Spatial Distribution Assay of Active Neutron Counting

Abstract In response to the nuclear material accounting and control system, uranium or plutonium mass and also the isotope abundance should be quantified comprehensively. Commonly, in nuclear safeguards and nuclear security field, active mode is most reasonable for nuclides with low spontaneous rates like uranium measuring for neutron accounting equipment. The spatial detection efficiency and the number of induced fission neutrons are researched in the paper by Monte Carlo simulation and laboratory experiments. A geometric model is built for Monte Carlo simulation to symbolize the measurement of neutrons. The data are assayed with the fission time randomly generated by matlab that conforms to the Poisson distribution to obtain the neutron pulse sequence. The multiplicity shift register (MSR) simulation program performs statistical analysis on the neutron pulse sequence to obtain the corresponding count rates. After that, U3O8 standard source was placed at more than 50 positions, and the comprehensive simulations were conducted. Spatial detection efficiency is practically consistent in the measurement cavity, which proves that the main influencing factors of the neutron measurement results are the spatial distribution of the induction source and the sample. The spatial distribution curves obtained in the fitting results can be used to correct the spatial effect of neutron measurement in the active mode of this device and provide a reference for the subsequent optimization of active neutron measurement equipment and the application of different measurement scenarios.