The influence of matrix effect on neutron-neutron angular correlation and energy-angle correlation of special nuclear material

The fission neutron will show a certain angular correlation due to the momentum enhancement of fission fragments. Neutron-neutron angular correlation is related to the intrinsic characteristics of the nucleus and can be applied to the characterization of nuclear materials. Currently, the mechanism related to the influence of matrix effects on neutron-neutron angular correlation of nuclear materials is not clear, which leads to the deviation. In this paper, a liquid scintillation detection system was built by Geant4 to investigate the matrix effects of nuclear materials. It is found that the change of neutron-neutron angular correlation mainly comes from the effect of induced fission and neutron scattering. Meanwhile, this paper also investigates the neutron anisotropy in different energy regions and the change of neutron-neutron angular correlation, and obtains the distribution of neutron-neutron energy-angle correlation, which further reveals the nature of neutron energy angular correlation. It is shown that neutron-neutron angular correlation is strongly affected by the matrix effect of nuclear materials and cannot be used to characterize the properties of nuclear materials. The neutron-neutron energy-angle correlation achieves feature enhancement by coupling the angle and energy information of fission neutrons, and has great potential in the radionuclide identification. The findings of this study on the matrix effect and the proposed energy-angle correlation analysis have significant potential for application in nuclear security and safeguards.