards are located inside the vacuum tank. They control all activities dedicated to the fixed channels.

Remark: When two or more Goniometers/XRD Channels are installed into the vacuum tank, a special extension electronic rack is added to the basic one at its left hand side. This additional rack does include one XGB/XGBM and one XDI per Goniometer/XRD.


Analytical Conditions

The sample can be measured using different conditions like filters, vacuum environment, different crystals or detectors etc. This section describes these different parts.

Goniometer

The goniometer is the sequential acquisition device of the ARL 9900 INTELLIPOWER Series instrument. The goniometer is a fully automatic, gearless, microprocessor controlled device on which crystals, detectors and collimators are arranged to satisfy Bragg’s law (nλ = 2d sinθ) and to cover the needs of various applications. The two encoder systems ensure fully independent positioning for both the crystal and the detector.

The goniometer is used to perform analyses and scans. Analysis is performed by positioning the crystal at a given Theta and the detector at 2 Theta and counting for certain amount of time. Then the crystal and detector are rotated to a different angle for another line etc. Scanning can be performed by selecting a small angular increment and a short time measuring time per step.

The instrument can be either equipped with the universal F45 Goniometer or with a SmartGonio™.

The Universal F45 Goniometer

The universal goniometer can be fitted with up to nine crystals, one or two detectors and up to four collimators. The figure below shows such a goniometer.

KXx9460D00100

Figure 3.10

1

AA83654 ARL 9900 INTELLIPOWER

1 Collimator changer

2 Crystal changer 2
3 FPC detector
4 SC detector 3

4

Series User Manual 3-13


Configuration table

It is very important to choose the right combination of collimator, crystal and detector for your analysis needs. The following tables will help you doing this:

FEATURE Sensitivity ResolutionK SpectraL SpectraCOLLIMAT.X-Coarse 2.6° V.High LowCoarse 0.6° High FairMedium 0.25° Good GoodFine 0.15° Low HighCRYSTALAXBeB High Low BeAX20 Good Low BAX16 High Low CAX09 Good Low NAX06 High Low OTlAP Good Good OADP Low High MgPET Good Fair AlInSb High High SiGe111 Good High PLiF 200 Good Good KLiF 220 Fair High LiF420 Low V.HighDETECTORFPC ZnScintillation

Ti

Sn...YbCo...Zn…SnHf...U

ElementsBe B C N O -F -Na K Ca...Ti…FeMg Al Si P -S -Cl

Note: The hatched ranges indicate that the application is possible, but not optimum for the concerned elements.



The SmartGonio™

The SmartGonio™ is fitted with three crystals, two detectors and one collimator. The figure below shows a SmartGonio™.

3

14

2

1 SC detector

2 FPC detector

3 Crystal changer

4 Collimator

Figure 3.11

Configuration table

The following table shows the fixed configuration of the SmartGonio™:

Note: The collimator will be selected and installed according to your application.

FEATURE Sensitivity Resolution Elements K Spectra L Spectra

F Na Mg Al Si P S Cl K Ca...Ti…Fe Sn.……..Yb

Co...Zn…Sn Hf……….U

COLLIMATOR

Coarse 0.6° High Fair Medium 0.29° Good Good Fine 0.17° Low High

CRYSTAL AX06 High Low PET Good Fair LiF 200 Good Good

DETECTOR FPC Zn

Scintillation Fe Figure 3.12

Note: The hatched ranges indicate that the application is possible, but not optimum for the elements concerned.



Compact XRD diffractometer

Unique integrated phase analysis

XRF analysis determines the elemental composition of a sample, but mineralogical information is only available through X-ray diffraction (XRD). It permits analysis of the phases or compounds in crystalline materials, e.g. rocks, minerals, oxide products, etc. As an example, XRF only measures the total Ca concentration in a sample, while XRD can give information about the CaO, CaCO3 and Ca(OH)2 contents. Generally, separate XRD equipment is required to obtain qualitative and quantitative structural data. When both types of analysis are required, two separate X-ray instruments should be maintained and operated, which results in significant costs for the user.

The integration of an innovative X-ray diffraction system allows both techniques to be fitted into the same ARL 9900 Series instrument. This patented diffraction system is capable of making qualitative scans and quantitative analysis thanks to its Moiré fringe positioning mechanism. Closely coupled diffraction optics produce very high sensitivity; they offer opportunities for new applications, ensuring a high stability of analysis. Sample alignment problems, common in Diffractometry, are avoided thanks to the accurate sample positioning and focusing beam X-ray geometry. This allows covering a wide 2d range, with an angular range from 85° to 144° with the Compact XRD system.

Separate data sheets are available describing the advantage of such a combined instrument applied to process monitoring in many industries such as cement (Total Cement Analyzer), iron & steel (Total Iron X-ray Analyzer), aluminum (Total Aluminum X-ray Analyzer) as well as other mining processes involving iron ores, limestone, slags, sinters and beach sands among others.

X-RayTube

SamplePrimary BeamDevice

Primary Collimator

Cristal

Detection

Rotation

Motor XRD System

Cassette

Encoder

Figure 3.13



Full XRD diffractometer

The integration of an innovative X-ray diffraction system allows both techniques to be fitted into the same ARL 9900 Series instrument. This patented diffraction system is capable of making qualitative scans and quantitative analysis thanks to its Moiré fringe positioning mechanism. Closely coupled diffraction optics produce very high sensitivity; they offer opportunities for new applications, ensuring a high stability of analysis. Sample alignment problems, common in Diffractometry, are avoided thanks to the accurate sample positioning and focusing beam X-ray geometry. This allows covering a wide 2d range, with an angular range from 10° to 70° with the Full XRD system.

XRD tube

X’trA optics

XRF tube

Detector

XRD tube

X’trA optics

XRF tube

Detector

Sample

Figure 3.14: View of the ARL 9900 Workstation Series

The Diffractograms can be visualised and worked out with OXSAS or with third party software Visual Crystal,...

See example below:



OXSAS Diffractograms.

Figure 3.15

Visual CRYSTALR Diffractograms of a ground sample (rock and clay).

Figure 3.16




Primary Beam Filter (Option)

The primary beam filter (PBF) is inserted between the tube and the sample to modify the X-ray excitation. If XRD channel is not present, four different Primary Beam Filters could be installed on the Primary Beam Device mechanism.

List of Primary Beam Filters (Option)

Filter type Name on the display Use

Cu 0.25mm F1 For analysis of Ru, Rh, Pd, Ag and Cd (elements that are interfered by Rh lines emitted from the X-ray tube Rh anode) in light and variable matrices.

Fe 0.01mm F2 To improve the peak to background ratio of NiKα and CuKα lines.

Al 0.5mm F3 To improve the peak to background ratio of PbLα, PbLß and AsKα, AsKß lines in light matrices.

Be 0.127mm F1 This filter is a protection shield against dust coming from the sample.

(Mainly not used on ARL 9900 INTELLIPOWER Series)


Fixed channels

High-throughput elemental analysis is ensured via fixed channels, each dedicated to the analysis of one element. New, compact slit-crystal geometry has been developed which optimizes the sensitivity and spectral background levels in order to obtain the lowest limits of detection. New detectors ensure a wider linearity of response permitting to reach very high precision levels for major element analysis. Up to 32 monochromators can be fitted in the high power ARL 9900 INTELLIPOWER NEXRD series instruments.

Configuration of the monochromators

The monochromators are fixed assemblies of three elements satisfying BRAGG’s law (nλ = 2d sinθ), a crystal, a detector and a focalization or collimation system. There are two distinct types of monochromators.

Monochromators equipped with focusing crystals:

X-raytube Focussing crystal

Detector slit

Source slit

Primary beam Secondary beamDetector

Sample

Figure 3.17

Natural crystals such as LiF, ADP or PET allow for the utilization of curved crystal focalizing systems of great precision and resolution. These natural crystals ensure excellent analytical results for elements from magnesium atomic number 12 and higher.

The crystals used by Thermo on ARL instruments are curved to a perfectly focusing geometry and aligned on a narrow primary slit thus ensuring very good analysis resolution. The choice of crystal is made according to its reflection capabilities for the wavelength of the element to be analyzed.

Various types of gas detectors or scintillation counters are used according to their measurement efficiency for the wavelength of the element to be analyzed.

Monochromators with curved multilayer crystals and gas sealed detectors are also available for Na and Mg.



Monochromators equipped with flat crystals (Multilayers)


Figure 3.18

The Multilayers are very efficient reflectors for soft X-rays and permit excellent analysis results of light elements from Boron to Magnesium. The physical characteristics of Multilayers, favor the use of flat crystals arrangement equipped with Soller collimators and gas flow detectors (Ar/CH4) with extremely thin windows which are transparent to soft rays.

Primary beam

CrystalX-ray

θ θ 2 θ

Secondary collimator

Primary collimator

Flow proportionalcounter Secondary beam

tube

Sample



Analysis Environment

Environment Setting

Two different modes can be selected, either with a dedicated menu function, or as a step of operation in the unattended analysis mode.

Vacuum This is the environment used for the measurement of all samples that are safe in vacuum (e.g. solids and pressed powders).

Atmosphere This mode does vent the spectrometer tank and is only used for maintenance purpose.

Remark: The typical spectrometer tank pressure in vacuum environment is around 2 Pa (0.00029 PSI)

Gas Regulation (Optional)

The ARL 9900 INTELLIPOWER Series requires one type of gas: Argon-Methane (P10 gas) for the flow proportional counter (FPC). This detector is installed on the goniometer and on some monochromators. The gas regulation system is controlled by the XGT board. In addition to these functions this electronic board drives the venting valve of the tank, checks the vacuum safety in order to prevent any X-ray leaks and controls the thermal stability.

Thermal Regulation

The ARL 9900 INTELLIPOWER Series instruments are designed to provide stable results on long term. To satisfy to this request the instrument must as well show a long term thermal stability. Therefore components which are generating heat have been located into a non thermal controlled area. On the other hand, all the components that need to have a precise thermal stability have been located into a thermal controlled and insulated area.


Sample Excitation

The sample excitation is based on end window X-ray tube which is energised by a solid state power supply. The X-ray tube cooling system is assumed by a water circuit. In order to prevent any problem with the X-rays or high voltage, the instrument is equipped with a safety interlock system.

X-ray Tube

The X-ray tube is positioned at 90° relative to the horizontal plane and the distance between the anode and the sample surface is 30 mm.

The end window design allows a very high sensitivity for light elements and thus low limits of detection. Light element analysis is very efficient with the 75 micron (50 micron optional) beryllium window having a low absorption on light elements wavelengths. The usual target is Rhodium.

PrimaryX-ray beam

X-ray tube

Figure 3.19

X-ray Power Supply

The X-ray power supply is a solid state generator that delivers a maximum power depending of your configuration (1200, 3600 or 4200 Watt).

This unit controls the high voltage and the current applied to the tube. The voltage can be selected by steps of 1 kV. The current can be selected by steps of 1 mA with some restrictions if the voltage selected is lower than 20 kV because it is physically not possible to get for example 0 kV / 120 mA. With the following formula the maximum current according to the desired high voltage can be calculated:

( )2kV5kV26100

4Imax ∗+∗=



Where: Imax is maximum current authorized kV is the desired kilo Volt

Examples: kV desired I maximum kV desired I maximum

0 kV 0 mA 10 kV 30 mA

5 kV 10 mA 25 kV 120 mA

The X-ray power supply can be supplied in different versions.

Instrument Maximum Power

Maximum Voltage

Maximum Emission Current

ARL 9900 INTELLIPOWER

1200W

1.2 kW 60 kV 60 mA


2500W

2.5 kW 60 kV 100 mA


3600W

Standard 3.6 kW 60 kV 120 mA

Option 3.6 kW 70 kV 120 mA ARL 9900

INTELLIPOWER 4200W

Standard 4.2 kW 60 kV 120 mA

Option 4.2 kW 70 kV 140 mA

Ecological Mode

The ecological mode (Eco Mode) is a function which allows you to lower the power consumption and to increase the life time of the X-ray tube.

Warning: It is strongly recommended to never completely switch off the X-ray tube power supply. A frequent shut down and power-up does lead to destruction of the X-ray tube.

When the instrument is idle for a pre-defined time the power is reduced to a stand-by value. For example, if the working condition is 50 kV and 50 mA and the instrument has been idle for 1 hour the power will be reduced to 40 kV and 20 mA in 30 minutes. As soon as the user starts a new measurement the required working condition will be reached automatically.

Another function is available to program the time to raise the X-ray tube to a certain working condition. This can be helpful if the instrument needs to be stabilised before the analysis is started. For example, the X-ray tube is at 40kV/20mA during the night and in the morning it is raised to 50kV/50mA 1 hour before the user arrives in the lab.



X-ray Tube Safety Interlock

All panels or covers with one of the signs shown in Figure 3.20 are controlled by an interlock system. If these panels or covers are not in place, the interlock system will disallow switching on the power on the X-ray tube. We strongly recommend the user to contact our office if the user needs to remove these protections.

High voltage

Radiation

Figure 3.20

Note: This safety interlock operates only on the X-ray tube power supply. The emergency stop button will switch off the instrument main voltage power supply.

X-ray Tube Cooling System for ARL 9900 INTELLIPOWER Series 3600W and 4200W The cooling of the X-ray tube is achieved with an internal closed circuit using de-ionised water, which in turn is cooled through a heat exchanger which uses either tap water or water cooled through a water chiller.

X-ray Tube Cooling System for ARL 9900 INTELLIPOWER Series 1200W 2500W The cooling of the X-ray tube is assured by an internal closed circuit which is cooled through an air-water heat exchanger. Next figure shows the air-water heat exchanger.

1200W 2500W

Figure 3.21



Sample Handling Systems

The sample handling is undertaken by two main devices:

♦ The sample changer. It brings the cassette or the sample holder or onto the lift. ♦ The primary chamber: It serves as an air lock between the atmospheric pressure and the vacuum

environment. The lift brings the cassette into the primary chamber and then the sample is moved in the analysis position.

Three versions of sample loading systems are available:

♦ Manual sample loading ♦ Sample loading with 12 position sample changer ♦ Sample loading with large X-Y sample changer

Manual sample loading

The figure below shows a detailed view of the loading position for an instrument with manual sample loading.

Figure 3.22

Manual loading position



Sample loading with 12 position sample changer

This sample loader (see figure below) is designed to receive up to 12 standard cassettes. The positions of the sample changer are coded and the loading time is minimized thanks to its bi-directional concept.

Figure 3.23



Large X-Y sample changer

This sample loader is a large capacity magazine. It can load standard cassettes and/or it is able to load the samples directly into the ARL 9900 INTELLIPOWER series instrument using special sample supports. Three versions are available:

♦ 98 cassettes for samples of maximum height 30 mm and maximum diameter 52 mm.

Figure 3.24

Tray 100 samples 101..149Tray 0 samples 1..49

Load position

01 7

43 49

101

143 149

107

Cassettes version composed of:

• 2 trays of 49 positions. • 1 clamp for the cassettes.

Figure 3.25



♦ 98 samples which can be loaded directly into the ARL 9900 INTELLIPOWER using special sample supports.

Figure 3.26

Tray 100 samples 101..149Tray 0 samples 1..49

Load position

01 7

43 49

101

143 149

107

Samples version composed of:

• 2 trays of 49 positions. • 1 clamp for the ∅ 57mm support. • Support for the samples families

diameter of: 30.5 to 32mm. 32 to 35 35 to 41 41 to 50 Samples must have parallel faces (+/-2 mm tolerance for 52 mm ∅) See figure 3.28

Figure 3.27



♦ OEM X-Y Sample Loader The OEM (Original Equipment Manufacture) X-Y Sample Loader has been designed in order to connect an ARL 9900 INTELLIPOWER series spectrometer to an automatic sample preparation station generally for pressed powders through transport belt(s). It was conceived and developed for our main OEM Engineering Company customers. These companies integrate the ARL 9900 INTELLIPOWER series instrument with OEM X-Y Sample Loader into their own developed Computer Based Automation Systems for on-line use.

Load position

Baskets positions

Tray 0 samples 1..49

Belts positions

6xx

7xx7xx

7xx

6xx

Waiting positions01 7

43 49

5xx

Belts positions

Load position

Tray 0 samples 1..49Baskets positions

0 1 7

43 49

7xx7xx

7xx

6xx

6xx

Waiting positions

5xx

Figure 3.28

Transport belt(s) and docking port

The OEM X-Y Sample Loader takes samples from a conveyor belt and loads them automatically into the instrument. The samples are generally powders which are pressed into steel rings. A second belt can be installed for unloading samples or to load a second type of samples (e.g. fusion beads).

The docking port accepts one or two conveyor belts of typical 50 to 80 mm width. The belt(s) can be fitted on the loader either to the left front or back, or to the right front or back (see figure 3.27). The belt surface must be positioned at 978 mm from the floor.

Note: If the sample is fetched with the clamp on a belt installed on the left back position, the belt position will show an angle of about 15° relative to the left side of the X-Y loader (see figure 3.27).



Free zone for clampSampleD 68.00

3.00

36.0

0

145.00930.00

970.

00

115.

0033

6.00

145.00

428.

00

144.00 min.Clamp

59.00 min.Suction pad

222.00

978.00 Clamp area

978.00 Suction pad area

222.001220.00

98.00 min.Clamp

183.00 min.Suction pad

9900 OEM X-Y LOADERCLAMP RIGHT, SUCTION PAD LEFT

For suctionpad only

Figure 3.29

Disconnection of the X-Y sample loader from the instrument is required for annual maintenance. Therefore the X-Y loader side apertures are wide enough to permit the belts to stay in there location.

Suction option

This option makes possible the handling of the samples of different diameter coming from belts.

Some restrictions on dimensions of the samples must be taken into account:

34.00..52.00 mm

4.00..25.00 mm

N6

(max. 2mm for diam. 52mm)max. 2.20°

Figure 3.30

The maximum height of the samples used with the trays is 25 mm and their weight should not exceed 200 g.

For other dimensions, the cases must be treated individually through a request for speciality.




Automation

It is important to point out that in each of these systems there is a “Host” Computer supplied by the OEM Engineering Company. This computer is interconnected to the ARL 9900 INTELLIPOWER/OXSAS instrument to direct and control the samples input to the OEM X-Y Sample Loader, the analysis and the output to the transport belt or to classification boxes. The “Host” computer is in general also doing other tasks, like supervising the incoming of material to be analyzed through a pneumatic transport system or driving the automatic preparation machines.

The OXSAS/OEM software option allows interconnection of the OEM software to our OXSAS software. Some development work is required from the OEM part such that their software takes control of our OXSAS software through this interconnection software module. The ARL 9900 INTELLIPOWER/OXSAS with OEM X-Y Sample Loader will function with the direction and control being performed by the “Host” Computer. Consequently we expect that only Engineering Companies or companies with engineering expertise will order an OEM X-Y Sample Loader.

Automatic samples

When loading pressed samples, they must be pressed in Herzog steel rings of diameter 40 mm x height 15 mm or diameter 51.5 mm x height 8.5 mm. On special request, automatic loading of fused beads coming from an automatic fusion unit can be adapted. In this case the fusion bead sample is taken from the belt by a suction device and deposited on an adaptation ring with the analysis face upward. The ring is then carried to the lift of the instrument. In case both types of samples are to be handled the fusion beads must have a smaller diameter than the steel rings. The fusion beads should be sent in advance to the Ecublens factory for evaluation.

