Transcript Compton Imaging with the PorGamRays Detector

D S Judson
UNTF Forum 2010 - Salford
Outline
 The Compton imaging process
 The PORGAMRAYS project
 What is it?
 How does it work?
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
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Detector description
Spectroscopic performance
GEANT simulations
Experimental Compton imaging performance
Summary
E1
cos  1 
 ( E 0  E1)
Scatters
Absorbed
E2
x2,y2,z2
θ
E1
x1,y1,z1
me c 2
Where  
E0
and E0 = E1 + E2
γ-ray
source
E0
E1
cos   1 
 (E0  E1)

θ
E2
x2,y2,z2
E1
x1,y1,z1
Cone of
possible
source
location
Compton imaging process
 Projection of many cones gives position information
 Area of greatest overlap gives source location
1 event
10 events
100 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 (241Am), 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
0
20
40
60
80
100 120
Eγ (keV)
Eγ (keV)
140
160
180
Absorber
200
Geant4 simulations
356 keV γ-rays deposit 140-220 keV in each detector
Scatterer
0
50
100
150
200
250
Eγ (keV)
300
350
Absorber
400
Compton images - simulated
15
5 keV
keVenergy
energyresolution,
resolution,22mm
mmposition
positionresolution
resolution (356 keV)
y (mm)
Source located at
x = 110 mm
y = 110 mm
FWHM X = 25 mm
FWHM Y = 24 mm
x (mm)
Compton images – real data
y (mm)
Source located at
x = 100 mm
y = 115 mm
Point source 40 mm
from the scattering
detector’s surface
x (mm)
FWHM ~ 25 keV
Compton images – real data
y (mm)
Source located at
x = 97 mm
y = 100 mm
Point source 40 mm
from the scattering
detector’s surface
x (mm)
FWHM ~ 25 keV
Compton images – real data
Possible to resolve changes in source position
of only a few mms
x = 115 mm
x = 100 mm
x position (mm)
Simulated V’s real images
5 keV
Simulated
energy resolution, 2 mm position resolution
Real
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 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 Liverpool
2 STFC Daresbury Laboratory
3 The University of Manchester
4 STFC Rutherford Appleton Laboratory