Combining the strengths of UMIST andThe Victoria University of Manchester

A prototype X-ray imaging system using pixelated energy resolving detectors

A prototype X-ray imaging system using pixelated energy resolving detectors

Conny Hansson,

Supervisor: Prof. Robert. J. CernikFunded by EPSRC

Materials Science Centre

University of Manchester

Combining the strengths of UMIST andThe Victoria University of Manchester

Groups

Advanced Characterization Techniques GroupSchool of Materials, University of Manchester

The development of the rapid tomographic energy dispersive diffraction imaging system, rTEDDI for short.

The HEXITEC consortium (www.hexitec.co.uk)

A collaboration between Manchester University, Durham University, Surrey University, Birkbeck College and the Rutherford Appleton Laboratory

The development of materials, interconnection technology and readout for imaging CdZnTe detectors

Combining the strengths of UMIST andThe Victoria University of Manchester

• What is rTEDDI

• Limiting factors of the current rTEDDI system

• The ERD2004 detector

• Measurements and Results

• Consequences of the results and the development of the HEXITEC detector

Combining the strengths of UMIST andThe Victoria University of Manchester

What is rTEDDI ?

Combining the strengths of UMIST andThe Victoria University of Manchester

- Tomographic Energy Dispersive Diffraction Imaging

gWhite X-ray beam from lab or SR source

Single Voxel TEDDI

Disadvantages: Long exposure times (exceeding16-20Hrs)

(a) polymer test disc (b) 42 mm concrete block (c) Cs in the water supply

(h) Mo-catalyst + ceramic

(i) supercritical synthesis

110

004

disc tomograph [dolomite] block [Ca(OH)2] [calcite] Cs-fluorescence

(d) industrial flow tube (e) drug processor (f) ferrite transformer (g) cement block

Mo-fluorescnece Al2O3-311 r.p.m: 300 400 schematic [CeO2]

unit cell variations(8.43-8.53 Å)

[Ca(OH)2]

[CaCO3]

Examples of 3d TEDDI images

Barnes et al (Birkbeck) Cernik et al (Manchester)

Combining the strengths of UMIST andThe Victoria University of Manchester

rTEDDI realised

2q

MK 1.2 Collimator

Si D

etec

tor

Sample

Sample holder and moving stage

White beam

Thin fan beam

MK1.2

Femto-second laser drilled W collimator array coupled with a pixelated (300µm pitch) energy resolving detector (ERD2004)

L. Tunna, P. Barclay, R.J. Cernik, K.H. Khor, W. O’Neill, P. Seller, Meas. Sci. Technol. 17 (2006) 1767-1775.

P. Seller, W.J. Gannon, A.D. Holland, G. Iles, B.G. Lowe, M.L. Prydderch, S.L. Thomas, R. Wade, SPIE, EUV, X-ray and Gamma-ray Instrumentation for Astronomy IX, San Diego, CA, USA, (1998) July, vol. 3445.

Combining the strengths of UMIST andThe Victoria University of Manchester

rTEDDI: proof of concept

Obtained at Stn. 7.6 SRS Daresbury Labs. For thin samples

R.J. Cernik, K.H. Khor, C. Hansson, J. of the Royal Soc. Interface 5 (2007) 477-481.

Useful areas: strain distribution scanning

material identification (spatially resolved)

Combining the strengths of UMIST andThe Victoria University of Manchester

Limiting factors of the current rTEDDI system

Combining the strengths of UMIST andThe Victoria University of Manchester

Current limitations

X-ray photon detection efficiency

Photon energy (keV)50 100 150 200 250 300 350 400 450 500

Det

ectio

n E

ffici

ency

(%

)

1

10

100

SiGaAsCdTeHgI2TlBr

Calculated for 500m thick material

X-ray photon detection efficiency

Photon energy (keV)50 100 150 200 250 300 350 400 450 500

Det

ectio

n E

ffici

ency

(%

)

1

10

100

SiGaAsCdTeHgI2TlBr

Calculated for 500m thick material1. rTEDDI is currently limited to thin samples due to the low detection efficiency of Si at energies above ~20keV

2. Any pixelated detector used in the rTEDDI system must be able to handle high countrates (1000-10 000 ((hits/pixel)/second) for higher flux beamstations.

Combining the strengths of UMIST andThe Victoria University of Manchester

The ERD2004 detector

P. Seller, W.J. Gannon, A.D. Holland, G. Iles, B.G. Lowe, M.L. Prydderch, S.L. Thomas, R. Wade, SPIE, EUV, X-ray and Gamma-ray Instrumentation for Astronomy IX, San Diego, CA, USA, (1998) July, vol. 3445.

Combining the strengths of UMIST andThe Victoria University of Manchester

SCH04 SCH04MAC04

Pre-Amp Shaper Peak H. Comp.

MAC04 SCH04

Crystal bump bonded to 16x16 array of pre-amplifier (MAC04).

MAC04 wire bonded to two 1x128 arrays of shaping, peak hold and comparator circuits (SCH04).

The ASIC is read out using a DAQ system consisting of a NI card controlled by software written in the LabVIEW environment

Structure and reset schemes of the ERD2004

Combining the strengths of UMIST andThe Victoria University of Manchester

Measurements and Results

Combining the strengths of UMIST andThe Victoria University of Manchester

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000Am Spectrum 300K 300V

Energy (keV)

Num

ber

of

Incid

ents

Np daughters

Am-241

Cd&Te escape peaks

In order to increase the energy range efficiency of the detector the 300µm Si crystal was substituted for a 2mm thick CZT crystal

Flood Field irradiation setupSpectral response of EDR2004 using CZT to flood field irradiation irradiation by a Am-241 dial source

Substituting Si for CZT

Combining the strengths of UMIST andThe Victoria University of Manchester

Deadtime as a function of Clocking Frequency, T=150, for the ERD detector

0

10

20

30

40

50

60

70

80

90

100

0 50000 100000 150000 200000 250000 300000 350000

Clocking Frequency (Hz)

% D

eadt

ime

Countrate measurements

Deadtime measurements (T reset measurement)

Conclusions: DAQ system prevents the clocking frequency needed to obtain countrate requirements of rTEDDI

Countrate limitations

Combining the strengths of UMIST andThe Victoria University of Manchester

CP

CP-1

CP+1

CP+7

CP+8

CP+9

CP-9

CP-8

CP-7

Charge sharing correction tests

• Addition: Highest energy value pixel of the two is awarded the full charge and set as the central pixel for comparison with next event pixel. The lowest value pixel is set to zero.

• Discrimination: All charge shared events are set to zero.

By targeting “simultaneous” hits on neighbouring pixels two charge sharing correction scripts where developed and compared

Combining the strengths of UMIST andThe Victoria University of Manchester

Charge sharing correction tests

10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000Am Spectrum fully Calibrated

Energy (keV)

Num

ber

of

Incid

ents

Pedestals Removed Only

Charge Sharing RemovedCharge Sharing Adding

Conclusion: Charge sharing correction has poor result on this detector. Addition which is the ideal correction for rTEDDI since it does not “throw away events” is not valid due to the electronic cut-off

Combining the strengths of UMIST andThe Victoria University of Manchester

As a consequences of the ERD performance we have designed a specific ASIC for HEXITEC

Combining the strengths of UMIST andThe Victoria University of Manchester

HEXITEC Detector developed:

• Clocking frequency of 5Mhz

• Rolling shutter read-out (no electronic cut-off)

• Receiving prototype Sep.

The HEXITEC detector and further work

First experiments to run the rTEDDI system on thick samples using a high energy station in the beginning of next year

MTPVT grown CZT available from Durham University at the end of the year.