Manual samples, Setting-up, Control and Type standard samples (SCT)

The OEM X-Y Sample Loader comprises usually 49 positions (up to 63 on option) for what we call SCT samples (which comprise setting-up samples (SUS), control samples and type standard samples) and for manual loading samples. After analysis these samples are brought back to their original position. Up to 2 waiting positions for automatic unloading to the conveyor belt(s) and up to 3 classification baskets for storing of automatic samples after analysis are available. Access to 49 of the 63 positions for manual loading or setting-up samples is done by opening the corresponding Plexiglas door of the loader and will not stop the automatic loading or unloading of a sample. The manual samples can be powders pressed into steel rings of the same diameter as the automatic samples. If other samples are required to be manually analyzed -for example fused beads or setting-up samples (SUS) - they must be mounted in holders to simulate a steel ring in its external diameter. The available holders can house samples of the following diameters:

• 30.5 mm to 32 mm • 32 mm to 35 mm • 35 mm to 41 mm • 41 mm to 50 mm

In the case when the manual samples have odd shapes or are very thin, special cassettes have been developed to be used in parallel to the automatic samples which are loaded without cassette. The drawback of working with such special cassettes is that the manual sample will be placed further away from the X-ray tube anode due to the thickness of the top of the cassette. Therefore calibration curves have to be adapted with the new geometry specifically for the samples that are analyzed in these cassettes. These cassettes can house samples of diameter max. 52 mm and height of max. 30 mm. They have an opening diameter of 31 mm (while the opening diameter inside the instrument is 29mm – the difference in diameter is such that the analysis devices will not see the edge of the cassette top in the analysis position). For smaller samples, special cassettes with gold or silver coating and opening of small diameter can be used but they can only be ordered with prior agreement of the XRF Product Manager.

A special gripper must be fitted on the X-Y loader with the capability to grab both the sample coming on the belt and these special cassettes.



OXSAS / OEM software option

The full details of the direction and control which must be performed by the Host Computer are described in the ARL Manual P/N AA 83508-02 ARL OXSAS V3.2 “OEM Protocol Description”. This manual covers the messages that must be exchanged between OXSAS and a Host Computer associated with an Automatic System. A chapter of the OXSAS reference manual (Automation option system) describes how OXSAS can be used with such an Automation System -as supplied by one of our Engineering Company customers-. It also describes how to set OXSAS to operate in Automatic Mode and the features that are available when running in this mode.

The OXSAS / OEM software option adds features to OXSAS that allow it to communicate with a Host Computer and to perform the analysis calculations and result distribution without any operator involvement. The message exchanges which are needed between OXSAS and the Host Computer are able to deal with the following cases:

• Production Sample Analysis Messages cover Analytical Task, Sample Identification, Start Analysis

• Return of Sample to Preparation Machine • Setting-Up Sample (SUS) Analysis • Control Sample Analysis • Type Standard Analysis

These messages can be exchanged using a LAN-Local Area Network and the protocol TCP-IP.

In its simplest form the Host Computer can perform the functions and message exchanges dealing only with Production Sample Analysis. In such a case all other operations (drift corrections, SPC by running control samples, type standardization) will have to be performed manually.


Sample holders

Every sample must be placed in a sample holder before it can be introduced into the ARL 9900 INTELLIPOWER Series. The introduction of a sample without the correct holder will stop or damage the sample handling system.

There are two different kinds of sample holders:

♦ Cassettes are used for handling any kind of solid and pressed powder samples. Large cassettes are used with 12 Position Sample Changer. Small cassettes are used with the X-Y sample changer and with the single position loading.

♦ Sample Adapters are used for handling samples without cassettes. 4 different families of sample diameters are defined for the large X-Y sample changer. In case of automation, the centring ring can be adapted to the production sample size and shape.

Cassettes

The standard cassette aperture is ∅ 29 mm and 31 mm. Special coated cassettes with smaller aperture can be obtained on request.

The following picture describes the maximum sample size that can be used with each model of sample changer.

φ 29 mm or φ 31 mm special

φ 52 mm

30 m

m

KXx9880D00100

Sample: maximum dimension

Small cassette

36 m

m

Figure 3.31

Special cassette for Workstation

φ 33 mm special

φ 52 mm

30 m

m

KXx9880D00100


Small cassette

36 m

m

Figure 3.32



φ 29 mmφ 60 mm

40 m

m


Large cassette

50 m

m

Figure 3.33

Special cassette for Workstation

φ 33 mmφ 60 mm

40 m

m


Large cassette

50 m

m

Figure 3.34

Centring rings

In order to insure the sample to be centred, special rings with different diameters are available.

712

φ 36mm

φ 40.5 mm

φ 31mm

17φ 22 mmφ 32 mm

KXx9480D00200 Figure 3.35



Sample supports

With X-Y sample changer where cassettes are not suitable, the samples can be fitted into special sample supports. Depending upon the samples diameter, 4 different supports are available.

For sample diameter ranges of:

♦ 30.5 to 32 mm ♦ 32 to 35 mm ♦ 35 to 41 mm ♦ 41 to 50 mm

Figure 3.36



Sample Loading System

The following figure shows the principle of the sample loading system.

Primary chamber pumping line

Spectrometer pumping line

Shutter motor

Loading lift motor

Analysis lift motor

Sample rotation motor

Cassette and/or sample support

Shell

Shutter

Transfer motor

Figure 3.37

♦ Sample Changer It allows to move or to pick-up the desired cassette or sample support from a dedicated position with a numeric identification

♦ Shutter It serves as an air lock between the atmospheric pressure and the vacuum environment.

♦ Load lift It is the mechanism dedicated to transfer the cassette and/or the sample support from the sample changer into the primary chamber.

♦ Primary chamber It serves as an air lock between the atmospheric pressure and the vacuum environment. The lift drives the sample cassette or sample support into the primary chamber.

♦ Transfer It is the mechanism to move the sample from the loading lift to the analysis lift.

♦ Analysis lift It is the mechanism to raise the sample cassette or sample support to the analysis position under the X-ray tube beam

♦ Sample rotation The sample rotation motor spins the cassette at 30 revolutions per minute during the analysis time in order to average the counts in case the sample is not homogeneous or when the sample presents surfacing grooves.



Sample Loading Process

The ARL 9900 INTELLIPOWER NEXRD Series is designed to analyse solid samples. These samples can be inserted into a cassette or can be put onto a sample support for analysis.

The analysis of the samples is done under vacuum. The sample is first loaded into the primary chamber which is under air. The shutter closes and the primary chamber is pumped down to a low pressure. The sample is then transferred to the spectrometer and raised to the analytical position, as explained hereafter.

♦ Step 1

Next figure shows the instrument ready to load a sample. The sample changer brings the desired sample onto the load lift.

Moving Parts

Washer PartsStructure Parts

AirVacuum


Spectrometer Tank


Figure 3.38



♦ Step 2

The load lift moves the cassette and/or the sample support into the shell (see movement ‘a’).

Moving Parts


AirVacuum


Spectrometer Tank

Spectrometer pumping linea

Figure 3.39

♦ Step 3

The shutter is closed (see movement ‘a’).

Moving Parts


AirVacuum


Spectrometer Tank


a

Figure 3.40



♦ Step 4

The primary chamber is then evacuated to a low pressure by the vane stage pump (see action ‘a’).

Moving Parts


AirVacuum


Spectrometer Tank


a

Figure 3.41

♦ Step 5

When the required vacuum is reached, the lift moves further down pulling the ring down to free the shell (see movement ‘a’).

Moving Parts


AirVacuum


Spectrometer Tank


a

Shell

Ring

Figure 3.42



♦ Step 6

The shell and cassette and/or sample support are moved out of the primary chamber by the transfer mechanism (see movement ‘a’).

Moving Parts


AirVacuum


Spectrometer Tank


a

Figure 3.43

♦ Step 7

The cassette and/or the sample support are then transferred into the spectrometer (see movement ‘a’).


Moving Parts

Washer Parts

Structure Parts Air

Vacuum

Spectrometer Tank

Primarychamber

a

Figure 3.44



♦ Step 8

As soon as the shell is under the analysis position, the analysis lift raises the cassette and/or the sample to the analysis position (see movement ‘a’).


Moving Parts

Washer PartsStructure Parts Air

Vacuum

Spectrometer Tank

Primarychamber

a

Figure 3.45

♦ Step 9 (Sample in Cassette)

The sample is raised to the analysis position by the analysis lift. The sample rotation spins (see movement ‘a’) and the analysis sequence started.


Moving Parts


Vacuum

Spectrometer Tank

Primarychamber

a

Figure 3.46



♦ Step 9 (Sample without Cassette)

Warning: with a 12 position sample conveyor or an X-Y magazine of cassette type, do never load a sample without cassette or with a sample support.

The figure below shows a sample in the analytical position placed on an adapter ring. The spectrometer lift moves the sample up into the analysis position. This movement is controlled by a sensor and therefore allows variable sample thickness. The lift can compensate for a 2 mm non-parallelism of samples.

The sample is raised to the analysis position by the analysis lift. The sample rotation spins (see movement ‘a’) and the analysis sequence started.


Moving Parts


Vacuum

Spectrometer Tank

Primarychamber

Adaptationring

Sample

Ball bearing forsample rotation

Dummycassette

a

Figure 3.47

At the end of the analysis period, the rotation is stopped and the sample cassette or sample support is unloaded following the reverse sequence and driven back to its original position.


4

INSTRUMENT PREPARATION

INSTRUMENT PREPARATION Chapter 4

4 INSTRUMENT PREPARATION

Switch on the Instrument

Note: At this level we assume the ARL 9900 Intellipower Series instrument is properly installed, the main power, the water, gas, serial interface, computer, video terminal and printer are properly connected.

On the back side of the instrument:

1. Switch MAINS breaker on. 2. Switch X-RAY GENERATOR breaker on.

MAST ER RESET ACS LINK

SERVICE LINK

EXTENSI ON I/O

COMPUTER3A MAX MAIN

X-RAYGENERATOR

MASTER RESET ACS LINK

SERVICE LINK

EXTENSION I/O

COMPUTER3A MAX MAIN

X-RAYGENERATOR

KXx9800D01600

1

1 Circuit breaker

Figure 4.1


Chapter 4 INSTRUMENT PREPARATION

With 12 positions cassette magazine

3. On the front of the instrument, turn the red emergency stop button (2) clockwise on. 4. Press the green start button (3)

1 X-Ray ON lamp

Monitor the left upper display. As –NOT COdownloaded from the computer system.

Follow the instruction of the next section.

ARL 9900 INTE4-2

1

4 12 positions cassette loader

5 Loading position

6 Displays

Figure 4.2

5

6

NFIGURED- is dis

LLIPOWER Serie

2

3

4

played, the instrument data need now to be

s User Manual AA83654


With X-Y magazine

3. On the front of the instrument, turn the red emergency stop button (2) clockwise on. 4. Press the green start button (3)

Figure 4.3

7

5

3 4

Monitor the left upper display. As –NOT CONFIGURED-downloaded from the computer system.

Follow the instruction of the next section.

AA83654 ARL 9900 INTELLIPOWER S

1

1 X-Ray ON lamp



4 Display

5 X-Y Cassettes / sample loader

6 Right cover (closed)

6

is dis

erie

2
7 Left cover (closed)
played, the instrument data need now to be

s User Manual 4-3


Switch on the PC

Make sure the computer system is plugged to the main power supply. Switch on the computer unit, the video terminal unit and the printer.

Once Windows XP is started, in the desktop double click on the

icon to start the user interface software.

Start up procedure with OXSAS software.

On the desktop double click on the OXSAS icon to start the software.

Enter the User name and Password

Figure 4.4

In User Name box enter !USER! Leave the Password box empty Click OK

Or

In User Name box enter !MANAGER! Leave the Password box empty Click OK

Important: For security reasons, we strongly recommend to provide real passwords for these default accounts and to create own accounts for your staff with there dedicated passwords. Please refer to the OXSAS online help for more details.



Instrument Configuration and Initialisation

Instrument Initialisation

On the main toolbar select Tools, Actions and Send Instrument Configuration

Figure 4.5

In the next box check High voltage calibration, Position Calibration, Instrument Status and click OK

Figure 4.6

The instrument configuration is now downloaded.

The following information will appear on the instrument display.

STAND BY

kV : 0 mA : 0

ZERO REQUIRED

Figure 4.7

The initialisation of the instrument is done to reset all microprocessors and the mechanical parts. In case of problem with the instrument this operation should be done.



Perform a goniometer initialisation as described below.

On the main toolbar select Tools, Actions and Zero Goniometer

Figure 4.8

Select the goniometer to be initialised

Figure 4.9

Valid the question Are you sure you want to reset the goniometer with OK

The goniometer initialisation process can be monitored on the instrument goniometer display. At the end of the zero process the crystal, detector, collimator, the angular position.

Gas Supply

Argon-Methane Gas for FPC

Check that the gas bottle tap is open. Check that the pressure is set at 0.25 bars on the bottle pressure reducer.

The argon-methane gas flow should be set to 6 ml / min. and the regulation pressure must be 105500 Pa. to be sure the gas regulation system works properly it is recommended to check the gas status.



On the main toolbar select Tools, Actions and read Status

Figure 4.10

In the next window select the gas status.

In the Available Statuses scroll box select the status 1025-FPCpress 1026-FPCFlow and move these parameters to the Selected Statuses scroll box using the >> When the statuses are defined click OK to exit and save.

Figure 4.11

The system will at this point read the selected statuses.



Figure 4.12

If the flow and pressure values are correct, click OK to quit this window.

If the flow and pressure values are not yet reached wait some more minutes and repeat the operation above.

Remark: A 50 litre bottle at 200 bars will last approximately 18 months. Check regularly the gas level of the bottle. To prevent contamination, don’t wait until it gets completely empty before exchanging it.

Environment Setting To select the environment, perform the following actions:

Click on Tools in the main menu. Click on Action. Click on Set X-Ray Chamber Environment. Select Vacuum. Click on OK.

Figure 4.13



The system will start the pumping process. It is possible to monitor the sequences on the XQIM display. At the end of the process the sample loading system is initialised.

The following parameters can be monitored on the ARL Intellipower Series display.

PUMPING PC : > 1000 PA →

0 kV 0 mA OFF

Figure 4.14

PUMPING SP : > 1000 PA ↓

0 kV 0 mA OFF

Figure 4.15

Sign Description ↑ The estimated pressure is increasing ↓ The estimated pressure is decreasing → The estimated pressure is constant

To confirm the vacuum environment is achieved, the ARL 9900 Intellipower Series instrument display must show ‘STAND BY’ in the first display.



Switch on the XRF X-ray Tube Power Supply

Click on Tools in the main menu. Click on Action. Click on Set X-Ray Tube Power.

Figure 4.16

Select On Slow. Select the kV and mA working condition (30 kV and 80 mA for example).

Remark: The condition is depending upon the type of X-Ray tube power supply.

Figure 4.17

Click on OK.

The system will switch on the generator indicating the start with a buzzer and lighting the X-Ray ON bulbs.

The power increase can be monitored on the XSN display.

It is recommended to keep the X-ray tube constantly in operation (24/24 hours) in order to avoid thermal stress on the filament. See Eco mode operation to save energy when the instrument is not in use for analysis.



Switch on the Full XRD X-ray Tube Power Supply (applicable on Workstation only)

Click on Tools in the main menu. Click on Monitoring and Troubleshooting. Click on Monitoring Peripheral Devices. Click on ICS. In the dialog box write XR 45,40,4,1,1 Click Send button

Figure 4.18

Select the kV and mA working condition. 45 kV and 40 mA for example.

Remark: The condition is depending upon the type of X-Ray tube power supply.

The system will switch on the generator indicating the start with a buzzer and lighting the X-Ray ON bulbs.

The power increase can be monitored on the XSN display.

It is recommended to keep the X-ray tube constantly in operation (24/24 hours) in order to avoid thermal stress on the filament. See Eco mode operation to save energy when the instrument is not in use for analysis.



Eco Mode Setting

Eco Mode is a mode in which, when the instrument has not been used for a certain length of time, the X-ray power decreases to a pre-defined power. It is also possible to set the firmware in such a way that the power is raised automatically to specific working conditions at a pre-defined hour on specified dates.

Eco Mode Setting:

Click on Tools in the main menu. Click on Action. Click on Set X-Ray Tube Eco Mode.

Figure 4.19

This causes the dialog box shown in the next figure to be displayed. This dialog box is divided into three parts; the upper part allows definition of the conditions during the Eco mode period. The second part allows definition of the exit time when the Eco Mode has to be left and the X-ray power conditions to which the instrument should return. The third part allows the definition of the exit days, months and years the Eco Mode has to be left or days the eco mode should be kept.



Figure 4.20

Enter Eco Mode Parameters

This allows defining the X-ray power conditions during the Eco Mode and how these conditions should be reached.

Enabled This check box has to be checked to allow the modification of the parameters and to activate the Eco Mode.

kV This is the kV value to be reached in Eco Mode (40 kV is recommended).

mA This is the mA value to be reached in Eco Mode (20 mA is recommended).

Duration to reach the conditions (Minutes) The value entered here defines the time during which the conditions are continuously

changed until the final Eco Mode conditions (kV/mA) are reached. A duration of 60 minutes is the recommended value.

Delay (Minutes) The Eco Mode is started after the instrument has been idle for the time specified here. A

delay of 60 minutes is the recommended value.




Exit Eco Mode Parameters

This allows defining the dates and hour at which the X-ray power conditions should be raised to a specified setting. Furthermore, the way how these conditions should be reached can also be specified.

Enabled This check box has to be checked to modify the parameters and to cause the settings to be activated.

kV This is the kV value to which the X-ray power setting should return when leaving the Eco Mode.

mA This is the mA value to which the X-ray power setting should return when leaving the Eco Mode.

Exit Time (hh:mm) This defines the time of the given dates at which the Eco Mode should be left to reach the

working conditions specified hereafter.

Duration to reach the conditions (Minutes) This value defines the time during which the X-ray power is continuously raised until the

final working conditions (kV/mA) are reached. A duration of 60 minutes is the recommended value.

Delay before re-entering Eco Mode (Minutes) This value defines the delay before the instrument should again return to the Eco Mode in

case the instrument remained idle over the whole period specified here. A delay of 60 minutes is the recommended value.

Select Exit Day(s)

If the date specification should be restricted to certain days of the week on which the Eco Mode should not be left (weekends), then these days can be selected here.

Exit Every Day This check box allows you either to select the day, the month, and the year of eco mode exit,

or to define the days where the eco mode is not exited. If the box is unchecked the exit days month and year are accessible to be defined. In that case the No Exit Days List box is disabled. To the other hand if the box is checked, the day, month, year box is disabled and the No Exit Days List box is enabled, thus allowing the definition of the days where the Eco Mode should not be quit.

No Exit Day List This box allows the definition of the days where the Eco Mode should not be quit. If no day,

in the No Exit Days List should be selected click on “…” at bottom of the list box.

