Comparison of Several Detector Technologies for Measurement of Special Nuclear Materialsi

Gamma spectral analysis of measurements made on Special Nuclear Materials (SNM) provides identification and sometimes quantification of the SNM present. Different radiation detection technologies have been used for measurement of SNM. Selection of one of these for a particular application depends on the information that can be obtained using that detector and on the support needed to use the detection technology, especially if it is to be applied at sites where limited support is available. In some cases, detector selection may be determined by a need to limit the information available from measurements due to international treaty requirements. There are many studies of system capabilities in SNM measurement. Most of these used either scintillator or high-resolution (HPGe) detectors embedded in a unique electronics and software combination. Their respective developers claimed good results for their instrument. Unfortunately, the ‘packaging’ often obscured the question of what can be obtained from various detector technologies. While instrumentation and analysis is important, a study comparing only detector characteristics would serve as a starting point for development of systems for SMN measurement. Our detector study consisted of measurements on shielded and unshielded high-enriched uranium and Plutonium sources using detectors: NaI(Tl), Cadmium Zinc Telluride (CZT), Mercuric Iodide (HgI2), and two HPGe detectors, one with liquid nitrogen cooling and one with electromechanical cooling. Measurements were made simultaneously using all detectors. As expected, all detectors are suitable for SNM measurements in cases where one radionuclide, such as 235U, is the dominant constituent, but only the high-resolution detectors are suitable for isotopic composition determinations using ‘standard’ spectroscopic analysis. Room temperature semiconductor detectors (CZT, HgI2) can provide limited isotopic information. Development of improved analysis algorithms for room-temperature semiconductor detectors would be desirable because of their attractive characteristics: small sizes and minimal support requirements.