An Analytical Method for Evaluating the Evolution of Space Charge Effect in Self-Powered Neutron Detectors

The space charge effect in self-powered neutron detector (SPND) insulators, as one of the key factors affecting detector performance, has always been a focus of research. Previous studies have provided iterative simulation algorithms; however, these algorithms are time-consuming and inefficient and do not directly explain how the detector parameters and neutron flux affect the space electric field and its evolution. Therefore, for the first time, we propose an analytical method to calculate the space charge effect. This method provides an analytical expression for the evolution of the space charge distribution, significantly improving computational efficiency. The analytical expression reveals that the space charge distribution is proportional to the neutron flux density, bulk resistivity, and dielectric constant of the insulator, which confirms the results from the previous numerical studies. Moreover, this work presents a method for calculating the time constant of the space charge evolution for the first time. Based on this time constant, the electric field equilibrium time can be predicted, providing guidance for presetting the time step in iterative calculations. Comparisons between the analytical predictions and iterative calculations were conducted for both cobalt SPND (Co-SPND) and rhodium SPND (Rh-SPND). The results from the analytical model and from the iterative model are consistent, demonstrating the accuracy of this proposed analytical method.