Download HPGe detector

Applying γ-imaging techniques
to
nuclear physics experiments
César Domingo Pardo
GSI Helmholtzzentrum fuer Schwerionenforschung
Talk for the visit of the Saudi Arabia delegation to GSI
GSI, Darmstadt
17.08.2009
Outline
• Why position sensitive γ-detectors with radioactive ion beams?
• 3D position sensitive HP Ge detectors
• Characterization of position sensitive HP Ge detectors
In flight/decay γ-ray Spectroscopy
production
selection
86Kr
identification
implantation
Bρ - ∆E - Bρ
spectroscopy
9Be
35m
Primary
Target
Degradador
A Bρ e
=
Q βγ cu
x4 − V2 x2
)
Bρ = Bρ 0 (1 −
D2
56Zn
γ-ray Spectroscopy with 3D-position sensitive HPGe detectors
In flight γ-ray spectroscopy
HISPEC
Advanced
GAmma
Tracking
Array
Efficiency: 43% (Mγ =1) 28% (Mγ =30)
P/T:
58% (Mγ=1) 49% (Mγ=30)
Angular resolution: ~1º
FWHM (1 MeV, v/c=50%) ~ 6 keV
Decay γ−ray spectroscopy after implantation
DESPEC
γ-ray Spectroscopy with 3D-position sensitive HPGe detectors
In flight γ-ray spectroscopy
∆θ
1− β 2
Eγ = E
1 − β cosθ
0
γ
β = 0.5
θ
Via tracking it becomes
possible to determine
the incident angle and
preserve the good
energy resolution.
Decay γ−ray spectroscopy after implantation
Cuentas
Eγ = 1.3 MeV
FWHM = 5 keV
FWHM = 12 keV
FWHM = 35 keV
Energía
γ-ray Spectroscopy with 3D-position sensitive HPGe detectors
In flight γ-ray spectroscopy
θ
Mediante tracking es
posible determinar el
angulo de incidencia y
preservar la resolucion
energética.
Decay γ−ray spectroscopy after implantation
Background and P/T
can be improved by
applying imaging
techniques.
S. Tashenov, et al. NIMA 586 (2008) 224-228
HPGe detector
7 cm
9 cm
HPGe detector
HPGe detector: working principle
HPGe detector: working principle
E = -V V
+ HV = 4000 Volts
HPGe detector: working principle
E = -V V
γ-ray
+ HV = 4000 Volts
HPGe detector: working principle
E = -V V
γ-ray
+ HV = 4000 Volts
electrons
holes
HPGe detector: working principle
E = -V V
γ-ray
+ HV = 4000 Volts
electrons
holes
Electric signal
HPGe detector: working principle
E = -V V
γ-ray
+ HV = 4000 Volts
electrons
holes
Electric signal
HPGe detector: working principle
E = -V V
γ-ray
+ HV = 4000 Volts
electrons
holes
Electric signal
HPGe detector: position sensitivity
E = -V V
γ-ray
+ HV = 4000 Volts
electrons
holes
Electric signal
HPGe detector: position sensitivity
E = -V V
γ-ray
+ HV = 4000 Volts
electrons
holes
Electric signal
Method to characterize the pulse shape in HPGe detectors
Determine a data-base of pulse shapes S(x,y,z) which allows one to correlate an
arbitrarily measured pulse, with an interaction position inside the detector.
How to do this?
