Weight and counting efficiency optimization in a moderated neutron detection system

This paper describes a technique in which a polyethylene moderated neutron detector was designed in order to have the optimum combination of maximum counting efficiency and minimum weight. Such a detector would be of use in arms control, counter proliferation or treaty verification applications, in which measurement time and system portability are important considerations. In such applications, the neutron source may be a spontaneous fissioning isotope such as Pu240. After consideration of many different neutron detection schemes, the paper concludes that the best detection scheme for this problem would be a system which utilizes He3 gas filled detectors surrounded by a moderator material. oderator weight efficiency” concept was developed as the basis for comparisons of different moderators and geometries. The MCNP neutron transport code was then used to evaluate moderator efficiencies for these different systems. The moderators considered by the paper included light water, heavy water, graphite, and polyethylene. The moderator geometries considered were a variety of shapes between (and including) planar and cylindrical. The paper describes an optimized system, which was found to have a combination of maximum performance and minimum moderator and system weight. timized detector was then fabricated and experimentally tested against another system, one which is currently employed in the INF treaty between Russia and the United States. Results are presented which show that the “optimized” system has higher counts per unit moderator (and system) weight than the INF comparison system.