Post on 29-Dec-2015
description
DEVELOPMENT OF MCA (FLASH-ADC/FPGA
BASED) FOR GAMMA SPECTROSCOPY
STUDENT : BÙI TUẤN KHẢI
ADVISOR : MSc. NGUYỄN QUỐC HÙNG
REVIEWER: MSc. LÊ CÔNG HẢO
UNDERGRADUATE THESIS
UNIVERSITY OF SCIENCE - HO CHI MINH CITY
FACULTY OF PHYSICS AND ENGINEERING PHYSICS
DEPARTMENT OF NUCLEAR PHYSICS
OUTLINE
MCA (Flash-ADC/FPGA)
LabVIEWTM interface
Evaluation of MCA
NaI(Tl) gamma spectroscopy
Conclusions and Proposals
Introduction and Motivation
INTRODUCTION & MOTIVATION
Flash-ADC and FPGA technology have been applied in nuclear
experiments and aimed some better results in comparison to
traditional analog chain (CAEN, Nomachi’s group, etc.).
Module Flash-ADC/FPGA has been developed since 2010 by
BSc. Nguyễn Thành Trực, MSc. Lê Thành Nhiệm and MSc. Nguyễn
Quốc Hùng for cosmic ray spectroscopy and HPGe spectroscopy.
For development of MCA (Flash-ADC/FPGA based) for higher dose
rate gamma spectroscopy using NaI(Tl) 3inch x 3inch, MCA is sped
up by using a Histogram Memory.
1
The Gaussian shape pulse from amplifier is the input of multichannel analyzer (MCA).
In commercial MCA (or a PHA), a pulse height is the only concerned information to
build up a histogram.
With modern developed techniques (of ADC), shape of pulse is recorded to calculate
charge integration of pulse.
2
RADIATION SPECTROSCOPY
Pulse
height
U (
mil
iVo
lt)
t (microsec)
CI = Ui
N
i=1
Ui
MCA
Detector Pre-Amp Amp (Pulse Height Analyzer -
PHA)
Display
ADC Control
Logic Memory
MCA (Pulse Charge Integration Analyzer - PCIA)
MCA USING Flash-ADC/FPGA
MCA (Flash-ADC/FPGA) LabVIEWTM inteface
The development of MCA based on Flash-ADC/FPGA board is to write a VHDL code
for embedded FPGA chip.
Development of computer LabVIEWTM interface for triggering and data taking.
3
RS-232
Multichannel Analyzer
Detector Pre-Amp Amp Flash-
ADC FPGA
Computer
LabVIEW
interface
RS-232
Multichannel Analyzer
Detector Pre-Amp Amp Flash-ADC FPGA LabVIEW
interface
MCA (Flash-
ADC/FPGA)
Flash-ADC
FPGA
RS-232
FPGA
chip
Flash-ADC:
• Digitize analog signals
• Speed: 250MHz
• Resolution: 8-bit
• Voltage dynamic range: 1000mV
FPGA:
• Figure pulse height
• Figure pulse charge integration
• Build up Histogram Memory
• Transmit Histogram Memory to
computer
VHDL code developed in 2010 by MSc. Nguyễn Quốc Hùng makes FPGA computes
precise tasks of MCA (trigger, pedestal, height of pulse, integration of pulse).
In this thesis, VHDL code is modified to build up a Histogram by charge integration of
pulse right inside FPGA chip and separately transmits Histogram’s information to
computer 4
Embedded VHDL code to write data into Histogram Memory
5
Embedded VHDL code to read data from Histogram Memory
6
LabVIEWTM
interface RS-232
Multichannel Analyzer
Detector Pre-Amp Amp Flash-ADC FPGA LabVIEW
interface
1 2 3 4
5 6 7 8
9
10
11
12
14
15
13
Channels
Counts
• Interact directly with FPGA.
•Control trigger, size of buffer,
time to measure.
•Presents number of events,
spectrums, pulses (as digital
oscilloscope).
•Save data into file.
7
Saved data can be used to analyze or present spectrum by
familiar software (Genie 2K, Origin)
LabVIEWTM interface
Evaluation of MCA and
gamma spectroscopy using NaI(Tl) 3inch x 3inch
• Evaluation of MCA (Flash-ADC/FPGA) by using
pulse generator
– Time response (dead-time)
– Linearity of MCA (Flash-ADC/FPGA)
• Evaluation of gamma spectroscopy using NaI(Tl) 3inch x
3inch
– Energy calibration (linearity of gamma spectroscopy)
– Energy resolution 8
Evaluation of MCA by using pulse generator
9
Pulse generator generates square pulses with different
widths and frequencies, controlled by users.
Square pulses are shaped by amplifier and become
Gaussian shape.
Shaped pulses are fed into (Flash-ADC/FPGA) with
stable amplitudes and frequencies.
Pulse generator
RS-232
Digital Oscilloscope for monitoring
Pulse
Generator Amplifier
MCA
(Flash-ADC/
FPGA)
Computer
LabVIEW
interface
• For time response, frequency: 12Hz to 12207Hz.
• For linearity of MCA, amplitude: 51mV to 1000mV
• Time of measurement is 100 seconds.
Fig.3.1. Diagram of experiment layout with pulse generator
TIME RESPONSE
11
Frequency
(Hz)
Events/sec
(sec-1)
12 12.05
24 24.09
48 48.17
95 96.33
191 192.65
381 385.29
763 770.57
1526 1541.12
3052 3082.24
6104 3082.24
12207 4109.96
Table 3.1. DAQ speed of MCA
Fig.3.2. Graph of DAQ of MCA
3052 events/sec
547 events/sec
• 5.6 times faster than previous VHDL code:
3052 events/sec compared with 547 events/sec.
