Evaluation of two rounds of testing of types of devices for monitoring radioactive sources in loaded vehicles

Tests of stationary devices for the detection of radioactive sources in moving trucks were performed by the Czech Metrological Institute – Inspectorate for Ionising Radiation, Prague in December 1996 and September 1997. The different systems were installed at a railway polygon. Each system contained two detection units placed symmetrically at the rail in a distance 2.3 m from the axes of each rail. The train comprising empty and scrap-filled trucks passed along the detection units at a speed of 5–30 km/h. The wide range of radioactive sources with 137Cs (activity ranging from 0.4 MBq to 5 GBq) were located at different positions in the truck. The purpose was to determine a detection limit under different conditions. Sources with 57Co, 60Co, 241Am were also used. The truck passed the polygon more than 1000 times. About 250 passes were free of source. All systems were also tested in a climatic chamber. The main parameters evaluated were the detection limit for an empty truck, detection limit for a truck filled with scrap (density 0.89 t/m3), percentage of false alarms and stability of response at different temperatures. The other parameters like energy dependence, position dependence, linearity and overload, detection response time, etc., were also evaluated. The tested systems showing a positive result will be used in the field of steel recycling, metallurgy and the supervision of illegal transport.