GBS Elektronik MCA166-USB Dependence of HPGe Detector resolution on shaping time User Manual
GBS Elektronik Equipment
Application Note
Dependence of HPGe Detector resolution on shaping time
10.1.2001
Jörg Brutscher
GBS Elektronik GmbH
Problem:
A number of HPGe detectors are specified for shaping times >2µs wheras the standard version of the MCA166 allows
only shaping times of 1 and 2µs. Additionally, some larger detectors (>30% efficiency) demand voltages >3000V which
the MCA166 cannot deliver. The effects of operating HPGe detector below their specifications are investigated.
Experiment:
For this report, a MCA 166 was manufactured with a shaping time of 4 and 6 µs (optionally available). This unit was
compared in terms of resolution with a conventional unit with 1 and 2 µs.
The following detectors were used for report:
•
GL0310R - This is a Canberra planar detector (crystal 300mm², 10mm thick) specified for -2000V and a shaping
time of 2µs
•
GMX20190S - This is a Ortec coaxial detector (20% relative efficiency) specified for -3000V and a shaping time of
6 µs.
•
BG2020 - This is a larger Canberra planar detector (rel. efficiency 9%, crystal 2000mm², 20mm thick) specified for
4µs shaping time and +3000V.
•
GX3518 - Canberra coaxial detector, 35% rel. efficiency, specified for 4µs shaping time and +4000V (+3000V
applied)
•
EGPC25-185R - Silena coaxial detector, 25% rel. efficiency, specified for 6µs shaping time and +2000V
The peaks were adjusted always to the same channels, for each measurement P/Z was adjusted by the automatic option
of WinMCA.
Table: Measured resolution for different shaping times.
shaping time
122 keV
136 keV
1173 keV
1333 keV
GMX20190S
1
1
1.05
2.26
2.42
2
0.83
0.84
1.95
2.08
4
0.75
0.8
1.86
2.02
6
0.74
0.72
1.78
1.98
GL0310R
1GL0310
0.607
2
0.571
4
0.583
6
0.597
BG2020
1
0.701
0.706
2.207
2.361
2
0.59
0.622
1.602
1.727
4
0.587
0.62
1.595
1.679
6
0.579
0.603
1.541
1.647
GX3518
1
1.4
1.41
3.222
3.442
2
1.1
1.08
2.033
2.142
4
0.95
0.94
1.843
1.955
6
0.93
0.93
1.856
1.85
EGPC25-185
1
0.92
0.95
4.026
4.402
2
0.803
0.821
1.987
2.093
4
0.878
0.87
1.716
1.786
6
0.776
0.781
1.686
1.743