• The MCA detects pulses in frequency of 3kHz
without dead-time.
LINEARITY OF MCA (FLASH-ADC/FPGA)
14
Fig.3.4. Linear fit of amplitudes and
located channels
• We investigate amplitude in voltage dynamic range of Flash-ADC: 51mV to1000mV
• Linearity of MCA is good with R-square = 0.99994
Fig.3.3. Spectrum of peaks with varied
amplitudes
R-square = 0.99994
Gamma spectroscopy using MCA and NaI(Tl) 3” x 3”
To figure to responses of gamma spectroscopy using MCA (Flash-ADC/FPGA)
and NaI(Tl) 3inch x 3inch.
METHODE:
• RI sources: 133Ba (0.1μCi) and 152Eu (1.05μCi)
• Time of measurement: 1000 seconds.
• Set up experiments to get spectrums.
Estimate energy calibration, energy resolution.
15
RS-232 MCA
(Flash-ADC/
FPGA)
Computer
LabVIEW
interface
Detector
NaI(Tl) Pre-Amp Amp
Fig.3.5. Diagram of Experiment layout with gamma spectroscopy
Gamma spectroscopy using MCA and NaI(Tl) 3” x 3”
16
Fig.3.6. Spectrum of 152Eu
Fig.3.7. Spectrum of 133Ba
791342 events
726745 events
Spectrums of 152Eu and 133Ba contains energy
peaks varied from 36.6 keV to 1.4 MeV.
17
Table 3.9. Detected energies
Energy (keV) Channel
80.10 143
121.78 220
244.70 462
302.90 572
344.28 653
356.00 677
778.90 1503
964.08 1830
1085.90 2096
1408.00 2650 Fig.3.8. Graph of energy calibration
ENERGY CALIBRATION
E(keV) = (1.958 ± 4.738) + (0.524 ± 0.003) × Ch, R−square = 0.99982
Measured energy is in range of 2.1 MeV
18
ENERGY RESOLUTION Resolution(%) =
FWHM
Meanx100
Radioisotopes Energy (keV) Channel FWHM R (%) R-square
152Eu
121.78 220 27.9 12.6 0.972
244.70 462 43.3 9.4 0.971
344.28 654 54.8 8.4 0.990
778.90 1503 85.3 5.7 0.905
964.08 1830 91.0 4.9 0.890
1085.90 2096 126.1 6.0 0.964
1408.00 2650 133.3 5.0 0.954
133Ba
80.10 143 25.6 17.9 0.98
302.90 572 43.2 7.6 0.976
356.00 677 57.1 8.4 0.996
Table 3.11. Obtained results of Gaussian fit
19
ENERGY RESOLUTION
Fig.3.9. Graph of energy resolution
964.08 keV: 4.9%
1085.90 keV: 6.0%
Resolution at energy of
1MeV is about 5%-6%.
SUMMARY
Using Histogram Memory in VHDL code achieved some goals in experiments with
pulse generator and gamma spectroscopy using NaI(Tl).
• Experiments with pulse generator:
o 5-6 times faster than the old VHDL code (3052 events/s compared with 547 events/s)
In comparison with commercial MCAs, speed of MCA (Flash-ADC/FPGA) is too
slow and can be used for low dose-rate experiments.
o Good linearity
o Suitable parameters to reduce the loss of events.
• Experiments with gamma spectroscopy:
o E(keV) = (1.958 ± 4.738) + (0.524 ± 0.003) × Ch, R−square = 0.99982
o Measured energies are in range of 2.1 MeV.
o Resolution is quite good.
20
PROPOSALS
• Other transmission cables with higher speed should be concerned. USB
cable with speed of 480MBytes/sec should considered (speed of RS-232
cable is 115200 bits/sec).
• Other experiments (efficiency, dead-time, etc.) should be carried out to
find all responses of a gamma spectroscopy using MCA (Flash-
ADC/FPGA).
21
THANK YOU FOR
YOUR ATTENTION
Am
pli
tud
e
Ch
ann
els
Time bin
Single
datum
Digitized pulse signal
Am
pli
tud
e (
V)
Time bin
Trigger level
Trigger rising edge
Am
pli
tud
e C
han
nel
s
Elements
(Time bin)
Storing in buffer
1
2
3
max = datum(pointer)
posi_max = pointer
pointer = 0
max = 0
datum(pointer) >
max
TRUE
FALSE
TRUE
pointer = pointer + 1
pointer =
[size of buffer]
Integration process
FALSE
Integration
of Pulse
Am
pli
tude
Chan
nel
s
Elements in Buffer
(Time bin)
Height of
Pulse
Left Peak
Right Peak
FALSE
posi_max - L
< pointer <
posi_max + R
sum = sum + datum(pointer)
pointer = pointer +1
pointer = 0
sum = 0
pointer =
[size of buffer]
Storing in HM
TRUE
FALSE
TRUE
25
Reset HM
Reading process
Update latest data Update data
continuously
stop = ‘0’ TRUE FALSE
Apparatus Parameters Value
Canberra 2026 amplifier
Coarse gain 20
Fine gain 5-1.0
Shaping time
LabVIEW spectrum interface
Time to stop 100sec
Left Peak
Right Peak 25
Number Data Out 150
Delay 60
Time bin 94
6μsec15
“freq” Frequency
(Hz) “freq”
Frequency
(Hz)
0 12500000 11 6104
1 6250000 12 3052
2 3125000 13 1526
3 1562500 14 763
4 781250 15 381
5 390625 16 191
6 195313 17 95
7 97656 18 48
8 48828 19 24
9 24414 20 12
10 12207
Table A. Variable “freq” and frequency generated
by pulse generator
6
(freq+1)
25 . 10Frequency (Hz) =
2