Simulation Study On Neutron Multiplicity Measurement Analysis Method

Nuclear material is the core of nuclear weapons, the quality measurement of nuclear material, has been a central issue in the field of verification. With the development of time, nuclear materials and technology has been successfully transition from military to civilian, it also means increasing the chance of nuclear proliferation. Therefore, the development of non-destructive assay technique for materials is meaningful. Neutron multiplicity measurement analysis is a emerging non-destructive assay technique to measure the mass of nuclear material, which is based on the coincidence measurement.This paper mainly describes the measurement principle of neutron multiplicity measurement analysis, comparing the theoretical formula of both(active and passive) neutron multiplicity measurement and researching the neutron multiplicity counter and multiplicity measuring electronics.This thesis discusses that 3He tubes' parameter how to influence the detection efficiency of detector. Using MCNPX program builds a physical model of the Active Well Neutron Coincidence Counter(AWCC), and we will get different detection efficiency by changing the parameters(length, number, space) of 3He tubes. According to the data obtained, we get a optimized layout for 3He tubes:the length of tubes is 18 cm, the space between tubes is 4 cm and the number of tubes of each lap is 12. So ultimately get the highest detection efficiency of AWCC is 50.7%.Through simulation method, it is the first time to use a Portable Neutron Coincidence Counter(PNCC) for active neutron multiplicity measurement. Through the simulation PNCC by MCNPX program to measure the uranium samples, getting the multiplicity distribution of fission neutron and pulse time train of neutron detected, proved that it is feasible to use a Portable Neutron Coincidence Counter(PNCC) for active neutron multiplicity measurement. Then, according to the principle of neutron pulse train generation, the time interval between two fission is added to pulse time train of neutron detected, these time intervals generated by MATLAB conforms to Poisson distribution, ultimately get the neutron pulse train based on the same starting point. This attempt provide valuable experience for developing portable and flexible neutron multiplicity counter in the future.