After each modification of one of the parameters described above, the dialog box has to be left by clicking onto the OK button to store the new values.

Instrument technical data

For the instrument technical data, laboratory conditions and safety standards please refer to the ARL Intellipower Series Pre-installation Manual. ARL part number AA83656.

5

SAMPLE PREPARATION

SAMPLE PREPARATION Chapter 5


5 SAMPLE PREPARATION Since X-ray spectrometry is essentially a comparative method of analysis, it is vital that all standards and unknown samples are presented to the spectrometer in a reproducible and identical manner.

The quality of sample preparation in X-ray fluorescence analysis is as important as the quality of measurements.

The preparation method:

♦ Must give specimen with similar physical properties, including mass absorption coefficient, density and particle size, for a certain calibration range;

♦ Must not introduce extra significant systematic errors, for example, the introduction of trace elements from contaminants in a diluents;

♦ Must be rapid and cheap.

Note: For quantitative analysis, samples must be prepared in the same way like the standard samples used for calibration.

An adequately prepared sample:

♦ Must be representative of the material; ♦ Must be homogeneous; ♦ Must, when possible, be thick enough to meet the requirements of an infinitely thick sample.

Various preparation techniques have been described in the literature. The object of this chapter is to point out the main criteria for quality preparation of solid, metallic samples, powder samples, and liquid samples.

The following table shows typical methods of sample preparation.

Type Sample Preparation Purpose Sample holder

Iron Steel Nickel Ferro-Alloy

Cutting

Surface grinding with belt surfacer Surface smoothing Standard cassette

Cu-alloy Al-alloy Pb-alloy

Solid

Zn-alloy

Cutting Surface milling

with lathe Surface smoothing Standard Cassette

Metallic Chemicals Polymer Plant

Grinding Briquetting Equalizing the

density and surface smoothness

Standard Cassette

Ceramic Ore Soil Sediment

Powder

Oxide

Grinding Fusion

Eliminating the mineralogical and the granulometric

differences

Standard Cassette

Chapter 5 SAMPLE PREPARATION


Sample Preparation for Solids

The purpose of preparation is smoothing the surface of the sample. For most analyses, scratch-free surfacing is necessary. For the analysis of light elements, even mirror-like surfaces are often required. For this aim, two polishing methods are applied:

Surface Milling and Lathe: for soft metals; Surface Grinding: for hard alloys and brittle materials such as ceramics.

The difficulty with surface finish is polishing striation. It gives rise to the so-called shielding effect, which results in the decrease of fluorescence intensities. As expected the decrease in intensity is more important for lighter elements when the primary radiation are perpendicular to the striations and weaker when they are parallel to them. For that reason, modern spectrometers are equipped with spinning sample holders to smooth out the influence of sample orientation, resulting in observed intensities on samples and standards that are reproducible.

However, the shielding effect may still be present; sample rotation will compensate for it only if the magnitude of the effect is the same for standards and production samples; this requires that the striation be of the same size and that the sample composition be similar (same effective wavelength).

In the following, we will give some general remarks on the preparation of hard and soft metals.

Soft metals (for example Al, Cu, Mg, Zn or Sn bases)

Striations deeper than few µm may impair significantly the accuracy of determinations. Furthermore, there is a risk of smearing of the softer components: the intensities of the elements in softer phases increase while those of the harder phases decrease.

To obtain the desired surface finish, special precautions must be taken even during milling and especially in the final polishing operation.

Hard metals (for example Fe, Ni, Co bases)

Striation depths of 100 µm are acceptable for elements with characteristic lines of short wavelengths.

To obtain the desired surface finish, fine grits of Al2O3, SiC, B4C (80-180 grits) have to be used. However, polishing may be source of contamination, since currently used abrasives, SiC and Al2O3, contain two elements that are often determined in commercial alloys. In this case, it may be necessary to clean the sample surface to remove these contaminations as well as grease stains and handling residuals.


Shape Melt

Cast

Cool rapidly

Cut to required size:

Casting method

To cassetteor sample stage

Base

Mold

52 mm diam. max.30 mm height max.

Surface

Grinding Milling or lathe

Abrasive paper Grinding stoneCast iron,hard metal

Soft metals,(Al, Cu, Mg, etc

Steels, Co, Ni, etc.

Figure 5.1



Sample Preparation for Powders

The analysis of powder is invariably more complex than that of metallic sample. In addition to interelement interferences and macro scale heterogeneity, particle size effects and mineralogical effects are also important. Although inhomogeneity and particle size can often be minimized by grinding below 50 microns and pelletizing at high pressure, often the effects cannot be completely removed because the harder compounds present in a particular matrix are not broken down. These effects produce systematic errors in the analysis of specific type of material e.g. siliceous compounds in slags, sinters and certain minerals.

Two methods of sample preparation for powders are explained in the following:

Briquet method Fusion technique

Briquet method

The quickest and simplest method of preparation is to press them directly into briquets (or pellets) of constant density. This method can be applied where powders are not affected by particle size limitations. If the self-bonding properties of the powder are good and provided that the powder particles are less than about 50 microns in diameter the sample will pelletize at around 10-30 tons.

Where the self-bonding properties of the powder are poor, higher pressure may have to be employed or in extreme cases a binder will be added before pelletizing.

The binding agent must be chosen with care. It must have the following properties:

Good self-bonding properties Be free from significant contaminant elements Have low absorption. Be stable under vacuum and irradiation conditions Must not introduce significant interelement interferences.

Of the large number of binding agents, which have been successfully employed probably the most useful are wax and methylcellulose.

To cassette orsample stage

Apply pressure

Die

Specimen

Weigh out

Mortar or crusher

Press

Crush, grind and mix

To grain size <50um

Figure 5.2 – Briquet method



Fusion technique

The fusion technique based on the method of Dr F. Claisse is the best way of completely removing both grain size and mineralogical effects. Essentially, the procedure consists in heating a mixture of sample and flux at high temperature (1000°-1200°) so that the flux melts and dissolves the sample. The overall composition and cooling conditions must be such that the end product after cooling is a one-phase glass. Additional advantages are:

Possibility of high or low specimen dilution for the purpose of decreasing matrix effects. Possibility of adding compounds such as heavy absorbers or internal standards to decrease or compensate for matrix effects. Possibility of preparing standards of desired composition.

Heating of the sample-flux mixture is usually done in platinum alloy crucibles but graphite may also be used when conditions permit.

The most frequently used fluxes are borates, namely lithium tetraborate and lithium metaborate or sodium tetraborate. Lithium tetraborate is widely used as it can answer to most cases. In certain cases, mixtures of these fluxes are more effective.

To cassette orsample stage

Weigh outand mix

Flux + Specimen

Heat for Melting

Platinum crucible Remove bubblesGlass diskspecimen

1000° -1100° C

Cast & Cool

Figure 5.3 – Fusion technique

Sample Preparation for Liquids

Work-up techniques

Where the concentration of an element in a sample is too low to allow analysis by one of the methods already described, special techniques have to be used in order to bring the concentration within the detection range of the spectrometer.

Concentration methods

Concentration methods can be employed where sufficiently large quantities of sample are available. For example, gases, airs or waters that are contaminated with solid particles can be treated very simply by two methods:

Filter Method: Drawing the gases, airs or waters through a filter disc followed by direct analysis of the disc in vacuum environment.

Absorption Method: Evaporating the solution directly from a confined spot filter paper.



The following figures show the different preparation methods for liquid samples:

Figure 5.4

Measure under vacuum

Weigh outand mix

Specimen +

precipitant

Agitate andprecipitate

Filtrate

Take out anddry filter

Filter

Filter

Weigh out

Drip and absorb

Dry

Filter

Specimen

Microsyringe

Filter papere.g. Whatman No.40

Filter Method Absorption method


6

ROUTINE ANALYSIS

ROUTINE ANALYSIS Chapter 6

6 ROUTINE ANALYSIS

Concentration Analysis with OXSAS

The concentration analysis is the most frequent task used in process control.

A quantitative analysis is only possible if a method has been created and if the instrument has been calibrated for the quality to be analysed.

Performing a Quantitative Analysis in manual mode

Quantitative analyses can be performed either in manual mode or using the batch utility. This topic describes how to perform a quantitative analysis in manual mode:

Every sample must be placed in a sample holder before it can be introduced into the ARL 9900 Series instrument. The introduction of a sample without the correct holder will stop or damage the sample handling system.

Prior to start a routine analysis, the production samples have to be prepared and must be available. The samples can be fed to the sample conveyor in different manners.

With 12 position magazine

Take the sample and place it into the cassette with the surface to be analyzed down. Place appropriate centring ring.

Sample

Analyzedsurface

Sample

Centringring

Figure 6.1


Chapter 6 ROUTINE ANALYSIS

Move the cover down over the centring ring and twist clockwise until the lock.

Sample

Figure 6.2

Flip the cassette and drop it on the desired numbered position of the 12 position magazine.

With X-Y magazine cassette version


1

2

A

1. Cover 2. Sample prepared surface

down

A: Turn the cover until the stopper

Figure 6.3

Flip the cassette and drop it on the desired numbered position of the X-Y magazine trays.



With X-Y magazine sample version

Take the sample and place it onto the sample support with the surface to be analyzed up.

1

21

2

1. Sample with prepared surface up

2. Sample support

Figure 6.4

Drop the sample support with the sample on the desired numbered position of the X-Y magazine trays.

From the main menu, select Analysis and Data.

Figure 6.5

Then select Quantitative Analysis.



Figure 6.6

The Quantitative Analysis editor opens on the 'Current' tab with the same settings that have been used during the run of the last analysis.

Figure 6.7

If necessary, select the task that you want to use for analysis.

If a default grade, type standard or method is defined in the selected task, OXSAS will automatically select it. Otherwise, select a Grade, Type Standard or Method, according to the type of analysis that you want to perform.



In the Parameter/value grid, enter at least the first Sample ID and the sample position. Enter the value of the manual input, if required.

Click on SID OK to confirm the inputs and to start the analysis. A progression bar indicates the status of the analysis.

Figure 6.8

Note: To save time, it is possible to start the analysis immediately after having entered the sample position by clicking on Start. While the sample is being analyzed the various fields may be completed. When all necessary sample identifier fields have been filled in, click on SID OK.

During a quantitative analysis various checks, as for example a grade check, can be performed by the system. A failure of such a check is indicated by a special background color and a result flag in front of the result value, according to the analysis styles that have been defined in the selected task. Tool tips give further indications on the type of failure.

Figure 6.9



Figure 6.10

The results are processed according to the processing scheme that has been selected in the task. According to the configuration of the scheme, the Manual Processing dialog can be displayed automatically after the execution of an analysis. Otherwise, you can call it any time by clicking on Processing after an analysis is performed in order to process its results.

You can recalculate an analysis result, if necessary.

When a concentration analysis is started, you may be prompted to analyze setting-up samples, type standards or control samples that are out of date. This warning is due to the automatic SCT control.



Intensity Measurement with OXSAS

The measurement of intensities is mainly used to check the reliability and the short and long term reproducibility of the instrument.

The result issued in intensity measurement mode is not subject to drift correction, it is a raw intensity representative of the instrumental response.

Prior to start a routine analysis, the samples have to be prepared and must be available. The samples can be fed to the sample conveyor in different manners, like described in the above section “Performing a Quantitative Analysis in manual mode”.

From the main menu click Operation Setup

Then select Methods

Figure 6.11

In the method pane select New, and under Method enter a new name. It is possible to enter the method description under Description

In the periodic chart click the elements to analyse and click Add Elements.

Click Save to save the method and exit this window to go back to the main menu.

From the main menu select Operation Setup



Click Tasks and Formats

Figure 6.12

In the last column to the right click the upper box at Name level.

Enter the task name and fill the description box.

In the Reproducibility Check Mode select Single Run Analysis.

In the Method / Method select the method name you have created before.

In the Schemes / Sample ID select ARL.

In the Schemes / Element Format you can select Atomic Weight.

In the Schemes / Result Format you can select Intensity.

In the Schemes / Processing you can select Standard.

In Last Calculation Step select RII.

Click Save and OK.

From the main menu click Analysis and Data.



Click Quantitative Analysis.

Figure 6.13

In Task enter the task name defined above.

In Method enter the method name you defined above.

Fill the Parameter and Value grid with a sample name, a sample number and the cassette position number.

Click on SID OK to confirm the inputs and to start the analysis. A progression bar indicates the status of the analysis.



Figure 6.14

At the end of the measurement the results are displayed. They can be printed, transmitted, stored or send to SPC.

Figure 6.15

Remark: From this menu it is possible to measure a New Sample.

Qualitative Analysis with SmartGonioTM or Universal Goniometer and OXSAS

In all XRF instruments equipped with one or more goniometers, it is possible to scan areas of the spectrum to perform qualitative analyses and to verify peak positioning and background positioning. In the case of multi-goniometer instruments, up to 1 XRF goniometer and 1 XRD goniometer systems may be scanned sequentially and recorded. Every sample must be placed in a sample holder before it can be introduced into the ARL NEXRD Series instrument. The introduction of a sample without the correct holder will stop or damage the sample handling system.

Prior to start a routine analysis, the samples have to be prepared and must be available. The samples can be fed to the sample conveyor in different manners.





Sample

Analyzedsurface

Sample

Centringring

Figure 6.16


Sample

Figure 6.17






1

2

A


down


Figure 6.18




1

21

2


2. Sample support

Figure 6.19





Figure 6.20



Then select Qualitative Scans.

Figure 6.21

The Qualitative Analysis editor opens.

Figure 6.22

Select Define/Run Scans.

Alternatively, the dialog can be called from the batch functionality.



Figure 6.23

The dialog contains the following items for scan definition and execution:

Item Description

Scan Name You can select an existing scan name from the drop down list in order to run the scan with the corresponding parameter set or to modify it. Alternatively, enter a new name if a new parameter set is to be created.

Automatic Display Check this box if you want the graphics display to be opened while running the energy profile.

Automatic Peak Identification If this option is selected, OXSAS performs scan identification automatically at the end of the measurement. Furthermore, the peak resolution of the identified peaks and the calculated background will be displayed. The result of this identification will be printed, if one of the print options is selected, together with a list of found peaks.

Description You can enter a free text description.

Lines to Indicate Once you have entered the channel parameters, this option allows selecting element lines that are to be indicated automatically on the scan graphics after the scan has been recorded. Click on the button in order to open the Lines to Indicate dialog.

Result File Enter the path and the name of the file where you want to store the results or browse for it.

Browse If you click on this button, the 'Select Scan Result File Name' dialog opens.



Enter the file name of your choice or select an existing file name and click on Open.

Sample ID Click on the button and select one of the sample identification schemes from the drop down list. The corresponding identifier prompts are displayed in a grid.

Sample Position Select the sample position from the drop down list.

Sample Rotation Check the button if you want to enable the sample rotation.

Note: Sample rotation is only used if the time chosen per step is either 2 seconds or a multiple of 2 so that complete numbers of revolutions are recorded per measured step of the goniometer. For short integration times < 2 seconds, the sample rotation is normally not used, because sample heterogeneity could cause discontinuities in the recorded spectra.

Channel Parameters

Item Description

Channel Type If more than one goniometer is fitted to the instrument, select the XRF or XRD goniometer that will perform the scan.

Crystal Select the Crystal from the list.

Detector Select the Detector from the list (FPC or SC)

2 Theta Angle Start / End Enter the 2 theta start and end angles of the scan range.

Increment Enter an increment between 0.001° and 0.999°. Recommendations

Scan Type Select either Incremental or Fast Digital


Item Description

Counting Time Enter the counting time per step.

Note: For counting times shorter than 2 seconds the sample rotation should be off.

kV / mA Enter the tube conditions.

Primary Beam Filter If Primary Beam filters are fitted, the required filter can be selected here.

Collimator Select a collimator from the list.

Note: The resolution is largely decided by the collimator spacing. Also, natural resolution of the crystals varies, and as general rule the following applies: the better the resolution the smaller the sensitivity. Thus, these two values can be varied somewhat by selecting the appropriate crystal and collimator.

Elliptical mask If Elliptical Masks are fitted, you can select the required Elliptical Mask.



PHD Counting Threshold Intensity threshold below which intensities for steps are not recorded (threshold value is stored).

PHD Threshold / Window PHD threshold and window values are chosen from an energy profile study. The user should decide on a value according to the detector being used for a mid range element. In the case where it is desired to eliminate high order lines, a tight PHD setting should be used.

The allowed range for these values is 0 to 255 with default of 30 for the threshold and 90 for the Window.

Buttons

Start Scan Click on this button in order to start the scan.

Group Scans Click on this button if you want to group several scans before starting them.

Two Theta Calculator Click on this button in order to open the Two Theta Calculator.

Save Click on this button in order to store the current scan definition for later use.

Delete Click on this button if you want to delete the currently selected scan definition.

Figure 6.24

To run a scan:



Prior to running a scan, load the required sample in a cassette and/or put it on the sample loader and specify the sample position.

Define all parameters and settings in the 'Define/Run Scans' dialog.

If you want to group several scans, click on Group Scans.

Figure 6.25

Click on Start Scan. The scan is started. A progression bar indicates the progression of the profile.



To open a spectrum in a new window:



Figure 6.26

Figure 6.27

From the File menu, select Open in New window.... or in the icon bar, click on [icon]. The Open scan dialog box opens. The default folder is defined in the System Preferences dialog.

Select the file(s) that you want to open and click on OK.



Figure 6.28

Identification of the elements present in a spectrum is carried out by finding the element lines corresponding to the various peaks in a spectrum. The information held in this database is used to identify the elements in the spectrum either manually or automatically.

The proposed identifications are tagged with the names of the corresponding element lines and vertical bars indicating the position and the other characteristic of the different lines. On confirming the proposed identifications, the positions of the element lines are then indicated by identification markers and by identification tags.

The software offers three types of peak identification:

• Manual peak identification

• Manual Search Element

• Automatic peak identification

When selecting one of the manual identification methods, the Lines pane opens, allowing defining the identification settings.



Qualitative Analysis with Compact XRDTM and OXSAS

In all XRF instruments equipped with one or more goniometers, it is possible to scan areas of the spectrum to perform qualitative analyses and to verify peak positioning and background positioning. In the case of multi-goniometer instruments, up to 1 XRF goniometer and 1 XRD goniometer systems may be scanned sequentially and recorded. Every sample must be placed in a sample holder before it can be introduced into the ARL 9900 Intellipower Series instrument. The introduction of a sample without the correct holder will stop or damage the sample handling system.



Take the sample and place it into the cassette with the surface to be analyzed down.

Place appropriate centring ring.

Sample

Analyzedsurface

Sample

Centringring

Figure 6.29




Sample

Figure 6.30




1

2

A


down


Figure 6.31






1

21

2


4. Sample support

Figure 6.32



Figure 6.33




Figure 6.34




Figure 6.35




Item Description





Phases to Indicate Once you have entered the Phases parameters, this option allows selecting compounds that are to be indicated automatically on the scan graphics after the scan has been recorded. Click on the button in order to open the Phases to Indicate dialog.


Browse If you click on this button, the 'Select Scan Result File Name' dialog opens. Enter the file name of your choice or select an existing file name and click on Open.







