Year
2006
Abstract
The ORTEC Detective is an HPGe (High-Purity Germanium)-based portable nuclide identifier designed to search for and identify radionuclides to support the fight against illicit trafficking of nuclear materials. The Detective contains an HPGe crystal approximately 50 mm in diameter by 30 mm thick, cooled by a miniature mechanical cooler that operates from either battery or line power. The system weighs 10.6 kg and is easily man-portable for measurements where conventional liquid nitrogen (LN2) cooling for the detector is not available. The Detective operates with a fixed, unadjustable gain of 0.3662 keV/ch spanning 3 MeV in 8192 channels. The large, fixed keV/ch value coupled with relatively poor HPGe crystal resolution (excellent resolution is not required for the Detective’s search-and-identify purpose and is not specified for the instrument) makes this a challenging system to use for high-resolution spectroscopy applications such as gamma-ray isotopic analysis. Nevertheless, we have been able to successfully use the FRAM (Fixed energy, Response function Analysis with Multiple efficiencies) gamma-ray isotopic analysis code to extract the isotopic composition of uranium and plutonium from Detective gamma-ray spectra. We will present data from 21 well-characterized plutonium and uranium samples, including 12 certified reference materials, measured with three different Detectives and one conventional LN2-cooled coaxial detector under the same measurement conditions. The Detective data are generally unbiased but exhibit poorer statistical precision and greater variability compared with the LN2-cooled coaxial detector.