Characterization of Segmented HPGe Detectors Using Pulse Shape Comparison Methods
F.C.L. Crespi a,b, V. Vandone a,b, F. Camera a,b, S. Brambilla b, B. Million b, S. Riboldi a,b , O. Wieland b
a Physics Department, University of Milan, Via Celoria 16, 20133 Milano, Italy
b INFN Sezione di Milano, Via Celoria 16, 20133 Milano, Italy
A. Boston c, C. Unsworth c
c Department of Physics, University of Liverpool, Liverpool L69 3BX, UK
Large volume (240 cm3), Highly segmented HPGe detectors
Digital electronics to record and process signals from segment
Determination of the detector position response
Pulse Shape Analysis (PSA) to decompose recorded signals
Reconstruction of tracks evaluating permutations of Interaction Points (IPs)
g-ray Tracking Detectors
g
Reconstructed Gamma Energy Spectrum
Energy (keV)
Abstract
Pulse Shape Comparison Scan (PSCS) – Basic Idea -
AGATA Demonstrator
In many in-beam gamma spectroscopy experiments the detection of high- energy gamma rays in the range up to 10-20 MeV is of primary importance.
New generation high-resolution gamma-ray spectrometers like AGATA and GRETA are composed of position sensitive segmented HPGe detectors and provide a reconstruction of the gamma-ray tracks. The performance of AGATA detectors in this energy range has, however, never been studied in detail. A measurement of the response to 15.1 MeV gamma rays has therefore been performed using two HPGe triple clusters of the AGATA Demonstrator array, operating at LNL-INFN. This study represents a crucial test of the AGATA detectors for the measurement of high-energy gamma rays, in terms of detection efficiency, energy resolution, tracking and performance of the pulse shape analysis (PSA) algorithms.
The technique is based on a specific pulse shape comparison procedure (therefore we named it Pulse Shape Comparison Scan, PSCS).
The main difference between the PSCS and standard techniques is that PSCS does not require any ‘coincidence’ between events: this approach allows to enormously decrease the time duration of the measurements. In highly segmented HPGe detectors (e.g. AGATA), two different single-interaction gamma events give rise to clearly distinguishable signal shapes. To identify the gamma ray interaction point position 2 data sets are used: each one corresponding to a specific measurement characterized by a defined collimation of the gamma ray source. In fact, the only case in which a signal of one set is identical to a signal of the other is when the two signals originate at the position corresponding to the crossing point of the two lines defined by the source collimation.
Conclusions
Different sets of collimated data have been acquired with the Liverpool University Scanning system [1].
Front face and lateral single scan data have been used to test the Pulse Shape Comparison based Scan (PSCS) [2] and extract the signal basis for 4 detector segments (A1,A2,F1,F2). The obtained Signal Shapes are compared with those extracted with the standard Coincidence Scan and the calculated basis. Although some discrepancies are present the general trend of the shape variation with position is consistent in all the cases. From the results of these first tests the PSCS showed to be a valuable tool to extract the position response of HPGe segmented detectors.
[1]A. Boston, et al., Nucl. Inst. and Meth. B 261 (2007) 1098-1102
[2] F.C.L. Crespi, et al, Nucl. Instr. and Meth. A 593 (2008), p. 440.
Data Acquired with the Liverpool University Scanning System to Test the PSCS Method
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20 40 60 80
Amplitude (A.U.)
Time (10*ns) -40
-20 0 20 40 60 80 100 120 140 160
20 40 60 80
Amplitude (A.U.)
Time (10*ns) -20
0 20 40 60 80 100 120 140 160
20 40 60 80
Amplitude (A.U.)
Time (10*ns)
-20 0 20 40 60 80 100 120 140 160
20 40 60 80
Amplitude (A.U.)
