A single detector spectrometric portal monitoring concept solving the problems of 'innocent alarms'

In order to overcome the problems of 'innocent alarms' due to naturally occurring radioactive material (NORM) in vehicle monitoring and to medical isotopes in pedestrian monitoring, a new technology has been developed in the last few years, based on gamma spectrometry. The US Domestic Nuclear Detection Office (DNDO) has started a new approach to dynamic primary screening of vehicles, namely, advanced spectrometric portals (ASPs) based on multiple NaI scintillation or HPGe detectors. Complex and expensive instruments with up to 14 large volume NaI or HPGe detectors have been built and are presently being tested by DNDO. Up to now, it seems that these ASPs cannot meet the goal of detecting HEU masked by NORM 95% of the time. Even if this could be achieved, the approach is extremely expensive. The proposed new concept is based on a single detector spectrometric portal monitor (SRPM) with one large NaI crystal for dynamic primary screening of pedestrians, luggage, parcels, mail, etc., with immediate identification of innocent alarms. In addition, the SRPM can be used for secondary screening of vehicles in static mode after an alarm is triggered by a conventional plastic scintillator radiation portal monitor. After identification by the SRPM, the radiation source can be quickly localized with a highly sensitive gamma or neutron search detector, faster and easier as compared to a conventional radioisotope identifier device. One SRPM can serve several primary vehicle lanes for secondary inspection. This makes it even more economic. The paper describes test results obtained with a new SRPM, the SPIR IDENT, developed by SynOdys, France. Extensive testing, partly in cooperation with the IAEA, indicates that this instrument can meet the requirements of the IAEA, the International Electrotechnical Commission (IEC) and the American National Standards Institute (ANSI) for dynamic pedestrian monitoring as well as the IEC and ANSI requirements for static vehicle monitoring in secondary screening within a few minutes. (author)