The safety of a landmine detection system using graphite and polyethylene moderator

Background: Several landmine detection methods, based on nuclear techniques, have been suggested up to now. Neutron-induced gamma emission, neutron and gamma attenuation, and fast neutron backscattering are the nuclear methods used for landmine detection. In this paper an optimized (safe and effective) moderating structure using an 241 Am-Be neutron source for detecting landmines has been investigated by experiment and MCNP simulation. Materials and Methods: The experimental set up was composed of a lead (Pb) cylindrical shell enclosing the neutron source, embedded in a fixed size high-density polyethylene (HDPe) cylinder with the variable thickness of the upper and lower moderator/reflector. Some experimental groups were used to measure several moderator configurations' responses by replacing a thermal neutron detector with the mine and counting the neutron capture events. Results: the total experimental results led to the introduction of optimum moderator geometry for landmine detection. A safe landmine detection system was obtained which enabled the operator to use it for 950 h/year, regarding the dose limit recommended by ICRP. Conclusion: The novel method for optimization applied in this work is more applicable than the usual approach that is based on measuring the prompt gamma rays emitted by the landmine. Results showed that the method can be optimized in short time, without the usual difficulties of the other methods. Iran. J. Radiat. Res., 2007; 5 (3): 137-142