Time (10*ns)
1
3 0
2
0 2
3
Coincidence Scan Data Front Face Singles Scan Data
120 3
880 (0.1*mm), 500 (0.1*mm), 50.5 (0.1*mm)
Pos X’ Pos Y’ Pos Z
Coincidence scan PSCS scan Calculated Basis
Pos X [0.1*mm]
PosY [0.1*mm]
-30 -10 10 30 50 70 90 110
0 60 120 180 240 300 360
1 2 3 4 5 6
TIME [10*ns]
AMPLITUDE [a.u.]
882 493 806 513
883 523 839 504
883 554 873 500
884 585 906 500
885 616 940 504
886 646 973 513
887 677
888 708
889 739
Pos Y [0.1*mm]
Pos X [0.1*mm]
Pos X [0.1*mm]
Pos Y [0.1*mm]
•Traces of 128 samples digitized at 100 MHz
• The trigger was generated through a CFD on
• the core with a threshold of
~300 keV
137Cs source collimated to 1mm swept across Front face of the detector
Step Lenght = 1 mm Step Duration = 60 s
X-start 48 mm, X-range 86 mm Y-start 39 mm, Y-range 86 mm
137Cs
Front Face Singles Scan
137Cs source collimated to 1mm swept across Side face of the detector
Step Length = 1 mm Step Duration = 30 s
X-start 3 mm, X-range 82 mm Y-start 38 mm, Y-range 95 mm
137Cs
137Cs source collimated to 1mm swept across Side face of the detector (Step Dur. = 150s)
(performed only for 2 detector rings)
Side Singles Scan Data
Higher Statistics Side Singles Scan Data
1 5 6 3 24
-30 -10 10 30 50 70 90 110
0 60 120 180 240 300 360
1 2 3 4 5 6
TIME [10*ns]
AMPLITUDE [a.u.]
-30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110
0 60 120 180 240 300 360
1 2 3 4 5 6
TIME [10*ns]
AMPLITUDE [a.u.]
-30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110
0 60 120 180 240 300 360
1 2 3 4 5 6
TIME [10*ns]
AMPLITUDE [a.u.]
-30 -10 10 30 50 70 90 110
0 60 120 180 240 300 360
1 2 3 4 5 6
TIME [10*ns]
AMPLITUDE [a.u.]
-30 -10 10 30 50 70 90 110
0 60 120 180 240 300 360
1 2 3 4 5 6
TIME [10*ns]
AMPLITUDE [a.u.]
A simple test has been performed to check the consistency of the data:
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20 40 60 80
Amplitude (A.U.)
Time (10*ns) -20
0 20 40 60 80 100 120 140 160
20 40 60 80
Amplitude (A.U.)
Time (10*ns)
-20 0 20 40 60 80 100 120 140 160
20 40 60 80
Amplitude (A.U.)
Time (10*ns) -20
0 20 40 60 80 100 120 140 160
20 40 60 80
Amplitude (A.U.)
Time (10*ns)
1
3 0
2
0 2
3
Coincidence Scan Data Front Face Singles Scan Data 890 (0.1*mm), 740 (0.1*mm), 50.5 (0.1*mm)
Pos X Pos Y Pos Z
TIME [10*ns] TIME [10*ns] TIME [10*ns]
-40 -20 0 20 40 60 80 100 120
0 60 120 180 240 300 360
TIME [10*ns]
AMPLITUDE [a.u.]
-40 -20 0 20 40 60 80 100 120
0 60 120 180 240 300 360
-40 -20 0 20 40 60 80 100 120
0 60 120 180 240 300 360
TIME [10*ns]
TIME [10*ns]
All Multiplicities Multiplicity > 0.3*Max_Mult Multiplicity > 0.5*Max_Mult
-40 -20 0 20 40 60 80 100 120
0 60 120 180 240 300 360
-40 -20 0 20 40 60 80 100 120
0 60 120 180 240 300 360
Selecting Shapes with an higher “Multiplicity”
value allows to obtain an improved result
PSCP has been used to extract the position response
of 4 detector segments:
A1,A2,F1,F2
*Pos Z = 4 mm (in all the cases)
Z(0.1*mm)
Y (0.1*mm)
X (0.1*mm) X’ (0.1*mm)