Channel Parameters

Item Description

Phase Type If more than one goniometer is fitted to the instrument, select the XRF, Compact or Full XRD goniometer that will perform the scan.

Crystal Not applicable for XRD Goniometer

Detector Not applicable for XRD Goniometer





Item Description




Collimator Select a collimator from the list only in case of Compact XRD.


PHD Threshold / Window PHD threshold and window values are chosen from an energy profile study. On XRD Goniometer, the detector is measuring a monochromatic radiation.


Buttons







To run a scan:




Figure 6.36

1. Click on Start Scan. The scan is started. A progression bar indicates the progression of the diffraction pattern.



Investigating Diffractograms



Figure 6.37

Then select Investigate Diffractograms.

From the File menu, select Open in New window.... or in the icon bar, click on [icon]. The Open scan dialog box opens. The default folder is defined in the

dialog.System Preferences


Figure 6.38




Identification of the Phases present in a Diffractogram is carried out by finding the phases corresponding to the various peaks of the Diffractogram. The information held in this database is used to identify the Phases in the Diffractogram either manually or automatically.

The proposed identifications are tagged with the names of the corresponding phases and vertical bars indicating the position and the other characteristic of the different phases. On confirming the proposed identifications, the positions of the phases are then indicated by identification markers and by identification tags.

The phase identification is related to the concept of the reflection, h, k & l associated to the name of the Phase, as Miller Indices (e.g. CaCO3-1 0 4).


Quantitative Phase Analysis with Compact XRD channel

Follow the same procedure as for a Concentration Analysis with OXSAS described at the beginning of this section. The difference is that instead of XRF Lines for elementary analysis, compounds have to be inserted into the Method.

Qualitative Analysis with Full XRDTM and OXSAS





Sample

Analyzedsurface

Sample

Centringring

Figure 6.39




Sample

Figure 6.40




1

2

A


down


Figure 6.41






1

21

2


2. Sample support

Figure 6.42



Figure 6.43




Figure 6.44




Figure 6.45




Item Description





Phases to Indicate Once you have entered the Phases parameters, this option allows selecting compounds that are to be indicated automatically on the scan graphics after the scan has been recorded. Click on the button in order to open the Phases to Indicate dialog.


Browse If you click on this button, the 'Select Scan Result File Name' dialog opens. Enter the file name of your choice or select an existing file name and click on Open.





Channel Parameters

Item Description

Phase Type If more than one goniometer is fitted to the instrument, select the XRF, Compact or Full XRD goniometer that will perform the scan.

Crystal Not applicable for XRD Goniometer

Detector Not applicable for XRD Goniometer







Item Description




Collimator Select a collimator from the list only in case of Compact XRD.


PHD Threshold / Window PHD threshold and window values are chosen from an energy profile study. On XRD Goniometer, the detector is measuring a monochromatic radiation.


Buttons







To run a scan:




Figure 6.46

Click on Start Scan. The scan is started. A progression bar indicates the progression of the diffraction pattern.



Investigating Diffractograms



Figure 6.47


From the File menu, select Open in New window.... or in the icon bar, click on File icon. The Open scan dialog box opens. The default folder is defined in the System Preferences dialog.


Figure 6.48

Identification of the Phases present in a Diffractogram is carried out by finding the phases corresponding to the various peaks of the Diffractogram. The information held in this database is used to identify the Phases in the Diffractogram either manually or automatically.

The proposed identifications are tagged with the names of the corresponding phases and vertical bars indicating the position and the other characteristic of the different phases. On confirming the proposed identifications, the positions of the phases are then indicated by identification markers and by identification tags.

The phase identification is related to the concept of the reflection, h, k & l associated to the name of the Phase, as Miller Indices (e.g. CaCO3-1 0 4).



Quantitative Phase Analysis with Full XRD channel

With the ARL 9900 Workstation Series, with full integrated Diffractometer, an additive facility has been integrated, providing quantitative phase analysis from Diffractograms acquired with OXSAS. In such a case, third party software is used providing the appropriate algorithms to match intensities with phases concentrations.

In OXSAS software define the qualitative scans parameters and run the qualitative scan





Sample

Analyzedsurface

Sample

Centringring

Figure 6.49




Sample

Figure 6.50




1

2

A

1 Cover 2 Sample prepared surface

down


Figure 6.51






1

21

2

1 Sample with prepared surface up

2 Sample support

Figure 6.52


OXSAS offers two ways to perform the Phase Quantitative Analysis.


Figure 6.53




Figure 6.54




Figure 6.55



Running Visual Crystal

On the Desktop of the PC double click the Visual Crystal Icon

Figure 6.56

Enter Username and Password

Click OK

Figure 6.57

Run Sentinelle

Click the Sentinelle Radio Button

Figure 6.58



In OXSAS


1 Then select Qualitative Scans.

Figure 6.59


From the File menu, select Open in New window.... or in the icon bar, click on File icon. The Open scan dialog box opens. The default folder is defined in the System Preferences dialog.

Select the file that you want to open and click on OK.

Figure 6.60



In the tool bar select Math

and Quantify XRD Phases

Figure 6.61

OXSAS prompts the user to select the dedicated Method defined in Visual Chrystal.

Select the Result data file name and path.

Figure 6.62



Once the Method and path are selected click OK

The system will compute the dedicated Phases concentrations and display the results in the OXSAS Quantitative Analysis menu.

Figure 6.63



2 From the Operation Setup menu

Select Method

Create a Method

Select the thumbnail Method Header

Figure 6.64

In the Result Display box:

Define the result format to be used.

In XRD Quantification box:

In the Scan Parameters scroll menu select the scan parameters.

In the Quantification Method select the Visual Crystal (Macro in Visual Chrystal) method.

Specify the Quantification Result Filename and path to save the results.

In the Methods window:

Click Save button to save the current method.

Put the sample to be analysed in the proper cassette and position.



In Analysis and Data:

Select Quantitative Analysis

Figure 6.65

In the Task scroll box:

Select ARL

In the Method scroll box:

Select the task defined above (XRD-Full Only)

In the Sample ID box enter the Sample Name, N°, Runs, Position.

Click SID Ok + Start button.

The system does execute the predefined scan and compute the phases concentrations.

The final results are displayed in the OXSAS Quantitative Results window.



Figure 6.66


7

ANALYTICAL ASSISTANT

Analytical Assistant Chapter 7

7 ANALYTICAL ASSISTANT FOR OXSAS For customers who own the OXSAS software as user interface, an Online Help is available.

This Online help does lead the user through the different facilities implemented in OXSAS to perform analytical tasks, calibration, process control, etc.

Prior to start to use the analytical assistant the Online Help has to be launched.

Launching the Online Help

OXSAS is supplied with an integrated Online Help.

To launch the Online Help: • From the main menu, select Help - Help. The help opens on the 'Welcome' page.

Figure 7.1

OR • From any dialog in OXSAS, press the F1 key. The help opens directly on the page that concerns the

dialog for which you have requested help. To get the maximum benefit from the Online Help, it is good to familiarize yourself with the different ways to use the help to get answers to your questions.

Note: There is no printed user manual for this product. The contents you might look for in a user guide book, as for example, explanations, descriptions and procedures are included in the Online Help. However, you can print individual Help topics.


Chapter 7 Analytical Assistant


Using the Online Help

Basically, the Online Help has been designed to be context-sensitive. This means that when pressing the F1 key from any dialog of the software, you would call the appropriate help topic.

However, the Online Help contains several features that help you becoming familiar with OXSAS and finding information on a special subject:

Contents tab: Basically, the order of help topics follows the OXSAS menu structure. To open a book, click on its title or on the + sign to the left of the book. A book contains either further books or help topics. To show the content of a help topic, click on the corresponding title.

Shortcuts for navigating in the table of contents:

Shortcut Description

Enter Open the selected item.

Up and Down arrows

Select the previous or next element.

Left and Right arrows

Expand or collapse the selected item.

Search tab: This tab allows searching for a special keyword. As a result, a list of topics containing the keyword to find is displayed. To display a topic from the list, double-click on it or select it and click on Display.

Note: You cannot use Boolean operators (such as AND, OR, NOT, or quotation marks) to limit or refine your search of Help. If you type more than one word, the search results include every topic in which at least one of your search words appears.

Browse Sequences: The Online Help contains several browse sequences that serve as tutorials. You will find step-by-step procedures for accomplishing different tasks with OXSAS.

Navigating the Help session

The Help system maintains a history of your Help session so that you can go back and forth quickly among the topics you open.

• You can use the 'Back' arrow button on the Help toolbar to return to topics you opened earlier in your Help session.

• Right-click anywhere in a topic. A contextual menu opens. Click on Back to return to topics you opened earlier in your Help session. Click on Forward to move forward again in your Help session history.

When you close the Help, you end your Help session. This deletes your Help history.



Printing Help topics

You can print any individual topic from the Online Help.

Each topic must be printed individually. You cannot print multiple topics at a time or entire help sections from the Help window.

To print a Help topic: 1. Open the Help topic that you want to print.

2. In the Help toolbar, click on Print.

OR

Right-click anywhere in the topic to open the contextual menu and select Print.... The 'Print' dialog opens, allowing selection of a printer and the number of copies.

3. Click on Print in order to start printing.

About the Analytical Assistant

The Analytical Assistant is based on a Knowledge Table (currently only available for the XRF instruments) that contains the analytical parameters that are best suited for the instrument.

The Analytical Assistant can be used for creating a method. If used, you simply define the elements you need to analyze from a periodic table, their chemical form, their concentration range and additional information related to the preparation of the sample. OXSAS proposes, in turn, the most suitable spectral line with the corresponding analytical parameters for analyzing a chemical element with regard to sensitivity, choice of elements and possible line overlaps.

Furthermore, the Analytical Assistant provides a list of potential problems and an indication on how these can be solved to quickly check the set-up of lines with a typical sample using scans, to check line overlaps and the sensitivities, and energy profiles to check higher order overlaps.


To open the Analytical Assistant

In the Online Help window select Creating a Method I: Basics.

In this window the Analytical Assistant can be accessed. Click on Analytical Assistant

Figure 7.2

Figure 7.3

Follow the instruction of the Help Online flow chart. Start to define the first Method.



Creating a Method I: Basics

Figure 7.4

Defining a Method name

The first step in creating a method is entering a method name.

There are two ways to enter a method name:

1. On the Method pane, click on New. A new row is added to the grid. In the 'Method' field, a default name (newMethod) is displayed.

OR

Scroll down to the end of the list and select the last row.

2. Enter the method name of your choice and a description. On the 'Periodic Table' tab, the Analytical Assistant is opened, indicating the next steps for creating a method.

3. Select an existing category from the drop down list or enter a new category.

Next step:

• Defining concentration ranges.

Defining Concentration ranges

Three concentration ranges can be specified for each element in order to refine the solving procedures for potential overlap problems.

The following levels are available:

• Major (>10 %)

• Minor (0.5 - 10 %)

• Traces (<0.5 %)

To define a concentration range:

1. Click on one of the range buttons (Major, Minor or Traces).

2. Click on the desired element(s). The selected range will be applied to all elements that you select until you click on another range button.

3. Repeat the procedure for other ranges.




Note 1 : By default, 'Minor' is selected.

Note 2 : The indicated percentage levels should not be taken too strictly. Especially selecting elements as Majors will influence strongly the choice of instrumental parameters to reduce the sensitivity of the element line. The selection of the instrumental parameters is done in such a way that the detection system will not be saturated.

See Also: Saturation Flags.

Selecting Elements

The Periodic Table tab allows selecting elements to be included to the method.

To select an element:

• Click on the corresponding chemical symbol in the periodic table. The font color of the selected element will change to red italic, blue italic or green italic, depending on the selected concentration range.

Note : By default, Minor is selected as concentration range.

To remove an element selection:

• Click on the selected chemical.

Next step:

• Adding elements

Adding Elements

Once you have selected the elements that you want to measure with the method and defined the concentration ranges, you have to add the elements to the method.

Note : This function can also be used for adding elements to an existing method.

To add elements to the methods:

1. On the 'Periodic Table' tab, click on Add Elements. The 'Add Analytical Assistant Components' dialog is displayed. It shows the analytical and instrumental parameters that are proposed by the Analytical Assistant for the selected elements. The upper grid contains the elements and their parameters on the goniometer, the lower grid contains the selected elements which can also be analyzed with a monochromator and their parameters.

Note : The selection criteria applied in this process are explained in Details about the Selection Criteria.

2. Prior to confirming the settings you can do one of the following:

• Set sample preparation parameters.

• Adapt parameters and/or analytical conditions that are proposed by the Analytical Assistant.

3. If you have done any modifications in this dialog, click on Apply changes in order to apply them.



4. Click on OK. The elements are added to the method. The dialog is closed and you return to the Method editor. The elements that have been added are now displayed in bold, the color still indicating the selected concentration range.

In detail, the grids contain the following items:

Item Description

Check box Enable the check box of the components that you want to measure, either on the goniometer, on a monochromator or on both.

Element Name of the selected element. The concentration range is indicated by the font color.

Transition The element line that will be measured. If you select another line, the crystal is changed accordingly, if necessary and vice versa.

Description Select whether it is an analyte or an overlapping element

Component Type

kV / mA The proposed tube conditions are chosen according to the selected elements:

• 30 kV / 80 mA if only elements from Be to Fe (included) are present

• 60 kV / 40 mA if only elements from Ti to Cf (included) are present

• 50 kV / 50 mA in all other cases.

Crystal / Detector / (PBF Filter) / Collimator

The selection is done according to the Knowledge Table. However, the settings can be changed.

Counting Time The selection is done according to the Knowledge Table. However, the settings can be changed.

PHD Threshold / Window The selection is done according to the Knowledge Table. However, the settings can be changed.

Note : After the overlap investigations have been completed, it may be necessary to adjust the PHD

settings and to choose different instrumental parameters, like a finer collimator. Changes to these values will then be done on the Components tab.

Furthermore, the dialog contains the following buttons:

Button Description

Sample preparation If you want to define details on the sample preparation of the major element, click on this button. The Sample Preparation dialog opens.

Apply changes You can change the settings that are proposed by the analytical assistant. Click on this button in order to apply them.

OK Confirm the settings and quit the Analytical Assistant.



Cancel Quit the Analytical Assistant without saving.

Info Open the Information dialog.

Overlaps Open the Overlaps dialog.

To choose whether a measurement is performed on the goniometer, on a monochromator or on both:

• Check the corresponding box in the first column of the corresponding grid.

Setting Sample Preparation parameters

Important: This button is enabled only when the method contains at least one Major element.

To define Sample Preparation settings:

1. In the 'Add Analytical Assistant Components' dialog, click on Sample Preparation. A new dialog box opens. It contains the 'Sample type' drop down box. According to the selected sample type, the dialog offers more fields for further settings.

Note : The details specified in this dialog box will only influence the selection of instrumental parameters to reduce the sensitivity of the elements specified as Majors.

2. Define the sample preparation parameters as defined in the table below:

Sample Type

Select... if...

Solid (No dilution) the matrix to calibrate consists of

• solid samples,

• pressed powder samples that are prepared without a binder,

• undiluted liquid samples (e.g. oil).

Pressed the sample preparation method for pressed powders requires a binder. In such a case, the dilution ratio has to be specified.

Fused Bead the matrix consists of fused samples. In such a case, the dilution ratio has to be specified.

Liquid the matrix consists of diluted liquid samples. In such a case, the dilution ratio has to be specified.



Dilution

If you have selected a 'Dilution' or 'Pressed Powder' as sample type, you can indicate the dilution here:

Sample Weight [g] Specify the weight of the sample.

Diluent Weight [g] Specify the weight of the dilution material, e.g. flux, binder, etc.,

Ratio The ratio is calculated and indicated here.

Note : The values of Sample weight and Diluent weight are remembered in the Theoretical Alpha calculator.

Flux Conditions

If the sample is a fused bead, the flux conditions have to be configured here:

Flux Select the flux from the drop-down list.

Sample weight Specify the weight of the sample.

Li2B407 weight /

LiF weight /

LiBO2 weight

The fields are displayed according to the selected flux.

Specify the weight of the flux or of the flux components.

Ratio The ratio is calculated and indicated here.

Note : The values of Sample and Flux weight are recovered in the Theoretical Alpha calculator.

To apply sample preparation settings:

1. In the 'Sample preparation' dialog, click on OK to confirm the settings.

2. In the 'Add Components' dialog, click on Apply changes. The saturation flags algorithm is applied for selecting another line.

Scan/Energy Profiles

In order to investigate overlap problems it is recommended to perform scans and/or energy profiles. The 'Analytical Assistant Scan/Energy Profiles' dialog proposes default settings for the execution of scans and energy profiles and indicates the elements over which a scan should be run or for which an energy profile should be performed.

Note : The indications given in this dialog are based on the Truth Table for Overlap Corrections.

You can keep the default settings or modify them. Then, you create a batch for running the selected scans and energy profiles.

To open the Scan/energy Profiles dialog:

• On the 'Periodic Table' tab, click on the Scan/Energy Profiles icon.



The dialog box contains the following items:

Specific Conditions Scan / Energy Profile group box

Define the specific conditions (kV, mA, Elliptical Mask, Sample Rotation) that will be applied to all lines when executing the scans and energy profiles.

Batch box

Batch name

Enter the batch name here. By default, the method name is taken as batch name.

Scans group box

Speed Select Default in order to use the parameter proposed by the Analytical Assistant or enter a value for the scan speed in s/Interval.

Interval +/- from Peak This is the scan range around the peak.

Select Default or enter a value in degrees.

Energy Profiles group box

Interval Select Default in order to use the parameter proposed by the Analytical Assistant, 2nd order or 3rd order

Automatic Gain Control Select On or Off.

The grid The grid contains a list of all elements that are subject to a scan or an energy profile. The check boxes are activated according to the result indicated on the Overlaps tab. However, you can check any other box if you want to perform a scan or energy profile on another line.

The grid contains the following items:

Item Description

Scan Check this box if you want to perform a scan on the corresponding element line.

Energy Profile Check this box if you want to perform an energy profile on the corresponding element line.

Element Name of the element

Channel

Channel name Name of the line.

Component type Indicates whether the line is a Goniometer.

Sample Name Enter the name of the sample used for the scan or energy profile.



Sample Number Enter the sample number of the sample used for the scan or energy profile

Cassette Select the sample position from the drop down list.

Print Check this box if you want the result graph to be printed.

File The suggested scan results file name. By default, the file name is composed as follows: Batch name_Name of the element line_Component type.xml. Keep this name or enter a new file name.

Display online scans Check this box in order to display the scans on the screen while they are performed.

Buttons

Button Description

Create Batch From Method... Click on this button in order to create a batch containing the selected scans and/or energy profiles.

Info Click on this button in order to display information about the selected element(s) in terms of analytical parameters (lines, crystals, detectors, PBF, etc) that are best suited for your instrument configuration.

Overlaps Click on this button in order to display a table of analytes and overlapping elements in the selected method and recommendations for how to solve the overlap problems.

