Precise implementation of the Goldstein current model for self-powered neutron detectors and comparative analysis of its approximate approaches

Abstract

Self-powered neutron detectors (SPND) have been commonly used in reactors to monitor neutron flux density based on their response current. The Goldstein model is a typical Monte-Carlo model used to calculate steady-state SPND current. Compared with other models, the conductive current at steady state due to the space charge effect was included and calculated in the Goldstein model, and some approximate approaches were introduced due to the limitations of the used Monte Carlo software or for the sake of fast calculations. Hence, considering that Geant4 can trace the trajectories of charged particles in electric field, a more precise implementation of the Goldstein current model—accounting for charge transport under the actual electric field—has been carried out based on Geant4 in this work. In the precise implementation, the response current is accurately calculated by simulating the electron transported under the actual electric field, and actual charge density distribution is also obtained. Compared with the experimental result, the relative deviation of the response current calculated by the precise implementation is 8.99 %, while for the three approximation approaches, the deviations are 9.49 %, 10.15 %, and 11.39 %, respectively. In addition, six parameters affecting the detector response were scanned within the conventional variation range for comparative analysis of the three approximate approaches. The results show that the approximate approach #1 always gives the most precise result and that considering the practical application situations the insulator resistivity is the most key parameter affecting the space charge effect. It is worth mentioning that when the peak electric potential in insulator is a few kV or even less, the approximate approaches are acceptable, especially for the situation of quick calculation.