D S Judson

UNTF Forum 2010 - Salford

OutlineThe Compton imaging processThe PORGAMRAYS project

What is it?How does it work?

Detector descriptionSpectroscopic performanceGEANT simulationsExperimental Compton imaging performanceSummary

)θ

γ-ray source E0

)10(

11cos

EE

E

E1x1,y1,z1

E2x2,y2,z2

Scatters

Absorbed0

2

E

cmeWhere

and E0 = E1 + E2

Cone of possible

sourcelocation

cos 1 E1

(E0 E1)

E1x1,y1,z1

E2x2,y2,z2

)θ

Compton imaging processProjection of many cones gives position

informationArea of greatest overlap gives source

location1 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 operatedAble to work at room temperature – no coolingDurable, 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 detectorsDimensions of 20 x 20 x 2 mmPixelated (10 x 10) 2 x 2 x 2 mm voxels

PORGAMRAYS CZT detectorsDimensions of 20 x 20 x 2 mmPixelated (10 x 10) 2 x 2 x 2 mm voxelsDetector bonded to

daughter boardData 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 solutionCompton imaging using a stack of thin pixelated CZT detectors

6 or 7 detectorsModularASIC readoutEnergy range

60 – 2000 keV

The PORGAMRAYS demonstrator

Two CZT detectorsRunning from external

power suppliesMechanically damped

housing to avoid microphonics problems

Spectroscopic performance of CZTAt 60 keV (241Am), FWHM ~ 6 keV, noise ~

20 keV

Geant4 simulations

Simulated two CZT detectors with 5 mm separationTwo different gamma-ray energies were 121 and 356

keVSpectroscopic and imaging data used to evaluated

the potential of the device

Geant4 simulations121 keV γ-rays deposit little energy in the

scatter detectorScatterer

Absorber

Eγ (keV)0 20 40 60 80 100 120 140 160 180 200

Eγ (keV)

Geant4 simulations356 keV γ-rays deposit 140-220 keV in each

detectorScatterer

Absorber

0 50 100 150 200 250 300 350 400

Eγ (keV)

5 keV energy resolution, 2 mm position resolution

Source located atx = 110 mmy = 110 mm

FWHM X = 25 mmFWHM Y = 24 mm

15 keV energy resolution, 2 mm position resolution (356 keV)

Compton images - simulated

x (mm)

y (m

m)

Compton images – real dataSource located at

x = 100 mmy = 115 mm

Point source 40 mm from the scattering detector’s surface

FWHM ~ 25 keV

x (mm)

y (m

m)

Compton images – real data

x (mm)

y (m

m)

Source located at

x = 97 mmy = 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 resolutionSimulated Real

Simulated V’s real images

ConclusionsA 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 Boston1, P J Coleman-Smith2, D M Cullen3,

A Hardie4, L J Harkness1, L L Jones4, M Jones1,

I Lazarus2, P J Nolan1, V Pucknell2, S V Rigby1,

P Seller4, J Simpson2, M Slee1

1 The University of Liverpool2 STFC Daresbury Laboratory

3 The University of Manchester4 STFC Rutherford Appleton Laboratory