To create a batch for running scans / performing energy profiles:

1. Fill in the group boxes on top of the dialog.

2. Check the corresponding 'Scan' or 'Energy Profile' boxes in the grid or keep the recommended selection.

3. Enter Sample Name and Numbers.

4. Select the Cassette position from the drop down list.

5. Click on Create Batch From Method.... The batch is created.

Note : You should remember the batch name, as you might have to select it later in the batch editor.

The dialog is closed and you return to the Method editor.

Saving a Method

During creation or edition, you should save the method in regular intervals.

To save a Method:

In the Method pane, click on Save. The method is saved.


Running a Batch

Proceed as follows to run a batch:

1. Open the Batch manager .

2. From the 'Batches' combo box, select the batch that you want to run.

Note : Batches that have been created from another dialog, as for example the Methods editor, SCT Manager or the MVR Editor - Measure Calibration Standards, are labelled automatically as follows:

Batch Name Description

$METHODNAME$CS Measurement of control samples linked to a method

$METHODNAME$TS Measurement of type standard samples linked to a method

$METHODNAME$SS Measurement of setting-up samples linked to a method

$METHODNAME$CA Measurement of calibration standard samples linked to a method

3. If the sample list and sequence is satisfactory, press the 'Start' button. A progression bar indicates the status of the batch execution. The samples will be analysed in sequence without any further operator involvement.

If you want to change the order of samples to be analyzed, exclude samples or cancel the analysis, use the appropriate Batch Tools.

The colors in the first column of the grid have the following meaning:

Color Description

blue The analysis is currently executed.

green The analysis is completed and OK

red The analysis is executed, but not OK.

Note : A batch may contain one or more sample lists. If different types of sample lists are contained, then the sample identity headings are always adapted to the current list. You can move samples between sample lists and the headings will adjust accordingly.

Once all tasks of the flow chart are performed, go to the next step.




Define the second Method Creating a Method II: Additional Parameters

Figure 7.5

In the same way, go through all the Methods till the end of the list.

Following the Help Online guide allows the user to perform a complete Calibration.

At this point the instrument is ready to perform Quantitative Analysis.

Note : The Quantitative Analysis is described in section N° 9.

8

INSTRUMENT CALIBRATION

INSTRUMENT CALIBRATION Chapter 8


8 INSTRUMENT CALIBRATION

Introduction

An analytical program has to be created when the instrument has not yet been calibrated, or when an extension to the existing calibrations is needed to support other analytical applications. The X-ray analyser is a comparative measuring system. To display the concentrations of unknown samples, the system must have been calibrated previously. To do so, a set of certified standard samples is necessary. These samples are measured and the intensities of each element is stored in a calibration result file. The relationship between the concentrations and the instrumental response for each element and sample is then calculated by the computer system and stored, as a polynomial, in the corresponding analytical program. The instrument is now ready to measure unknown samples, matching with the matrix of the calibration standards. In X-ray fluorescence analysis some physical and instrumental errors will appear:

♦ Physical errors are matrix effects due to absorption and enhancement. To correct these errors the mathematical models can be used through the computer system.

♦ Instrumental errors are mainly line overlaps due to insufficient resolution, and instrumental response drift through the time. Line overlaps can be corrected mathematically whereas to correct the instrumental drift, the system response has to be re-adjusted periodically by measuring appropriate reference samples, known as Setting-up Samples.

Instrument calibration with OXSAS

Refer to section N°7 Analytical Assistant with OXSAS of this manual.

9

PERIODIC MAINTENANCE

PERIODIC MAINTENANCE Chapter 9


9 PERIODIC MAINTENANCE The frequency of the maintenance task can vary depending of the cleanliness (dust) of the environment (lab).

As an example the table below provides information on the maintenance and the service required by the instrument analyzing 300 solid samples per day.

Location Work to be done Weekly Monthly Yearly Software Database backup Perform Cabinet All fans Check Dust filters Check Change Inside the cabinet Clean Sample Sample cassette Clean load/unload Sample Magazine Clean XY Magazine Clean Vacuum circuit Oil pump level Check/Fill Change Water circuit Deionized water level Check P10 Gas circuit P10 Gas bottle High pressure level Check P10 Gas bottle Low pressure level Check Monochromators All energy profiles Check Adjust All thresholds and windows Check All detectors resolutions Check XRD Energy profile Check Adjust Threshold and window Check Detector resolution Check Gonio Energy profiles Check Adjust Thresholds and windows Check Detectors FPC and SC resolutions Check Stability Long and short term test Check

For some items listed in the above table, the frequency of the maintenance tasks can vary depending of the number and the nature of the samples analysed.

Software data security

If the hard disc becomes damaged and not accessible, it is possible that the Goniometer Calibration (High Voltage and Position Calibration) and User data (Methods, Setting-up Standards, and Analytical Results etc.) could be lost. Therefore, we strongly advise that the user makes Backup copies of these files at regular intervals.

Data saving is essential!

Very important: Before undertaking any Backup or Restore operation, OXSAS must be IN OFFLINE MODE.

Follow the next steps or refer to the OXSAS Online Help in Backup/Restore.

OXSAS provides two items from the File menu for backing up or restoring the database.

Chapter 9 PERIODIC MAINTENANCE

To backup the database

1. Activate the Offline mode.

Figure 9.1

Figure 9.2

2. From the main menu, select File - Backup Database. The DB Backup dialogue opens.

3. Enter the file name or keep the default one.

4. By default, the backup is stored in the Thermo\OXSAS_Data\Backup folder. If you want to browse for an other destination, click on ....

Files & Folders to Backup

By default, all files in following folders and sub-folders should be backed up:

• [Data Path]\Thermo\OXSAS_Data

• [Data Path]\UQ5\User



• [Data Path]\UQ\Data

Figure 9.3

5. If you want to back up Analyses and/ or the Language DB too, check the corresponding box.

6. Click on Backup in order to start the backup. A progression bar indicates that the backup is being performed. When the backup is completed, the progression bar dialogue is closed.

Figure 9.4

7. Copy the OXSAS_Data folder to a network disk or to a removable disk (CD-ROM or similar).



8. The next figures show the path to find the folders and files to copy.

Figure 9.5 Figure 9.6

Figure 9.7 Figure 9.8

In the above example, the highlighted files have been named using the date of backup.



To restore a database

1. Activate the Offline mode.

Figure 9.9

Figure 9.10

2. From the main menu, select File - Restore Database. The DB Restore dialogue opens.



Figure 9.11

3. In the File name list box, select the file that you want to restore or browse for an other destination, click on ....

Figure 9.12

4. If you want Analyses and/or the Language DB to be restored, too, check the corresponding box.

5. Click on Restore in order to start restoring the selected database.

For the path refer to the figures 9.5 to 9.8.



Instrument hardware

When performing any maintenance task, the instrument must be in idle state.

Sample cassettes

♦ Clean the sample cassettes or sample supports outside and inside with a soft paper and isopropyl alcohol.

12 Position Sample Magazine

♦ Using a vacuum cleaner, remove the dust and the residues, inside and outside the numbered rings.

X-Y magazine trays

♦ Remove the trays from the magazine clean the trays with soft paper and isopropyl alcohol.

♦ While the trays are removed clean the table of the X-Y magazine with a vacuum cleaner, soft paper and isopropyl alcohol.

♦ Put the trays back to there respective locations.

Vane stage pump oil level

Prior to check the oil level, the right side panel of the instrument has to be removed.

1 Remove the 2 Allen screws with a 5mm Allen key.

2 Slide the panel out of its position.

3 Remove the ground strap from the panel and put in it a safe place.

2

1

Figure 9.13



Once the panel is removed, the vacuum system and X-ray cooling circuit are accessible.

Vacuum Pump

X-ray coolingCircuit

Figure 9.14

♦ Check the vacuum pump oil level at least once a week.

♦ To check the oil level the pump must be stopped shortly.

♦ The oil level must be checked as the pump is hot.

♦ To stop the pump, follow the next instructions:

With OXSAS software:

1 In OXSAS main menu select Tools

2 Select Monitoring and Troubleshooting

3 Select Monitoring Peripheral Devices and select ICS

4 In the following Messages to Send/Receive window, type V1 0 (V1 space zero) and click the button Send

Figure 9.15



1. In the following Messages to Send/Receive window type: P2 0 (P2 space zero) and click the button Send.

Figure 9.16

♦ Check the pump is stopped.

♦ The oil level does stabilise.

♦ It is know time to check the oil level.

Maximumlevel

Intermediarylevel

Minimumlevel

OKOK

Figure 9.17

Check the oil level: If OK,

restart the pump by typing: in the Messages to Send/Receive window, type: P2 1 and Send in the Messages to Send/Receive window type: V1 1 and Send Put all back in reverse order.

If not OK,

top up with new oil CMP ELITE Z.

Use only oil prescribed by Thermo Electron.



To top up:

1 Remove the white plastic shield. 2 Remove the 2 black stoppers

1

2

Figure 9.18

3 Top up the oil to the appropriate level

3

Figure 9.19

4 Put the 2 black stoppers back 5 Put the white shield back 6 Restart the pump: In the Messages to Send/Receive window type P2 1 Send 7 Check the pump is running 8 Restart the pump: In the Messages to Send/Receive window type V1 1 Send 9 Reconnect right panel ground strap 10 Reinstall right panel and tighten the 2 screws



Deionized water level

If the alarm N° 8719 Warning Secondary Water Level Too Low arises it is time to check the deionized water level in the reservoir.

Prior to top up the deionized water reservoir, the right side panel of the instrument has to be removed.

1 Remove the 2 Allen screws with a 5mm Allen key. 2 Slide the panel out of its position. 3 Remove the ground strap from the panel and put in a safe place.

To top up the deionized water reservoir:

1 Remove white plastic tap 1. 2 Top up the green plastic tank with deionized water using a squeeze bottle 2.

1

2

Figure 9.20

3 Put the white plastic stopper 1 back. 4 Reinstall the right panel ground strap. 5 Reinstall right panel and tighten the 2 screws.



Dust filter

The frequency of changing the dust filter does depend of the cleanness of the laboratory.

Bad venting of the X-ray generator, due to dirty dust filter may lead to an X-ray generator shut down.

To change the dust filter:

1 Remove left side panel

2

1

Figure 9.21

2 Slide the panel out of its position. 3 Remove the ground strap from the panel and put it in a safe place.

Once the left panel is removed the dust filter is accessible.



3 Remove the dust filter by pulling it gently horizontally out.

ARL GenX

Filter

Figure 9.22

4 Take new dust filter; install it by pushing it gently horizontally in. 5 Reconnect the ground strap. 6 Reinstall the left panel and tighten the 2 screws



Ar-CH4 P10 gas

Check the content of the gas cylinder weekly. If the indicator 4 shows a pressure < 2 bars, the gas cylinder has to be exchanged.

1 Close tap 2 by turning it clockwise. 2 Turn fitting 3 clockwise (reversed thread for P10 gas) and remove the complete pressure

regulator from the cylinder 1.

ArC

H4

1

2

3

4

5

6

0.25

Figure 9.23

3 Supply new full cylinder 1 and reinstall complete pressure regulator, turn fitting 3 counter clockwise and lock it.

4 Open cylinder tap 2 counter clockwise. 5 Check the working pressure on indicator 5. It must indicate 0.25 bars. Adjust if necessary

by tuning red pressure setting knob 6. 6 Wait the system does reach the final gas regulation step. To monitor the gas pressure

regulation and flow use Status Monitoring facility as described in section Instrument Preparation.

Note: The regulation delay may last some minutes.




ANALYTICAL PARAMETERS

Monochromators

Energy profiles and detectors resolutions

Each monochromator is set up to selectively detect only those photons with a wavelength that is specific for an individual element. All the detectors used for the various monochromators produce a signal size proportional in output to the X-ray energy being measured.

X-ray wavelength and energy are inversely related, whereas for a given crystal/detector combination the longer the wavelength the higher the angle. The following equations show the relationships between the angle, the wavelength and the energy:

E = 12.4 / λ

n λ = 2 d Sin θ

In the signal measuring systems, a constant size of pulse is required by the discrimination and counting (scalar) system. To maintain this for each monochromator it is essential that the high voltage applied to the detector is in accordance with the element line angle of the monochromator (See equations above).

For each monochromator this high voltage has to be determined by the High Voltage Calibration to maintain the amplitude of the pulses at a channel value of 75 in the measuring system.

Resolution of the detector is expressed as Resolution = (W / V) x 100 where W is the peak width (of the energy profile) at half-width and V is the maximum of the pulse amplitude distribution.

For gas detectors, stability of the detectors depends on the cleanliness of the anode wire. If the gas-fillings are not pure enough or small particles get deposited on the anode wire, they may distort the local electric field (by changing the effective diameter of the anode wire). This may change the gas gain factor causing unstable detection. Checking the detectors pulse amplitudes and resolutions, are part of the operator maintenance. It does contribute to the follow up of the instrumental performance.

The goal is to perform an energy profile with the same working parameters as used originally and to compare the original data with the actual data.

Running an Energy Profile:

From the main menu select Tools


Figure 9.24

Select Check Detector

Figure 9.25

Select Run Energy Profile

Figure 9.26

In the next window select the appropriate Parameters Name.

Remark: As a rule the Parameters Name to check the resolution and the High Voltage settings, is: X_Mono_Element symbol and line_L.xml or

♦ Parameters Name: For Monochromator Cr ka1,2 select X_Mono_Cr_L

♦ Sample Position: Specify the cassette or sample position number.



♦ Channel Type: Specify Monochromators

♦ Available Monochromators: Cr ka

♦ Tube Current: 0 mA (the system will automatically set the X-Ray Tube emission current to reach 10 kilo counts /sec).

Remark: As a rule the Energy Profiles performed to check the resolution and the High Voltage Settings are executed with AGC OFF and with 10 kilo counts / sec. The X-Ray Emission Current (mA) is adjusted accordingly.

♦ When all the inputs are OK Click Start Profile

Figure 9.27

The system will execute the Energy Profile

♦ Select Investigate Energy Profile

♦ Select File

♦ Select Result file name

♦ Click Open in new window



Figure 9.28

♦ Click Resolution

Figure 9.29

Compare last graphic parameters with the original one.

The detector resolution and the peak amplitude should match.




WDS Goniometer

Investigate energy profile and detector resolution

When the goniometer changes from element to element by moving its crystal/detector combinations, different X-ray wavelengths are received by the detectors. All the detectors used in the goniometer produce a signal size proportional in output to the X-ray energy being measured.

X-ray wavelength and energy are inversely related, whereas for a given crystal/detector combination the longer the wavelength the higher the angle. The following equations show the relationships between the angle, the wavelength and the energy:

E = 12.4 / λ

n λ = 2 d Sin θ

In the signal measuring systems, a constant size of pulse is required by the discrimination and counting (scalar) system. To maintain this over the whole wavelength range means that the voltage applied to the detectors must be programmed with angle (see equations above).

For each detector/crystal combination, a non-linear calibration is maintained to enable this to be done. As the angle increases, the voltage is increased by a 2nd order polynomial held in the microprocessor relating angle and voltage, needed to maintain 75 steps pulses in the measuring system.

All parameters are directly handled as steps. The relationship between the Two Theta angle and the high voltage applied to the detector is expressed with the following formula:

HVPS = exp(A0 + A1 * ln(sin(θ)) + A2 * ln(sin (θ))2)

Note : The detector high voltage for element lines is only calculated automatically if a 0 (zero) value is specified for the corresponding line in the line library. Conversely, the high voltage will be adjusted according to the specified value.

In case the high voltage calculated by above equations does not result in an energy profile peak maximum situated around 75 steps for a specific element line, the 0 value may temporarily be changed in a given line to a value which causes the peak to be located at the correct position.

The same series of synthetic samples (ARL-200 series) as for position calibration is used to perform the determination of the high voltage calibration coefficients. The parameters used are factory set up and make the whole process automatic. Checking the detectors pulse amplitudes and resolutions, are part of the operator maintenance. It does contribute to the follow up of the instrumental performance.

The goal is to perform an energy profile with the same working parameters as used originally and to compare the original data with the actual data.


Running an Energy Profile:

♦ From the main menu select Tools

Figure 9.30

♦ Select Check Detector

Figure 9.31

♦ Select Run Energy Profile

Figure 9.32

♦ In the next window select the appropriate Parameters Name. The WDS Goniometer does support two detectors; a Flow Proportional Counter (FPC) and a Scintillation Counter (SC).

For FPC two element lines are dedicated to check the detectors resolution; Fekα1,2 and Sikα1,2.



For SC one element line is dedicated to check the detector resolution; Mokα1,2.

The energy profiles have to be performed on these lines.

Remark: As a rule the Energy Profiles performed to check the resolution and the High Voltage Settings are executed with AGC OFF and with 10 kilo counts / sec. The X-Ray Emission Current (mA) is adjusted accordingly.

♦ Parameters Name: For Goniometer X_LiF200_FPC_0.15_Fe_L (for Fe line)


♦ Channel Type: Specify Goniometer 1 (ARL F45) or ARL SmartGonio

♦ Tube Current: set mA to reach 10 kilo counts /sec.


Figure 9.33



♦ Select File





Figure 9.34


Figure 9.35





Compact XRD Goniometer


Note: The principle is the same as for the WDS Goniometer to the difference of the Parameters Name Selection

Remark: As a rule the Energy Profiles performed to check the resolution and the High Voltage Settings are executed with AGC OFF and with 10 kilos counts / sec. The X-Ray Emission Current (mA) is adjusted accordingly.

♦ Parameters Name: For XRD XRD_DETECTOR ………(for XRD NiO Line)


♦ Channel Type: Specify XRD System



Figure 9.36



♦ Select File





Figure 9.37


Figure 9.38





Full XRD Goniometer for Workstation


Note: The principle is the same as for the WDS Goniometer to the difference of the Parameters Name Selection

Remark: As a rule the Energy Profiles performed to check the resolution and the High Voltage Settings are executed with AGC OFF and with 10 kilos counts / sec. The X-Ray Emission Current (mA) is adjusted accordingly.

♦ Parameters Name: For Full XRD X_XRD Tube_Quartz_112


♦ Channel Type: Specify Goniometer XRD 1



Figure 9.39





♦ Select File



Figure 9.40


Figure 9.41






Investigate Goniometer scans

Principle of Goniometer Positioning

In the optical encoder a radial fixed grating is employed which interferes with the mobile grating of the detector or crystal carrier. These interferences are based on the Moiré fringe principle.

The goniometers used in the ARL X-Ray spectrometers have separate motors to drive the crystal and detector assemblies. These motors are controlled by the corresponding microprocessor, which receives feedback of position from the optical encoder reader heads fitted to the detector and crystal drives.

The 2:1 relationships between angles of the detector and crystal and their respective encoders are maintained as two separate linear equations in the corresponding microprocessor. The coefficients for these equations are determined with the position calibrations.

Important : No mechanical adjustments are necessary to calibrate the goniometer for position.

The ARL X-ray spectrometers can be equipped with different types of goniometer:

• F45 goniometer

• SmartGonioTM These goniometers have a separate fixed grating for each drive (i.e. crystal and detector). This grating has 2500 lines per 360°, e.g. 6.94444 measured fringes per 1° degree of angular rotation. Each fringe is further subdivided electronically into 65536 parts giving an angular resolution better than 0.000045°.

