Monte Carlo simulations of correlation between anisotropic emission characteristics of prompt fission neutrons and sample multiplication

In the present study, the correlation between prompt neutron angular distributions and sample multiplication for three spontaneously fissionable nuclides (²⁵²Cf, ²⁴⁴Cm, and ²⁴⁰Pu) was quantitatively determined by Monte Carlo simulations with MCNP6.2 and Geant4.10. To this end, various parameters (i.e., point, area, gradient, and net-area-based parameters) were investigated to analyze the asymmetry of the angular distribution. It was confirmed that the asymmetry decreases as leakage multiplication increases, and that the extent of this variation depends on the given nuclear isotopes. After comparing the sensitivity of the asymmetry values to leakage multiplication, the net-area-based parameter was determined to be the optimal asymmetry parameter. Finally, fitting equations were determined in order to determine, by regression analysis, leakage multiplication as a function of the asymmetry parameter for each isotope of interest. The results presented here could contribute to the development of a fast-neutron-based coincidence counting technique for nuclear material accountancy in safeguards applications.