Download - Compton imaging with the PORGAMRAYS detector
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