About Position Calibration

For the goniometer to be able to work, calibrations must be determined for each crystal/detector/collimator combination. These consist of determining, for a given crystal/detector/collimator combination, the relationship between the θ Bragg angle and the crystal position, and the relationship between the 2 θ Bragg angle and the detector position.

The execution of the position calibrations is only necessary:

• when the instrument is installed,

• if the window of the FPC detector is changed,

• if any other mechanical interventions have to be made on the goniometer. A series of synthetic samples (ARL-200 series) are supplied with each instrument to perform the determination of the position calibration coefficients. The parameters used are factory set up and make the whole process automatic.

To check if the goniometer does properly position on the desired angle, scans have to be performed on the reference elements used to perform the Position Calibration. See table hereafter.



Tables of Crystals, Detectors and Collimators combinations

Goniometer F45 Position Calibration Specifications

Crystal Detector Collimator Scan name Element Sample Theoretical 2 θ Tolerance

LiF 200 FPC 0.15° X_POS_LiF200_FPC_0.15_Cu_Ka1,2 X_POS_LiF200_FPC_0.15_Ba_Ka1,2 X_POS_LiF200_FPC_0.15_Sn_Ka1,2

CuKα 1,2 BaLα 1 SnLα 1

200 D 45.03° 87.16° 126.765°

+/- 0.01° (5)

LiF 200 FPC 0.25° X_POS_LiF200_FPC_0.25_Cu_Ka1,2 X_POS_LiF200_FPC_0.25_Ba_Ka1,2 X_POS_LiF200_FPC_0.25_Sn_Ka1,2

CuKα 1,2 BaLα 1 SnLα 1

200 D 45.03° 87.16° 126.77°

+/- 0.01° (5)

LiF 200 SC 0.15° X_POS_LiF200_SC_0.15_Ba_Ka1,2 X_POS_LiF200_SC_0.15_Cu_Ka1,2 X_POS_LiF200_SC_0.15_Ba_La1

BaKα 1,2 CuKα 1,2 BaLα 1

200 D 11.02° 45.03° 87.16°

+/- 0.01° (5)

LiF 200 SC 0.25° X_POS_LiF200_SC_0.25_Ba_Ka1,2 X_POS_LiF200_SC_0.25_Cu_Ka1,2 X_POS_LiF200_SC_0.25_Ba_La1


200 D 11.02° 45.03° 87.16°

+/- 0.01° (5)

PET FPC 0.15° X_POS_PET_FPC_0.15_Ca_Ka1,2 X_POS_PET_FPC_0.15_Si_Ka1,2 X_POS_PET_FPC_0.15_Al_Ka1,2

CaKα 1,2 SiKα 1,2 AlKα 1,2

200 B 45.12° 108.95° 144.54°

+/- 0.02° (5) R1



200 B 45.12° 108.95° 144.54°

+/- 0.02° (5) R1



200 B 45.12° 108.95° 144.54°

+/- 0.02° (5) R1

AX03 FPC 0.15° X_POS_AX03_FPC_0.15_Mg_Ka1,2 X_POS_AX03_FPC_0.15_Na_Ka1,2 X_POS_AX03_FPC_0.15_F_Ka1,2

MgKα 1,2 NaKα 1,2 FKα 1,2

200 A ≈20° ≈24.5° ≈38.20°

+/- 0.04° R2

AX03 FPC 0.25° X_POS_AX03_FPC_0.25_Mg_Ka1,2 X_POS_AX03_FPC_025_Na_Ka1,2 X_POS_AX03_FPC_0.25_F_Ka1,2


200 A ≈20° ≈24.5° ≈38.20°

+/- 0.04° R2

AX06 FPC 0.60° X_POS_AX06_FPC_0.6_Mg_Ka1,2 X_POS_AX06_FPC_0.6_Na_Ka1,2 X_POS_AX06_FPC_0.6_F_Ka1,2


200 A ≈20° ≈24.5° ≈38.20°

+/- 0.04° R2

LiF 220 FPC 0.15° X_POS_LiF220_FPC_0.15_Cu_Ka1,2 X_POS_LiF220_FPC_0.15_Cr_Ka1,2 X_POS_LiF220_FPC_0.15_Ti_Kb1,2

CuKα 1 CrKα 1,2 TiKβ 1,3

200 C 65.49° 107.02° 123.94°

+/- 0.01° (5)

LiF 220 FPC 0.25° X_POS_LiF220_FPC_0.25_Cu_Ka1,2 X_POS_LiF220_FPC_0.25_Cr_Ka1,2 X_POS_LiF220_FPC_0.25_Ti_Kb1,2

CuKα 1 CrKα 1,2 TiKβ 1,3

200 C 65.49° 107.02° 123.94°

+/- 0.01° (5)

LiF 220 SC 0.15° X_POS_LiF220_SC_0.15_Ba_Ka1 X_POS_LiF220_SC_0.15_Mo_Ka1 X_POS_LiF220_SC_0.15_Fe_Ka1

BaKα 1 MoKα 1 FeKα 1

200 D 15.54° 28.84° 85.65°

+/- 0.01° (5)

LiF 220 SC 0.25° X_POS_LiF220_SC_0.25_Ba_Ka1 X_POS_LiF220_SC_0.25_Mo_Ka1 X_POS_LiF220_SC_0.25_Fe_Ka1

BaKα 1,2 MoKα 1,2 FeKα 1,2

200 D 15.60° 28.90° 85.73°

+/- 0.01° (5)

Ge 111 FPC 0.15° X_POS_Ge111_FPC_0.15_Ca_Ka1,2 X_POS_Ge111_FPC_0.15_Cl_Ka1,2 X_POS_Ge111_FPC_0.15_S_Ka1,2

Cakα 1,2 ClKα 1,2 SKα 1,2

200 B 61.90° 92.76° 110.69°

+/- .02°

Ge 111 FPC 0.25° X_POS_Ge111_FPC_0.25_Ca_Ka1,2 X_POS_Ge111_FPC_0.25_Cl_Ka1,2 X_POS_Ge111_FPC_0.25_S_Ka1,2

CaKα 1,2 ClKα 1,2 SKα 1,2

200 B 61.90° 92.76° 110.69°

+/- .02°

AX11 FPC 2.60° X_POS_AX11_FPC_2.60_C_Ka1,2 R3 X_POS_AX11_FPC_2.60_B_Ka1,2 R3

CKα 1,2 BKα 1,2

200 G ≈47.95° ≈75.84°

+/- 0.04° R2

AX16 FPC 2.60° X_POS_AX16_FPC_2.60_C_Ka1,2 R3 X_POS_AX16_FPC_2.60_B_Ka1,2 R3

CKα 1,2 BKα 1,2 200 G ≈32.42°

≈49.95° +/- 0.04° R2

TLAP FPC 0.15° X_POS_TLAP_FPC_0.15_Mg_Ka1,2 X_POS_TLAP_FPC_0.15_Na_Ka1,2 X_POS_TLAP_FPC_0.15_F_Ka1,2

MgKα 1,2 NaKα1,2 FKα 1,2

200 A 45.08° 54.98° 90.48°

+/- .03°



200 A 45.08° 54.98° 90.48°

+/- .03°



Crystal Detector Collimator Control Scan Name Element Sample Theoretical 2 θ Tolerance



200 A 45.08° 54.98° 90.48°

+/- .03°

AX09 FPC 2.60° X_POS_AX06_FPC_0.6_N_Ka1,2 R3 NKα 1,2 200 BN ≈41.11° +/- 0.04° R2

LiF 420 SC 0.15° X_POS_LiF420_SC_0.15_Ba_Ka1 X_POS_LiF420_SC_0.15_Sr_Ka1 X_POS_LiF420_SC_0.15_Pb_La1

BaKα 1 SrKα 1 PbLα 1

200 D 24.71° 58.19° 81.50°

+/- 0.02

InSb FPC 0.60 ° X_POS_InSb_FPC_0.6_S_Ka1,2 R3 X_POS_InSb_FPC_0.6_P_Ka1,2 R3 X_POS_InSb_FPC_0.6_Si_Ka1,2 R3

Skα 1,2 Pkα 1,2 SiKα 1,2

200 B 91.82° 110.81° 144.59°

+/- 0.02

AX20 FPC 2.60° X_POS_AX06_FPC_2.6_N_Ka1,2 R3 X_POS_AX06_FPC_2.6_N_Ka1,2 R3

CKα 1,2 BKα 1,2 200 G ≈26.65°

≈40.80° +/- 0.04° R2

ADP FPC 0.25° X_POS_ADP_FPC_0.25_Cl_Ka1,2 R3 X_POS_ADP_FPC_0.25_Si_Ka1,2 R3 X_POS_ADP_FPC_0.25_Mg_Ka1,2 R3

ClKα 1,2 SiKα 1,2 MgKα 1,2

200 A 52.76° 84.08° 136.66°

+/- 0.04°

ADP FPC 0.60° X_POS_ADP_FPC_0.6_Cl_Ka1,2 R3 X_POS_ADP_FPC_0.6_Si_Ka1,2 R3 X_POS_ADP_FPC_0.6_Mg_Ka1,2 R3

ClKα 1,2 SiKα 1,2 MgKα 1,2

200 A 52.76° 84.08° 136.66°

+/- 0.04°

Remarks: R1 The 2θ are relative to the 2d of the crystal, which depends upon its temperature (see “Regulated

temperatures ARL XRF Instruments”). R2 The 2d of the synthetic multilayered crystalline structure can slightly vary from one crystal to another. See certificate.

Therefore the 2θ angles of the elements used for the PCAL and the control scan, have to be recalculated and actualised in the software tables.

R3 The crystal positions 6, 8 or 9 may be used for different type of crystals. The fact is that the AX09, AX11, AX16, AX20, InSb and ADP Crystals don’t have a specific predefined position number.

Position Calibration Coefficients: Offset Slope Delta Det 1 ≈ 0 ≈ 6.94 ≈ 0 Det 3 ≈ 0 ≈ 6.94 ≈ 246



Smart GonioTM Position Calibration Specifications

Crystal Detector

Collimator

Coefficients Offset Slope Delta Scan name Element Sample

Theoretical 2 θ

Tolerance

LiF 200 FPC R3 -312 / 6.944 / -625 X_POS_LiF200_FPC_0.29_Cu_Ka1,2 X_POS_LiF200_FPC_0.29_Ti_Ka1,2 X_POS_LiF200_FPC_0.29_Ca_Ka1,2

CuKα 1,2 TiKα 1,2 CaKα 1,2

200 C 45.03° 86.14° 113.09°

+/- 0.01° (5)

LiF 200 SC R3 -312 / 6.944 / 41.7 X_POS_LiF200_SC_0.29_Ba_Ka1,2 X_POS_LiF200_SC_0.29_Cu_Ka1,2 X_POS_LiF200_SC_0.29_Ba_La1


200 D 11.02° 45.03° 87.16°

+/- 0.01° (5)

PET FPC R3 -1562 / 6.944 / -625 X_POS_PET_FPC_0.29_Ca_Ka1,2 X_POS_PET_FPC_0.29_Si_Ka1,2 X_POS_PET_FPC_0.29_Al_Ka1,2


200 B 45.12° 108.95°144.54°

+/- 0.04° (5) R1

AX06 FPC R3 R4 ./ 6.944./.-625 X_POS_AX06_FPC_0.29_Mg_Ka1,2 X_POS_AX06_FPC_0.29_Na_Ka1,2 X_POS_AX06_FPC_0.29_F_Ka1,2


200 A ≈20° ≈24.5° ≈38.20°

+/- 0.04° R2

LiF 220 FPC R3 R4 ./ 6.944./.-625 X_POS_LiF220_FPC_0.29_Cu_Ka1,2 X_POS_LiF220_FPC_0.29_Fe_Ka1,2 X_POS_LiF220_FPC_0.29_Cr_Kb1,2

CuKα 1 FeKα 1 CrKα 1

200 C 65.49° 85.65° 107.02°

+/- 0.01° (5)

LiF 220 SC R3 R4 ./ 6.944./. 41.7 X_POS_LiF220_SC_0.29_Ba_Ka1 X_POS_LiF220_SC_0.29_Sr_Ka1 X_POS_LiF220_SC_0.29_Fe_Ka1

BaKα 1 SrKα 1 FeKα 1

200 D 15.54° 35.80° 85.65°

+/- 0.01° (5)

Ge 111 FPC R3 R4 ./ 6.944./.-625 X_POS_Ge111_FPC_0.29_Cu_Ka1,2 X_POS_Ge111_FPC_0.29_Ca_Ka1,2 X_POS_Ge111_FPC_0.29_S_Ka1,2

Cukα 1,2 CaKα 1,2 SKα 1,2

200 B 27.31° 61.90° 110.69°

+/- .02°

Remarks: R1 The 2θ are relative to the 2d of the crystal, which depends upon its temperature (see “Regulated

temperatures ARL XRF Instruments”). R2 The 2d of the synthetic multilayered crystalline structure can slightly vary from one crystal to

another. See certificate. Therefore the 2θ angles of the elements used for the PCAL and the control scan, have to be recalculated and actualised in the software tables.

R3 The collimator is a fixed device. It is factory build in. Nevertheless the name of the scan is related to the type of collimator. 3 different types of collimators are available:

Collimator Scan name 0.6° X_POS_Crystal_Detector_0.6_El_Line 0.29° X_POS_Crystal_Detector_0.29_El_Line 0.17° X_POS_Crystal_Detector_0.17_El_Line

R4 The crystal positions 1 or 2 may be used for different type of crystals. The fact is that the PET, AX06, LiF 220, and Ge111 Crystals, don’t have a specific predefined position number.

If the crystal position is 1, the offset is = - 312 (Negative 312) If the crystal position is 2, the offset is = - 1562 (Negative 1562)


Compact XRD Position Calibration Specifications

Figure 9.42

Table of compounds used for position calibration

Detector Primary Beam Collimator

Sample Compound 2 Theta Theoretical Offset Slope Delta

Kr -5° XRDU ZnOC 114.33 0 6.944 30 Kr -5° XRDU NiO 130.16 Kr 20° XRDU CaCO3 92.21 0 6.944 200 Kr 20° XRDU ZnOC 114.33



Full XRD for Workstation Position Calibration Specifications

Figure 9.43

Position Calibration and Theta Resolution test

Figure 9.44



To perform a scan with WDS goniometer

♦ In the main menu select: Analysis and Data, Qualitative Scans

Figure 9.45

♦ In the Scan Name list box select the appropriate scan

Figure 9.46

♦ Check the parameters do match and click Start Scan.

Remark : As a rule the name of the scan parameter is:X_POS_Crystal name_Detector name_Collimator type_El Symbol_El Line.xml

See example below



Figure 9.47

♦ Once the scan is executed click Investigate Scans ♦ Click on File, select Open in New Window, and select the dedicated result file name.

Figure 9.48

♦ Check the real 2 θ angular position does match the theoretical one. If yes, the Goniometer Position Calibration is OK.



To perform a scan with Compact XRD goniometer


Figure 9.49


Figure 9.50


Remark : As a rule the name of the scan parameter is: XRD _Primary Beam Collimator type .xml

See example above.



Once the scan is executed click Investigate Diffractograms

Figure 9.51

♦ Click on File, select Open in New Window, and select the dedicated result file name.

♦ Identify the compounds

Figure 9.52

♦ Check the real 2 θ angular position does match the theoretical one. If yes, the XRD Goniometer Position Calibration is OK.



To perform a scan with Full XRD goniometer


Figure 9.53


Figure 9.54


Remark: As a rule the name of the scan parameter is: X_XRD_XRD Tube.xml

See example above.



♦ Once the scan is executed click Investigate Diffractograms

Figure 9.55

♦ Click on File, select Open in New Window, and select the dedicated result file name.

♦ Identify the compounds

Figure 9.56

♦ Check the real 2 θ angular position does match the theoretical one. If yes, the Full XRD Goniometer Position Calibration is OK.




ARL 9900 Series instrument global maintenance

As an example the table below provides information on the maintenance and the service required by the instrument analyzing 300 solid samples per day.

The yearly maintenance and service tasks listed in the greyed boxes can only be performed by certified and authorized Thermo service engineers, unless the user is properly trained by the TTI.

Location Work to be done Weekly Monthly Yearly Every 2 years

Every 3 years

Software Database backup Perform Cabinet All fans Check Change All dust filters Check Change Inside the cabinet Clean Sample Sample cassette Clean load/unload Sample Magazine Clean XY Magazine Clean Shutter assembly Clean Revise Load lift Revise Transfer Revise Analyse lift Revise Sample rotation Check Vacuum circuit Oil pump level Check/Fill Change Oil vacuum pump Revise Oil vacuum pump filter Change Molecular pump Add grease Change Spectro vacuum valve Change Prim. Ch. vacuum and venting valves Change Both vacuum level Check Adjust Water circuit Deionized water level Check Deionized water flow Check Deionized water temperature Check Deionized filter cartridge Change Deionized water resistivity Check Prim. Water flow Check Prim. Water temperature Check Water valves Change All tap water tubes Clean Water leakage ( Collar tightness ) Check X-Ray tube P.S. X-Ray tube HV connection Check X-Ray tube P.S. HV connection Check HV silicone washers Change Test of the interlock circuit Check P10 Gas circuit P10 Gas bottle High pressure level Check P10 Gas bottle Low pressure level Check P10 Gas Interlock Check P10 Gas regulation valves Change P10 Gas overpressure valve Change Prim. Beam Dev. Prim. Beam Device assembly Check Monos All energy profiles Check Adjust All thresholds and windows Check All detectors resolutions Check Mono filter positioning Check XRD Energy profile Check Adjust Threshold and window Check Detector resolution Check Scan check positions Check Adjust Gonio Energy profiles Check Adjust Thresholds and windows Check Detectors FPC and SC resolutions Check Scan check positions Check Adjust Stability Long and short term test Check



Notes : The frequency of the maintenance tasks can vary depending of the number and the nature of the samples analysed.

The frequency of the maintenance tasks can vary depending of the cleanliness (dust) of the environment (laboratory).

A

APPENDIX A

Appendix A Appendix A

A APPENDIX A

Introduction

X-ray spectrochemical analysis is based on the fact that the chemical elements emit characteristic radiations when subjected to appropriate excitation. The emission of characteristic line spectra can be induced by either the impact of accelerated particles such as electrons, photons, alpha particles and ions; or by the impact of high energy radiations from an X-ray tube or from a suitable radioactive source. Generally, direct electron excitation is used in electron microprobe techniques, while radioisotope sources and proton generators are commonly associated with energy dispersion.

X-ray Emission In a typical spectroscopic experiment, we usually interact with the neutral atom by supplying it with a certain amount of energy. The nature of the supplied energy can vary depending on the technique. For example, in a XRF experiment, we expose the atoms to X-radiation (called primary X-rays) while in an optical emission experiment we might use an electrical discharge or a high temperature plasma source to provide certain quantity of energy. The atom then absorbs some or all of this energy if this helps to displace the electrons. The displacement of electrons can occur within the atom, i.e. the electron goes to a higher energy state within the same atom by absorbing the incident energy, in which case we obtain an excited atom. The electron can also leave the atom in which case we get an ionised atom (a positive ion) since there will be excess positive charge in the nucleus. In a general situation, both excited atoms and ions may be present together.

