Detection of Nuclear Material During Fast Road Transport

For the search and detection of nuclear material during road transport we equipped a conventional car with a radiation measurement system. For the detection of neutron radiation we use six high efficient neutron slab counters at each side of the car with appropriate electronics. The pulses of the modules on each side are analyzed separately. Additionally, the car is equipped with a natural background reduction (NBR) gamma measuring system consisting of a large plastic scintillator with accessory electronics and a special evaluation procedure to distinguish between natural and artificial radiation. The neutron intensity can be displayed on a handheld PC in the front of the car together with the results of the gamma measurement and GPS position information. In case of a covered search the data can be stored in a non-volatile memory. The system is assembled in modules so that it can easily be fixed in many different types of vehicles. We have investigated in procedures of detecting nuclear material being transported on a road by measuring neutron and gamma radiation in that car. Therefore, we performed measurements at various speeds and various distances between the transporting vehicle and the measurement car. Especially neutron detection is very effective as shielding is complicated and voluminous. A mass of 1.4 kg of weapon-grade plutonium can be detected in a distance of 10 m during the measuring interval of 2 seconds. This quantity corresponds to a mass of 260 g of reactor plutonium. By passing the suspect vehicle on a highway with separate lanes even a smaller amount of plutonium can be detected. Results of our measurements and the limits of the system are reported. This car is well suited to discover illicit trafficking of nuclear material on roads and consequently may help to prohibit nuclear proliferation.