Year
2003
Abstract
The detection and identification of chemical and nuclear materials for safeguards and interdiction purposes often depend on the analysis of the complex gamma ray spectra from the material, either directly or induced by neutron interrogation. The gamma-ray detector should have sufficient stopping power for the high energy gamma rays and sufficient resolution to separate the individual gamma rays in the analysis. To be of practical use for the portable applications, the detector element must be of a size adequate to collect sufficient data in reasonable measurement times. Only HPGe detectors can combine adequate size and stopping power with high resolution, but they must be cryogenically cooled to operate. Many electro-mechanically cooled detectors have been developed to overcome this limitation for use in fixed installations. These coolers have typically required significant electrical power and many are heavy. Commonly, such coolers may not be moved while operation or even relocated without extensive time to recover from the movement. The mechanical actions of the coolers can cause degradation of the resolution. Several recent advances have been made in refrigerator technology to overcome the power, transportation and vibration problems. This has enable several different low-power coolers to be developed for HPGe detectors. In this work, we investigate the absolute efficiency and resolution over a wide energy range for a HPGe detector designed for use in field identification of illicit materials. Results will be presented for efficiency from 60 keV to above 1.5 MeV in several common geometries, as well as resolution over the same energy range and incident geometries.