In our case, when the primary X-rays from the X-ray tube interact with the sample, the following phenomena take place:

Photoelectric absorption

Scattered X-rays

Transmitted X-rays

X-ray FluorescenceAuger effect

Coherent

Incoherent

Figure A.1

AA83654 ARL 9900 INTELLIPOWER Series User Manual A-1


Photoelectric absorption

When a sufficiently energetic X-ray photon interacts with an atom, several phenomena take place. One interaction involves the transfer of the photon energy to one of the electrons of the atom (e.g. a K shell electron) resulting in its ejection from the atom. The distribution of electrons in the ionized atom is then out of equilibrium and within an extremely short time returns to the normal state, by transitions of electrons from outer shells to inner shells. Each such electron transfer, for example from the L shell to the K shell, represents a loss in the potential energy of the atom; this energy reappears as a photon (in this case a Kα photon) whose energy is the difference between the binding energies of the two shells. One of the two processes can take place, namely:

a) The X-ray photon escapes from the atom and contributes to a characteristic radiation of the atom (Figure A.2 left).

K

L

M

NO

hν

hν ΦK

-e - =

Kα

hν ΦLΦK -='

Figure A.2

b) Or the photon is absorbed within the atom itself on its way out and ionizes the atom in an outer shell; for example a Kα photon can eject an L, M or N electron; this phenomenon is called the Auger effect. Again, the ionized atom becomes a source of radiation as explained above (Figure A.3). It should also be noticed that because of the Auger effect in the higher levels two or more vacancies could be created. The creation of double vacancies is responsible for the appearance of satellite peaks.

K

L

M

NO

Φ ΦL M- -[ ]Φ

Ke - =

Kα

Figure A.3

ARL 9900 INTELLIPOWER Series User Manual AA83654 A-2


The Auger emission is more probable for low atomic numbers while X-ray emission is more likely for high atomic numbers. The probability that an X-ray photon will be emitted (instead of an Auger electron) is called Fluorescence Yield.

The Figure A.4 shows the fluorescence yield as a function of atomic number. The K lines are more probable than the L lines which explains the difference in the yield for the K and L type transitions. In practical X-ray spectrometry, we use the K lines to measure elements with low to medium atomic number while we switch over to measure L lines for the heavy elements, or even to the M lines.

0 20 40 60 80 100

Atomic number Z

1.0

0.8

0.6

0.4

0.2

0

Fluorescent yield ω

ω

ω

ωK

L

M

Figure A.4



Scattering

Scattering of primary X-rays by the sample results in two processes: Coherent scattering (without loss of energy) and Compton scattering (with a little loss of energy). As mentioned before, not the entire incident X-rays participate in the photoelectric absorption. Some of them do not reach the inner shells and thus they do not give rise to absorption. Instead, they are deflected by the atoms in two ways:

a) The incident X-ray photon is deflected without loss of energy. b) The X-ray photon is deflected with a slight loss in energy and thus with an increase in wavelength.

In a) the sample scatters primary X-rays with exactly the same energy. This scattering is thus called coherent or elastic scattering. In b), as shown in Figure A.5, some of the photons collide with a loosely bound electron in an outer shell of the atom. The electron recoils under the impact and leaves the atom carrying with it some of the energy of the incident photon. Thus the primary photon is scattered with a slightly lower energy. This phenomenon is called Compton scattering. The difference in energy between the incident photon and the Compton photon depends only on the angle (φ) between the unscattered and the scattered X-rays. It is given by the following equation:

∆λ = λ' - λ = h/moc (1-cos φ) = 0.02426 (1- cos φ)

Incident photon

Scattered photon

Recoil electron

E = hv

E' = hv'

= hv - hv'kin

y'

x' x

y

φ

ψ

E

Figure A.5

Thus ∆λ is independent of both X-ray wavelength and the atomic number of the scatterer. On the other hand, the intensity ratio of the coherent to the Compton scattering depends on the atomic number of the scatterer. In practical X-ray spectrometry, we are confronted with scattered X-rays: Coherently scattered X-rays contribute to the background in the X-ray spectra. Since they fall exactly at the same energy as the measured line of a given element, they can't be discriminated in general. Thus background in XRF can largely be attributed to scattering of primary X-rays by the sample. Since heavier elements absorb more and scatter less, the background level in the spectra from heavy elements is almost insignificant. On the other hand, it becomes the limiting factor for measuring light elements at low concentrations.

Again, in practical XRF, this amounts to saying that, if the matrix is heavy, we have less problems with the background. If we are working with light matrices, we should be aware of the high level of background. Compton scattering manifests as broad lines accompanying the K and L lines of the X-ray tube target element. Figure A.6 shows an example of these considerations.



All three spectra have been recorded with a Rh anode X-ray tube. Spectrum a) was measured with a light matrix (Teflon), b) with a medium (Pure Al) and c) with a heavy matrix (Pure Fe). The four lines observed are the Rh Kα and Kβ and the RhCompton Kα and Kβ lines. We notice that the intensities of all four lines

decrease as we go to heavier matrices. On the other hand, the ratio between the coherent and the Compton lines increase as we go to heavier element matrices.

Figure A.6

Transmission

Transmission is the counterpart of absorption. The transmission or absorption of X-rays in the matter can be described by an exponential relation. If Io is the intensity of X-rays (of energy E or wavelength λ) incident

on a sample of thickness t (in cm), then the transmitted X-ray intensity I is given by:

I = Io exp -µρt

♦ µ:mass attenuation coefficient (cm2/g) ♦ ρ:the density of the sample (g/cm3)

The mass attenuation coefficient here refers to a particular wavelength in a given absorber, and is in fact the sum of two coefficients τ and σ, where τ is the mass photoelectric absorption coefficient and σ the mass scattering coefficient:

µtotal = τphoto + (σcoherent +σincoherent)

These coefficients can be found in standard textbooks and general literature. This formulae is quite useful when we need to calculate the thickness of intensity filters, the penetration depth of X-rays in a given sample etc. Attenuation of X-rays by photoelectric absorption and coherent or incoherent scattering is essentially an atomic property. Consequently, the mass coefficients of compounds follow the simple law of weighted average, also called the additivity law. For example, a compound containing the elements i, j, k etc. in the proportions by weight Mi, Mj, Mk etc. has a mass attenuation coefficient µ = ΣMiµi/ΣMi or, in terms of the

weight fractions Ci, Cj, Ck etc. µ = ΣCiµi.



Nomenclature used in XRF

The electrons in an atom do not all follow the same orbit but arrange themselves in well defined shells around the nucleus; these shells are known as K, L, M, N, O, P and Q; the K shell being nearest to the nucleus. Each shell represents an energy level, composed of different sub-levels.

Figure A.7

The K shell has the lowest energy and the Q shell the highest, but it is important to note that the largest energy difference between any two shells is between the K and L shells; the smallest difference is between the outermost shells. The energy of a given electronic shell depends on the atomic number and thus, it varies from element to element. Further details of atomic structure can be obtained from any standard text book of Atomic Physics. X-ray spectral lines are grouped in series: K, L, M, N etc. All the lines in a series result from electron transitions from various higher levels to the same shell.

When a K shell vacancy is filled by an electron from the L shell we get the Kα line radiation, whereas when an electron from the M shell fills this vacancy, we get the Kβ line radiation. Similarly, if a vacancy in the L shell is filled by an electron from the M shell we get the Lα line radiation, if it is filled by an electron from the N shell, we get the Lβ line radiation and if it is filled by an electron from the O shell we get the Lγ line radiation. Every element has its characteristic K, L and M series. Thus, light elements give rise to only K lines, mid range elements can emit both K and L series while the heavy elements produce K, L and M series. Thus the spectra get increasingly complex when we go towards heavier elements. In practical XRF, we select the principle lines of K and L series to measure an element although there may be other lines present. The selection of an analysis line depends mainly on the type of sample, the elements present in it, the concentration range of the elements and the excitation conditions.



Instrumentation

In X-ray fluorescence we basically distinguish between two types of instruments: the wavelength dispersive (WDX) and the energy dispersive spectrometer (EDX). Both WDX and EDX employ an X-ray source for exciting the sample. They essentially differ in the way the X-ray spectra emitted by the sample are detected. In WDX, the fluorescence spectrum is dispersed into discrete wavelengths using a dispersion device (e.g. a crystal) which are then detected using a gas proportional or scintillation counter. In EDX, one measures the entire fluorescence spectrum directly using a solid state detector such as Si(Li) or HPGe which is then processed using a multichannel analyser to obtain the information on an energy scale. The energy and the wavelength of a photon are related in the following way:

E = hv = hc/λ = 12.4/λ

The main components of a WDX spectrometer can be seen in Figure A.10. They are: X-ray tube, primary collimators, crystals, secondary collimators and detectors. Additional components are: Primary beam filters, aperture mask and attenuation filters.

X-ray Tube

The two types of X-ray tubes which have been the subject of considerable discussion in recent years are: End-window and Side-window tubes. Today, all major manufacturers equip their instruments with the End-window tube which proves that this tube is the more versatile and the better compromise for the whole element range. Therefore, the differences in performance and construction will not be discussed here.

The tube houses filament and an anode under a high vacuum metal enclosure. The filament is heated by an electric current which then emits electrons by thermionic emission. These electrons are then attracted and accelerated towards an anode (target) when a high voltage difference (10-70kV) between the anode and the cathode is applied. Primary X-rays are produced when these electrons of high velocity collide with the target material. Upon impact, most of the kinetic energy of the electrons is converted into heat requiring the anode to be cooled efficiently. Only a small part (0.2-0.5% depending on the type of target) of the electron energy is usefully converted into X-rays.

This X-ray radiation consists of the Continuum or Bremsstrahlung or White radiation, the characteristic X-ray lines of the target material (K, L, ... series) and characteristic lines from any contaminants. Thus, as shown in Figure A.8, the primary spectrum from a conventional X-ray tube consists of intense characteristic lines from the anode material (e.g. Rh) on a broad envelop of continuum.

Rh Tube SpectrumK

Kβ

α

Lα

Lβ

Mo Nb Zr

Cl S P

2 3 4 5 61

I

λ0

Continuum

Figure A.8



Continuum

The impact of the electrons on the target is non-selective and produces a wide range of energy transitions and consequently a continuum of X-ray emissions. In other words, stepwise deceleration of the electrons causes a continuum of emission lines.

This continuum has a short wavelength limit which depends on the accelerating voltage used and is independent of the target material. However, the intensity of the continuum increases with atomic number of the target. Figure A.9 shows the intensity of the continuum spectrum at three different voltages for the same target material. We notice that the intensity of the spectrum increases with the voltage and the minimum wavelength limit shifts to lower wavelengths (i.e. higher energies) when we go from 20 to 50 kV.

50 kV

35 kV

20 kV

Inte

nsi

ty

Wavelength

I

λ

Figure A.9

One can express the integral intensity (Iint) of the continuum as a function of the target material (Z, the

atomic number), the high voltage (V) and the current (i) as follows:

Iint is proportional to (i Z V2)

Thus, for a given target and high voltage, the intensity of the continuum is directly proportional to the emission current.

Characteristic spectra and choice of the X-ray tube target

When the incident electrons have sufficient energy to eject electrons from the K and L shells of the target atoms, then one obtains the characteristic K and L lines of the target material. Unlike the continuum, this phenomena is selective and causes intense sharp lines of the given target element. Figure A.8 shows these lines superposed on the continuum. The heavier the element of the target, the more intense the characteristic lines emitted. However, in practice the efficiency of a given target is dependent on the operating conditions (kV and mA).

The X-ray tube target is selected based on several factors. One of the most important factors is related to the efficiency of the target lines to excite a wide range of elements in the sample. In order to understand the efficiency, we must invoke the concept of Absorption Edge of an element. Every element has an absorption edge for a given series of lines. For example, an element like Mo has a K absorption edge and three L absorption edges (LI, LII, LIII). As discussed before, this is related to the binding energy of the electrons in the K shell or L shell. Therefore, when choosing a suitable target element, one must consider the position of the K and L lines of the target. If these intense target lines are close to the absorption edges of the analyte elements in the sample, they make the dominant contribution to the excitation of the sample; otherwise the continuum makes the dominant contribution. Although X-ray tubes are available with different target elements like Cr, Cu, Mo, Rh, Au and W, it is difficult to find a favourable target for all analytes.




Consequently, continuum is frequently relied on for excitation. However, one can optimise the choice of the target element by considering the most common parts of the periodic table. Majority of the spectrometers are equipped with Rh X-ray tubes since, the Rh K lines can excite the mid range elements while the Rh L lines can effectively excite the lighter elements (see Figure A.8). When an analyte contains more frequently medium to heavy elements, W target tubes are selected occasionally.

Spectral Line Interference

The primary spectrum may not only contain the lines from the target element but also those from impurities in the target, contaminants like Fe, Cr or Cu from various parts inside the tube. Consequently, the background level at these elements may be unusually high. Thus, care must be taken to minimise the contaminant lines from the tube. In addition, the target lines scattered by the sample may not permit the analysis of the same element in the sample. Sometimes, primary beam filters are used to filter out the characteristic lines from the tube if the same element is present in the sample or overlapped by a tube line.

Window thickness

X-ray tubes are usually sealed with a beryllium window since beryllium has the lowest absorption for X-rays. The intensity of the low energy X-rays (also referred to as soft X-rays) in the continuum depends strongly on the window thickness. Most standard X-ray tubes are fitted with Be window of 75µ or 50µ. The thinner window is more efficient for the excitation of the light elements. For example, transmission of soft X-rays (useful to excite light elements) improves by at least 20% when the window thickness is reduced from 75µ to 50µ.


Dispersion

A dispersion device is the heart of a WD XRF spectrometer. It contains the following parts: Primary and secondary collimators (flat crystal geometry) or entrance and exit slits (focussing crystal geometry), crystals and detectors. One can classify the XRF spectrometers into two categories depending on the X-rays optics involved.

Sequential Instruments

Traditionally, sequential instruments employ a "Parallel beam geometry" or a "flat crystal geometry" allowing the angles of the crystal and the detector to be selected with a device called goniometer (a rotating frame on which the crystal and detector have a Theta-two Theta coupled movement). The geometry of such a spectrometer with the main components is shown in Figure A.10 and a sketch of our goniometer in Figure A.12.

Sample

X-ray tube

Crystal

Collimator

Detecto

r

Θ

2Θ

Cassette PrimaryChamber

Spectrometer Tank

PrimaryBeamFilter Elliptical

Mask

Anode(Target)

BerylliumShutter

Figure A.10



Simultaneous Instruments

In Figure A.11 the simultaneous type (or fixed channel type) of spectrometer is shown where one makes use of a "Focussing beam geometry". Here, instead of flat crystals, we use curved crystals; the radius of curvature being a function of wavelength range of the spectral lines to be measured. Further, collimators are replaced by slits whose width and height are again determined for each wavelength. This type of configuration is obviously used to measure a predetermined element since all the parameters are fixed based on the wavelength of the spectral line to be measured. Thus, a simultaneous instrument may house as many as 30 such fixed channels, each dedicated to measure one line.

KXx9499D00300

X-ray tube

Focussing crystal

Anode

Sample

Entrance(Source) slit

Exit(Detector) slit

Detector

Figure A.11



Instrument Components

We will now discuss the basic components involved in the wavelength dispersive spectrometer (both sequential and simultaneous types). As mentioned earlier, crystals are the essential part of the spectrometers. In the following discussion, several concepts related to them are presented.

Goniometer

The exact positions of the crystal and detector are read by two optical encoders based on Moiré fringes. This gearless system ensures an accurate and reproducible positioning of crystal and detector as compared to the mechanically coupled (gear) system. Thus, a sequential measurement consists of positioning the crystal at a given Theta and the detector at 2 Theta and counting for certain amount of time. Then the crystal and detector are rotated to a different angle for another line etc.

Detector 2θ angleencoder

Detector

X-ray tube

Primary beam filter

SamplePrimary collimator Crystal

Secondary collimator

2θ Angle

1θ Angle

Crystal 1θ angleencoder

Figure A.12

Thus a goniometer renders qualitative and semi-quantitative analysis of the sample where one has to scan a whole range of wavelength to identify the elements present in the sample. In a quantitative analysis, where the elements present in the sample are known, one can set the crystal and detector on a peak position of the line and count for a fixed time, and then move off the peak to measure background points and subsequent elements. A secondary collimator is placed between the crystal and the detector to guide (collimate) the diffracted beam into the detector and also to limit unwanted radiation getting into the detector.



Collimators

The primary and secondary collimators are usually made of a series of parallel blades. The length and spacing of the blades determine the angular divergence admitted by the collimator. This angular divergence together with the crystal "rocking curve" (the width of the diffraction profile) determine the final resolution of the spectrum. One can improve the resolution by closing the collimators to minimise the divergence. But then, the photon flux across the collimator and hence the intensity decreases.

Sample

Crystal

Primary

Collimator

Intensity

FWHM

2 θ

+ ∆ θ− ∆ θ

Figure A.13

Thus, a compromise between the final resolution (necessary to avoid important spectral overlaps) and the sensitivity (related to the intensity) is made. Generally, the collimators are adopted in accordance with the crystal's intrinsic divergence, which varies from one type of crystal to another. Some of the crystals offer excellent resolution while others have a very wide diffraction profile. For this purpose, our sequential spectrometers offer up to four types of collimators. Fine collimators are used for most of the heavy elements, Medium for the mid range elements and Coarse for the light elements.



Crystals

A crystal may be defined as a solid, composed of atoms arranged in a periodic pattern in three dimensions. In a crystal lattice, the plane in which atoms are in a row is called the crystal plane. The Figure A.14 shows a set of crystallographic planes in a cubic crystal.

The planes are identified using Miller indices (hkl). For example, in the figure are shown three such planes: (100), (110) and (111). The interplanar spacing (the distance between any two adjacent planes of same type) is denoted as d. In XRF, we generally refer to the 2d values of the crystals since we will be using the 2d values in what follows.

100 101

111 201

x

yz

Figure A.14

Diffraction

The crystal planes reflect X-rays just like mirrors reflect light. The main difference is that crystal planes reflect X-rays only when certain conditions are met. This selective reflection is known as diffraction.

λ

d

2d sin θ

d d sin θ

θ

Figure A.15




Diffraction can be considered as constructive interference, in the sense that when the X-ray photons (considered as waves) are reflected coherently, they undergo a constructive superposition of the waves. Only then, the X-rays are reinforced in their amplitudes while in all other cases, they interfere destructively. The most important condition is the so called "Bragg's Law of Diffraction". Bragg's law says that if a lattice plane having an interplanar spacing of d reflects an X-ray wavelength of λ, this wave differs in path length by a distance of (2d sin Θ) from the wave reflected by the adjacent plane. This phenomenon is shown in the Figure A.15. When this path length differs by a whole number of wavelengths, the reflected X-rays are reinforced, otherwise they annul each other. We can sum up this with the following Bragg equation:

nλ = 2d sin Θ Bragg's law

where: n: an integer (1,2,3...) called "Order of Diffraction".

d: interplanar spacing of the crystal plane used (Angstroms).

