In Situ Pu isotopic measurements using electromechanically cooled HPGe detectors at PFPF Page: 4 of 11
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The unique feature of this assay system is that the high purity Ge (HPGe) detectors used for
the gamma-ray measurement use electromechanical cooling instead of liquid nitrogen. The
remainder of this report will discuss the high resolution gamma-ray spectroscopy (HRGS)
equipment, the measurement performance with the mechanical cooling system, and the latest
commercial equipment developments for HRGS measurements using mechanical cooling.
Each HRGS system consists of:
" a Canberra HPGe coaxial detector (model GC25175) with 25% relative efficiency
" a Canberra Cryoelectric II electrically refrigerated cryostat
" 25 ft gas lines between the HPGe detector and the cryostat
" a Perkin Elmer (ORTEC) DSPEC-Plus digital spectrometer
" a tungsten collimator with additional cadmium filters
* a desktop computer with a Windows 95/98/NT operating system
* Perkin Elmer MAESTRO software to operate the DSPEC and collect the gamma-ray
* FRAM and MGA. isotopic analysis software
Figures 1 through 3 are photographs of the HPGe detector components. Figure 1 shows the
detector attached to the support plate that provides rigid support for both the detector and the front
and rear tungsten shields. The detector/shield support plate mounts to the lifter supplied by the
facility. The measurement location is approximately 3 meters above the floor, so a mechanical
lifting device is needed to support the weight of the detector and collimator. The purpose of the rear
shield is to block gamma rays coming from other material located in the room. Measurements made
at the facility during the calibration exercise show that room background is not a problem, so the
rear shield does not need to be used, but it is available if the need occurs.
Fig. 1. Photograph of
the HPGe detector
mounted on the support
plate with the tungsten
shield. A rear tungsten
shield is also included
to shield the detector
from material located
c s directly behind it.
Figure 2 shows the LEDs that are on the preamplifier portion of the HPGe detector-these are
visible on the opposite side of the detector shown in Fig. 1. A rectangular hole was cut in the
tungsten collimator so that these lights are visible. The LEDs operate when the detector is
connected to the DSPEC Plus spectrometer with the main power on the HV turned off This
configuration supplies power to the preamplifier for checking the status of the LEDs prior to turning
on the HV.
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Wenz, T. R. (Tracy R.); Menlove, Howard O.; Maruyama, H. (Hajime); Fujiwara, S. (Shigeo) & Takahashi, S. (Saburo). In Situ Pu isotopic measurements using electromechanically cooled HPGe detectors at PFPF, article, January 1, 2001; United States. (https://digital.library.unt.edu/ark:/67531/metadc933990/m1/4/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.