Using PET principle in combination with imaging techniques
Method to characterize the pulse shape in HPGe detectors
PET approach using a high performance γ-camera
Features:
• Estimated time 20h
HPGe-Detector
2D γ-camara
• Precision: 1-2 mm
• Imaging
Requisites:
511 keV
22Na
Data group “A)”
511 keV
• Excelent resolution ∆x/x
• Large field of view
Data group “B)”
χ2(Ai,Bi)
Method to characterize the pulse shape in HPGe detectors
PET approach using a high performance γ-camera
Features:
• Estimated time 20h
HPGe-Detector
2D γ-camara
• Precision: 1-2 mm
• Imaging
Requisites:
511 keV
22Na
Data group “A)”
511 keV
• Excelent resolution ∆x/x
• Large field of view
Data group “B)”
χ2(Ai,Bi)
Method to characterize the pulse shape in HPGe detectors
HPGe-Detector
2D γ-camera
511 keV
Hamamatsu R2486
511 keV
22Na
XA,XB,YC,YD
Centroid of the scintillation light distribution
Position X,Y
RMS
Width of the scintillation light distribution
Depth of Interaction (DOI)
Resolution
2 mm
Field of view
7 cm2
Method to characterize the pulse shape in HPGe detectors
IMAR (Individual Multi Anode Readout) techique
HPGe-Detector
2D γ-camera
511 keV
16 Y
16 X
Anodes X
Anodes Y
22Na
511 keV
Nuevo método experimental para la caracterización de
detectores de HPGe
Técnica IMAR (Individual Multi Anode Readout)
Linealidad
Anodos X
UFV = 7cm2
20 cm2
Anodos Y
Resolución Espacial 2mm
0.945 +/- 0.08 mm
Nuevo método experimental para la caracterización de
detectores de HPGe
Técnica IMAR (Individual Multi Anode Readout)
Linealidad
Anodos X
UFV = 7cm2
20 cm2
Anodos Y
Resolución Espacial 2mm
0.945 +/- 0.08 mm
Nuevo método experimental para la caracterización de
detectores de HPGe
Tecnica IMAR (Individual Multi Anode Readout)
2D γ-camara
Paper accepted by IEEE-Transactions on Medical Imaging
HPGe-Detector
Position calibration
• Determine: Xr(xm,ym), Yr(xm,ym)
Gamma-ray
scattering technique
00 position
Grid raw image when it is
parallel to PSD surface (0deg)
Position calibration
(xm,ym) =(4.31,4.30)
M
f'(xm,ym) =
∑C
j =1
f j' ( x m , y m )
j
N
g'(xm, ym) =
∑D g (x
j =1
j
'
j
m
, ym )
Calibration made from all data taken
at multiple planes
Position calibration
400 position
DSG x r cos(θ )
x =
DSG − x r sin(θ )
'
r
y =
'
r
DSG
y r DSG
− x r sin(θ )
Position calibration
400 position
Detector Scan (Test Measurement)
Front view (0 deg):
Side view (90 deg):
Detector Scan (Test Measurement)
Front view (0 deg):
Side view (90 deg):
Detector Scan: Data Analysis
Experimental Validation of the method
Summary & Outlook
• We have developed a γ-camera with spatial resolution, linearity and field of view substantially
improved with respect to similar existing devices
• Our system uses conventional NIM and VME electronics, which makes it not optimal for medical
applications. However, this problem could be overcomed by means of a new acquisition system
based on ASIC, FPGA, etc technologies.
• Applications with thicker scintillation crystals (1 cm) may become possible, without compromising
its good performance, thanks to the more accurate measurement of the DOI. (Tests are in
progress).
6 cm
Summary & Outlook
• We have developed a γ-camera with spatial resolution, linearity and field of view substantially
improved with respect to similar existing devices
• Our system uses conventional NIM and VME electronics, which makes it not optimal for medical
applications. However, this problem could be overcomed by means of a new acquisition system
based on ASIC, FPGA, etc technologies.
• Applications with thicker scintillation crystals (1 cm) may become possible, without compromising
its good performance, thanks to the more accurate measurement of the DOI. (Tests are in
progress).
?
M. Ritzert et al., Heidelberg University
Summary & Outlook
• We have developed a γ-camera with spatial resolution, linearity and field of view substantially
improved with respect to similar existing devices
• Our system uses conventional NIM and VME electronics, which makes it not optimal for medical
applications. However, this problem could be overcomed by means of a new acquisition system
based on ASIC, FPGA, etc technologies.
• Applications with thicker scintillation crystals (1 cm) may become possible, without compromising
its good performance, thanks to the more accurate measurement of the DOI. (Tests are in
progress).
APV25 chip (from CERN CMS experiment)
128-channel
analogue
pipeline chip
?
M.J. French et al., NIMA 466 (2001) 359-365
Thank you for your attention!
Summary & Outlook
• We have developed a γ-camera with spatial resolution, linearity and field of view substantially
improved with respect to similar existing devices
• Our system uses conventional NIM and VME electronics, which makes it not optimal for medical
applications. However, this problem could be overcomed by means of a new acquisition system
based on ASIC, FPGA, etc technologies.
• Applications with thicker scintillation crystals (1 cm) may become possible, without compromising
its good performance, thanks to the more accurate measurement of the DOI. (Tests are in
progress).
6 cm
Germanium detector
Energy resolution
conduction band
electrons
p
0.7 eV
n
3 eV
holes
valance band
signal
+ HV
Number of e-h pairs for 1 MeV, N = 106 / 3 = 3 ×105
Energy resolution = N N = 0.0018 → 1.8 keV × E γ
Nuevo método experimental para la caracterización de
detectores de HPGe
Método convencional
BGO
• Duración aprox. 3 meses
z
y
x
Nuevo método experimental para la caracterización de
detectores de HPGe
Nuevo principio
a)
BGO
a)
z
F. Crespi, et al. NIMA (2008)
Nuevo método experimental para la caracterización de
detectores de HPGe
Nuevo principio
b)
a)
BGO
Criterio
χ2(a,b)
a)
z
b)
Punto geométrico de intersección: x,y,z
Pulso común a ambos
grupos de datos
F. Crespi, et al. NIMA (2008)