D S Judson UNTF Forum Salford

Outline The Compton imaging process The PORGAMRAYS project What is it? How does it work? Detector description Spectroscopic performance GEANT simulations Experimental Compton imaging performance Summary

) θ γ-ray source E0 E1 x1,y1,z1 E2 x2,y2,z2 Scatters Absorbed Where and E0 = E1 + E2

Cone of possible source location E1 x1,y1,z1 E2 x2,y2,z2 ) θ

Compton imaging process Projection of many cones gives position information Area of greatest overlap gives source location 1 event 100 events10 events

PORGAMRAYS – What is it? Portable Gamma-Ray Spectrometer The project aims to develop a gamma-ray spectrometer that is Handheld and battery operated Able to work at room temperature – no cooling Durable, for use in hostile environments Capable of providing Energy resolution (for isotope identification) Imaging (for location information) Potential applications for this unique sensor include: decommissioning, security and safety monitoring

PORGAMRAYS – How does it work? Good spectroscopic performance at room temperature? – Cadmium Zinc Telluride (CZT) detectors Source location information? – Compton imaging Compton imaging requires good knowledge of the position of the gamma-ray interaction within the detector? – Pixelated detectors Useful over a wide range of energies? - Stack of thin detectors

PORGAMRAYS CZT detectors Dimensions of 20 x 20 x 2 mm Pixelated (10 x 10) 2 x 2 x 2 mm voxels

PORGAMRAYS CZT detectors Dimensions of 20 x 20 x 2 mm Pixelated (10 x 10) 2 x 2 x 2 mm voxels Detector bonded to daughter board Data read out through NUCAM II ASICS [1] Energy range 0f 350 keV [1] P Seller et. al., IEEE Nuclear Symposium Conf. Rec., V6, 3786, ‘06

PORGAMRAYS – The solution Compton imaging using a stack of thin pixelated CZT detectors 6 or 7 detectors Modular ASIC readout Energy range 60 – 2000 keV

The PORGAMRAYS demonstrator Two CZT detectors Running from external power supplies Mechanically damped housing to avoid microphonics problems

Spectroscopic performance of CZT At 60 keV ( 241 Am), FWHM ~ 6 keV, noise ~ 20 keV

Geant4 simulations Simulated two CZT detectors with 5 mm separation Two different gamma-ray energies were 121 and 356 keV Spectroscopic and imaging data used to evaluated the potential of the device

Geant4 simulations 121 keV γ-rays deposit little energy in the scatter detector Scatterer Absorber Eγ (keV) Eγ (keV)

Geant4 simulations 356 keV γ-rays deposit keV in each detector Scatterer Absorber Eγ (keV)

5 keV energy resolution, 2 mm position resolution Source located at x = 110 mm y = 110 mm FWHM X = 25 mm FWHM Y = 24 mm 15 keV energy resolution, 2 mm position resolution (356 keV) Compton images - simulated x (mm) y (mm)

Compton images – real data Source located at x = 100 mm y = 115 mm Point source 40 mm from the scattering detector’s surface FWHM ~ 25 keV x (mm) y (mm)

Compton images – real data x (mm) y (mm) Source located at x = 97 mm y = 100 mm Point source 40 mm from the scattering detector’s surface FWHM ~ 25 keV

Possible to resolve changes in source position of only a few mms Compton images – real data x position (mm) x = 100 mm x = 115 mm

5 keV energy resolution, 2 mm position resolution Simulated Real Simulated V’s real images

Conclusions A CZT based Compton camera has been developed Energy resolution of ~ 10 % at 60 keV Imaging algorithm have been developed and employed Image resolution of ~ 20 mm FWHM has been demonstrated Changes in position of ~ 10 mm can easily be resolved Geant simulations have been performed and validated

Funded jointly by the EPSRC and TSB

Collaborators A J Boston 1, P J Coleman-Smith 2, D M Cullen 3, A Hardie 4, L J Harkness 1, L L Jones 4, M Jones 1, I Lazarus 2, P J Nolan 1, V Pucknell 2, S V Rigby 1, P Seller 4, J Simpson 2, M Slee 1 1 The University of Liverpool 2 STFC Daresbury Laboratory 3 The University of Manchester 4 STFC Rutherford Appleton Laboratory

Fold 1 events Fold 2 events added back Spectroscopic performance of CZT γ γ

5 keV energy resolution, 2 mm position resolution FWHM Z = 20 mm Image resolution – z plane