Performance of a Portable, Electromechanically-Cooled HPGe Detector for Site Characterization

High-resolution, germanium detectors (HPGe) have long been used for radionuclide characterization of nuclear sites, both buildings and large areas, for the purpose of cleaning up the site. Several systems consisting of a detector, mobile support, collimators and software for data collection and spectrum analysis have been made by national laboratories and commercial companies. The efficacy of these systems is well accepted. The use of HPGe detectors is complicated by the need for cryogenic cooling of the HPGe detector. The traditional method of cooling used liquid nitrogen and the handling of liquid nitrogen in field situations is always difficult. Laboratory type electromechanical coolers have been used for years, but only recently have developments in low-power electromechanical cooling for HPGe detectors made possible the construction of low weight, portable HPGe spectrometers with sufficient efficiency to perform the needed measurements in reasonable count times. The use of a battery-operated cooler simplifies the field operation by eliminating the need for transportation and storage of liquid nitrogen. The 12 volt DC power needed can be easily provided by AC adapter, additional battery packs, or automobile power.