Θ: Bragg angle or diffraction angle (degrees).

λ: wavelength of the spectral line (Angstroms).

Thus, we see from this relation that for a given crystal plane and for a given order of diffraction, each wavelength in the incident XRF spectrum is diffracted at an unique angle. The maximum wavelength a crystal plane can diffract is 2d itself (when sin Θ takes the maximum value of 1). Therefore, one requires crystals or crystal planes with different 2d values in order to cover different wavelength ranges across the periodic table. A number of crystals suitable for diffraction are available today. Some of them are inorganic (like LiF) while others are organic (like PET) in nature.

Multilayer Structures

As we go from short wavelengths (lines from heavy elements) to long wavelengths (mid range elements), the 2d spacing of the crystal used also increases in order to be compatible with Bragg's law and hence the angular range. However, as we go to very long wavelengths (the K lines from light elements such as Beryllium to Magnesium), we must use crystals with increasing 2d spacing (>10 Angstroms). Most of the natural crystals do not have such high 2d spacings. Historically, some of these light elements were measured with synthetic crystals like lead stearates and some kind of soap crystals which suffered from several drawbacks (radiation damage, stability under vacuum etc.). Today, new stable structures called "Layered Synthetic Microstructures", (in short LSM) are available. These are multilayers of a light element (like B, C ..) and a heavy element (Mo, Ni, V, ..) alternating with a spacing of 2d deposited on a Si substrate.

The advantage with these man made structures is that one can try to optimise the combination of the light and heavy elements, the thickness of the layers, and the 2d spacing in order to get the best possible device for a given element. The result of these new developments is that we now have a family of multilayers allowing one to measure elements from Beryllium through Magnesium. We use essentially three or four types of these multilayers along with the natural crystals.

Reflectivity and Resolution

In addition to having a convenient 2d spacing, the crystals should have good diffraction efficiency, i.e. the ratio of diffracted photons to the incident photons. Some crystals like LiF have excellent reflectivity while others suffer from a poor diffraction efficiency. We are generally interested in the peak reflectivities and not the integral reflectivities. The variation of reflectivity when the crystal is "rocked" around the diffraction peak by small angles is called the "rocking curve" of the crystal. The height and the width of this curve give us the indications on the total/integral reflectivity, the peak reflectivity and the width of the diffraction profile. These characteristics depend on several factors; the most important being the mosaic structure of the crystal. If the crystal is nearly perfect (i.e. no defects in the crystals, no surface damage, no doped impurities etc.), then it will have a very narrow rocking curve and rather weak peak reflectivity. This is attributed to a phenomena called "Self-extinction" in the crystals. Self-extinction is essentially due to the fact that the diffracted waves from the inner planes in the crystal are reflected back into the crystal in the absence of any defects (deviation from perfect periodicity). Thus, most of the crystals used in our spectrometers are treated



to induce a mosaic structure and reduce the effect of self-extinction. Therefore, the diffraction efficiency can be increased by various treatments such as abrading, quenching, elastic bending, impurity-doping and so on. Of course, it must be done in a controlled way in order not to broaden the diffraction profiles. Otherwise, we may have undesirable effects on the resolution. As a general indication, the multilayers, which are pseudo-crystalline structures suffer from very broad diffraction profiles compared to the natural crystals. Finally, it may be remarked that:

♦ Some of the crystals have an unusually high reflectivity at particular wavelengths. InSb crystal is one such example. Although PET crystal is used as a general purpose crystal (on a goniometer) to measure Al, Si, P, S and Cl, the InSb crystal has more than two times the reflectivity for SiKα.

♦ Further, some of the crystals reflect only odd orders of diffraction, i.e. 1st, 3rd, 5th etc. Germanium crystal is an example. It is used for its higher reflectivity to measure P, S and Cl and does not have 2nd order, 6th order ... reflections. This may be an added advantage in cases where we need to suppress higher orders.

♦ Some crystals may emit their characteristic fluorescence. This may be seen in some cases as a high background on the corresponding elements.

Dispersion Power

Crystals also have an important property called "Dispersion power", i.e. the capacity of a given crystal plane to separate the lines most effectively. The dispersion power depends on (1) the 2d spacing of the crystal plane used (2) the Bragg angle and (3) the order of diffraction. This relation is given as follows:

dΘ / dλ = (n/2dcos Θ)

Thus, we see that:

♦ The smaller the 2d spacing, the better the dispersion. ♦ The higher the diffraction angle, the higher the dispersion ♦ And higher orders of diffraction have increasing dispersion.

An example of this relation is shown in the Figure A.16 where the same spectrum has been recorded with three different crystal planes. In this figure three different crystal planes were used: LiF200 (2d = 4.028), LiF220 (2d = 2.848) and LiF420 (2d = 1.802). We notice that the lines are best separated when LiF420 is used. However, the peak intensities drop significantly when we go from LiF200 to LiF220 to LiF420 crystal planes. Thus, one must keep in mind that higher dispersion may sometimes mean lower peak intensities.

The final point is the observation of increasingly poor dispersion when we move towards light elements. Since the 2d spacing increases (inevitably), crystals or multilayers in this range have poorer dispersion.


Figure A.16

Stability

Stability of the crystal is another important factor for a reliable and reproducible measurement. Crystals may undergo changes due to temperature shifts, they may suffer from radiation damage and they may be affected by chemical pollution in the spectrometer. Thus, care must be taken to maintain them at constant temperatures and protect them from being contaminated. Some crystals are more sensitive to temperature changes than others. Essentially, when the temperature changes, the crystal planes, due to thermal expansion, may attain a slightly different 2d spacing. This obviously shifts the Bragg angle for a given wavelength and thus one may not be measuring at the peak position any more.

PET is one of the most sensitive crystals with respect to temperature particularly at higher Bragg angles. Our spectrometers are equipped with thermal stabilization circuits which maintain the spectrometer temperatures within +/-0.5 degrees. In addition, the crystals are maintained at constant temperatures using a local temperature control system. Thus, the peak shifts due to thermal changes are excluded to a great extent.

Higher orders of diffraction

It may be seen from Bragg's law that higher orders of diffraction from heavy elements may superpose on the first order diffraction of lighter elements. For example, first order of P Kα (6.16 Angstrom, second order of Ca Kβ (3.09 Angstrom) and third order of Gd Lα (2.05 Angstrom) will all be diffracted at nearly the same diffraction angle when the same analysing crystal is used since they all satisfy the Bragg's law at the same Θ angle. Thus, superposition of different orders of diffraction can cause some unwanted overlaps. However, as we will see below, most of the modern spectrometers are equipped with a Pulse Height Discriminator (PHD) which analyses only those pulses with an amplitude above a threshold and fall in a given window. Thus, one can reduce the contribution from higher orders by a proper setting of the PHD parameters.




Resume

We will conclude this chapter by summarising the important points:

♦ Wavelength dispersive X-ray spectrometers employ crystals and multilayers for dispersing the polychromatic fluorescence spectrum into monochromatic wavelengths.

♦ Flat crystals are used in conjunction with collimators in sequential spectrometers (single channel) where a scanning mechanism is provided (Goniometer). The crystal and the detector are coupled by a theta-two theta relation. Our goniometer has a gearless mechanism to ensure precise and reproducible positioning of the crystal and detector. The flexibility and the wide scan range available with the goniometer render the sequential instruments versatile and useful for exploratory (qualitative and semi-quantitative) work.

♦ Curved crystals are used in conjunction with slits in the simultaneous (multi-channel) instruments. These channels (or monochromators) can be constructed once the elements (or the lines) are predetermined. The focussing X-ray optics (thus high intensity and excellent resolution) used, the rapidity and the stability of these instruments make them ideal tools for production control and quality control applications.

♦ Both types, flat crystals or curved crystals, diffract X-rays according to the Bragg's law where the wavelength and theta are related uniquely for a given crystal plane.

♦ Different crystals are used for different spectral domains depending on their 2d spacing, dispersion power, reflectivity and stability.

♦ The resolution of a spectrometer is its ability to distinguish two spectral lines of nearly same wavelength or closely spaced lines. In WDX, resolution is a combined effect (convolution) of angular divergence admitted by the collimators or slits, the rocking curve (the width of the diffraction profile) of the crystal, the dispersion power and to a much lesser extent, the detector resolution. Thus, the combination of primary collimator and crystal vary from one spectral region to another. In contrast to the WDX spectrometers, the resolution in EDX spectrometers is predominantly determined by the energy resolution of the detector.


Detection

Detectors used in most of the commercial WDX spectrometers can be classified into two categories:

(1) Gas filled proportional counters for long to intermediate wavelengths (FPC, Multitron and Exatron).

(2) Scintillation counters for short wavelengths.

Gas filled counters

Gas filled detectors are again subdivided into two types: Flow Proportional Counters (FPC) and Sealed Detectors. FPCs have a continuous flow of gas and the pressure inside the detector is regulated. They are generally closed with Aluminium coated thin polypropylene windows of the order of 1-2µ thick. The purpose of such a thin window is essentially to increase the transmission of long wavelength X-rays.

Sealed detectors, referred to as Exatrons and Multitrons, have 25-200 micron beryllium windows. FPC’s are used for light elements (from Beryllium through Copper in general) on a goniometer. Sealed detectors are employed in fixed channels although small size FPCs are used in the fixed channels for light elements. The principle of operation is the same in both the types. The gas detector in its simplest form consists of a hollow metal cylinder (acting as cathode) carrying a filament (metal wire of about 50-75 microns diameter acting as anode). A high voltage is applied across the two electrodes. The cylindrical casing is earthed. The Figure A.17 shows the Multitrons and Exatrons.

Exatron

Multitron

Filament +

Filament +

Body -

WindowBody -

Figure A.17




Primary Ionization

The detectors are filled with rare gases He, Ne, Ar, Kr and Xe are used for this purpose. They are mixed with a quench gas (methane, for example). An X-ray photon entering the detector ionizes the gas and creates an electron-ion pair. The number of electron-ion pairs depends on the type of gas and the energy of the incident photon. As an example, Ar gas requires an effective ionization potential of about 26 eV for one electron-ion pair. Thus, if a Cu Kα photon (wavelength = 1.542 A, energy = 12.4/1.542 = 8040 eV) entered the detector, each photon (also called an event) will produce 304 electron-ion pairs. If a photon with twice this energy enters the detectors, it will (ideally) produce twice the number of pairs. Thus, for a given detector gas, if all the incident photons produce ionized pairs, then the number of pairs is proportional to the energy of the photon. This is why these detectors are called Proportional counters. Thus, if the electrical charges produced are counted, we would have measured the intensity of a given spectral line.

The number of electron-ion pairs produced during the primary ionization process is not sufficiently high to be detectable. One needs to amplify the signals considerably before they can be measured with good signal to noise ratio. This is accomplished by a process called "Avalanche" or "Gas Amplification" and is explained in the next section.

Avalanche

Consider an X-ray photon entering the active volume of the detector. It produces primary electron-ion pairs along its path until all its energy is expended. When the detector is under high voltage, the electrons are pulled towards the filament and the ions are attracted towards the body of the detector. As electrons approach the filament, they are subject to stronger electric field closer to the filament which accelerates them further. As shown in the Figure A.18, when the applied potential is low, the electrons recombine with the positive ions before they reach the anode wire. This is the region of unsaturation. As the applied potential is increased, the recombination is overcome completely and then all the primary electrons reach the anode. Ionization-chambers operate in this region. Since there is no further secondary ionization, the gas gain remains as 1. When the potential is high enough to accelerate the electrons which collide with other gas atoms to initiate secondary ionization, one begins to see a substantial gain in the number of charge carriers. This order of multiplication increases as the electrons approach closer to a few diameters of the anode wire.


100

500 1000 1500 2000 Anode E.H.T. [V]

Num

ber o

f ion

pai

rs

102

104

106

108

1010

Prop

ortio

nal r

egio

n

Gei

ger r

egio

n

Glow discharge

Corona discharge

Avalanche region

A B C D E

Figure A.18

In the proportional-counter region, each primary electron initiates only one avalanche and the avalanches are free of any interaction. Thus the final number of electrons after amplification is still proportional to the number of primary electrons which in turn is proportional to the energy of the photon entering the detector. Most of the detectors used in XRF spectrometers function in the region of proportionality. When the potential is increased beyond this region, the proportionality deteriorates as the same electron may initiate multiple avalanches. When the applied potential is so high that avalanche is generalized, the gas ions and atoms are excited. Secondary electrons may be generated at the anode and electrons may be expelled at the cathode. In other words, one finds a general discharge in the entire detector. Thus, there is no longer any proportionality between the incoming photons and the output pulse of the detector. Geiger-Muller counters operate in this region. Finally, a further increase in the potential triggers a continuous and sustained discharge and the detectors begin to glow. At the end, an arc discharge occurs between the cathode and the anode wire and detector is likely to get destroyed.

In the proportional region, which is of interest here, one attains a gas gain of the order of 105-106 permitting one to obtain good signal to noise outputs. One of the most common gas fillings is the mixture of 90% Ar + 10% CH4 called P10 gas. The purpose of methane addition is essentially to quench the phenomena of avalanche at one stage. The quench gas molecules also get ionized along with the Ar atoms. When they are dispersed in the detector's active volume, they contribute to the recombination of the electrons and ions when the avalanche proceeds in an uncontrolled manner.




Characteristics

Finally, the following properties of the detectors are relevant in practical XRF.

♦ Resolution of the detector is expressed as Resolution = (W / V) x 100 where W is the peak width (of the energy profile) at half-width and V is the maximum of the pulse amplitude distribution.

♦ Stability of the detectors depends on the cleanliness of the anode wire. If the gas-fillings are not pure enough or small particles get deposited on the anode wire, they may distort the local electric field (by changing the effective diameter of the anode wire). This may change the gas gain factor causing unstable detection.

♦ Dead time of the detectors is a more important problem in practical X-ray spectrometry. Dead-time can be defined as the time during which, after a photon has initiated the ionization, the detector can not process the next event. As we have seen above, the incident X-ray photon produces a series of ion-electron pairs which are multiplied in the avalanche process.

The time elapsed between the entry of the photon and the avalanche production may be of the order of 10-

7 seconds. The electrons rapidly move towards the anode while the ions (being heavier) move slowly towards the metal body of the detector. This causes a positive ion sheath around the anode wire which prevents further avalanches to occur until its dissipation. Thus, the detector is said to be dead during this inactive period. In practical terms, this means that the photons entering the detector during the dead time are not counted since the detector has not totally recovered from the previous event. At high counting rates (high photon flux) the loss of counting events can be reasonably high.

Most modern spectrometers correct this loss mathematically. The dead time can be estimated using different photon counting rates. Since the output signal is proportional to the number of photons, any deviation from linearity indicates the extent of dead time.

♦ Escape peaks in the detectors are caused by the X-ray photon whose energy is greater than the absorption edge of the counter gas. For example, if the counter contains Ar gas, some of the photons (say with an energy E from a given element) may induce Kalpha transitions in Ar and lose their energy in the primary process. Thus the pulse amplitude distribution contains not only the pulse amplitude from original photons of energy (E) but also additional pulses with an amplitude corresponding to the difference in the energy E - E(ArKα).

Escape peaks may not represent a serious problem as long as they do not cause overlaps on other lines from the sample. In some cases, the threshold of the pulse height discriminator is fixed such that the escape peaks are not counted at all. This may not be a good practice since the intensity of the escape peak is also contributed by the photons from the same spectral line.


Scintillation Counters

Scintillation counters operate on an entirely different principle compared to the gas filled detectors. They consist of two essential parts: a scintillating material (called phosphor, usually a single crystal doped with an activator) and a photomultiplier. Scintillating crystals like NaI:Tl+ have an interesting property that when the X-ray photons are incident on such a crystal, they emit visible (in the present case, blue) light. Thus, they convert X-ray photons into visible photons. The Figure A.19 shows the construction of a scintillator counter.

D1 D2 D3 D4 D5 D6 D7 D8 D9 D10

Anode

AK

NaI:Tl +

Be window Photocathode

X-ray photon

Dynodes

Pre-ampifier

High voltage

Figure A.19

The scintillator crystal is optically coupled to an appropriate photomultiplier tube and the whole assembly is sealed using a beryllium window. Sealing is necessary because the NaI:Tl+ crystal is hygroscopic in nature and should be protected from humidity. When the blue photons from the scintillator crystals are incident on the photocathode of the PM tube, they release photoelectrons.

The PM consists of a number of positive electrodes called dynodes which are arranged at an increasingly positive potential. Thus the photoelectrons get accelerated successively by the dynodes and release more photoelectrons. Thus, the process of multiplication continues until the last dynode. The end result is an internal amplification of the order of 105-106 depending on the number of dynodes and high voltage applied to the PM tube.

Thus, a scintillator is a solid state detector where X-ray photons are converted into light photons and detected by a conventional photomultiplier. The escape peak phenomena and the dead time are also observed in scintillator detectors. Escape peaks may occur when the incident X-ray photon can eject a K or L shell electron from the iodine in the phosphor material. Dead time of the scintillation counters is somewhat longer than that of the gas proportional counters.



Pulse Height Discriminator (PHD)

Both gas detectors and the scintillation counters used in XRF are proportional detectors, i.e. the energy of the incident X-ray photon determines the size of the voltage pulse produced by the detector. A pulse height discriminator makes use of this property in order to select only a narrow range of voltage pulses, thus rejecting all those unwanted pulses. X-ray photons of different orders of diffraction may enter the detector if their Bragg angles coincide. As shown in the Figure A.20, the height of the pulses from different orders of diffraction is not the same. The pulse height analyser includes adjustable upper and lower electronic thresholds forming a "window". This window only accepts pulses from the detector with amplitudes greater than the lower threshold and smaller than the upper threshold. These pulses can pass through the window into the output amplifier and all others are rejected. Thus, by a proper setting of threshold and window, one can significantly reduce or even eliminate the contribution from higher order diffraction lines. This setting also helps in reducing the background radiation.

Escape-Peak

ElectronicNoise

Threshold Window

Second order peak

First order peak

Energy

Intensity

Pulse A Pulse B

E1 E2 E3 Figure A.20

As shown in the Figure A.21, the incoming pulses A, B are from physically overlapping spectral lines which are seen by PHD to have differing amplitudes. To receive pulse B, the window is adjusted to accept the amplitude E2 - E3; for pulse A the window is set to E1 - E2 when pulse B is too high and is rejected.

E1

E2

E3

Time

Pulse Height (E)

A

B

A

A

Figure A.21




Final output

Finally, the output from the amplifier or pulse height analyser must be interpreted. One uses a scaler, which gives a strict pulse-by-pulse count as received from the pulse height analyser. However, the preferred method is to integrate the pulses as received in an electronic integrator (a scaler and timer). If N represents the number of counts in an integration time of t seconds, then the count rate is simply N/t counts per second (cps). Thus the output signal from the spectrometer is, for most practical purposes, presented in terms of counts per second. This value of intensity is then converted into concentration using different methods (calibration, empirical coefficients method, Fundamental Parameters method etc.). In a qualitative analysis, the intensity (cps) is directly displayed on a screen as the goniometer scans across different Bragg angles, resulting in a spectrum.

User Manual XRF 9900

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