Year
1983
Abstract
Several types of radiation monitors, designed to search motor vehicles for special nuclear materials at area exit gates, were constructed and evaluated at the Los Alamos National Laboratory. These monitors consist of stationary radiation detection equipment or portable, hand-held instruments. The stationary monitors have either a detector portal through which vehicles pass or an underground detector array to measure radiation intensity from below a parked vehicle. Portal monitors straddle a vehicle path where they monitor vehicles in motion (at an ideal speed of 8 km/h) as they approach the exit gate, whereas the underground detector array is located in the roadbed at an exit station where vehicles stop for inspection. Roadbed monitors require a monitoring period of about one minute; hand-held monitors require several minutes. The sensitivity of the monitors depends on the size of the vehicle being monitored, the position and type of the nuclear material inside the vehicle, and the type and position of the radiation detectors. For small vehicles, adequate sensitivity can be obtained with any of the monitors. For slow moving vehicles up to 3.4 m high, the vehicle portal offers low-cost performance. The best performance, however, at a higher installation cost, is offered by the roadbed monitor supplemented with overhead detectors.