MCNPX Monte Carlo simulations of particle transport in SiC semiconductor detectors of fast neutrons

Abstract

The aim of this paper was to investigate particletransport properties of a fast neutron detector based on silicon carbide.MCNPX (Monte Carlo N-Particle eXtended) code was used in our study becauseit allows seamless particle transport, thus not only interacting neutronscan be inspected but also secondary particles can be banked for subsequenttransport. Modelling of the fast-neutron response of a SiC detector wascarried out for fast neutrons produced by 239Pu-Be source with the meanenergy of about 4.3 MeV. Using the MCNPX code, the following quantities havebeen calculated: secondary particle flux densities, reaction rates ofelastic/inelastic scattering and other nuclear reactions, distribution ofresidual ions, deposited energy and energy distribution of pulses. Thevalues of reaction rates calculated for different types of reactions andresulting energy deposition values showed that the incident neutronstransfer part of the carried energy predominantly via elastic scattering onsilicon and carbon atoms. Other fast-neutron induced reactions includeinelastic scattering and nuclear reactions followed by production of α-particles and protons. Silicon and carbon recoil atoms, α-particles and protons are charged particles which contribute to thedetector response. It was demonstrated that although the bare SiC materialcan register fast neutrons directly, its detection efficiency can beenlarged if it is covered by an appropriate conversion layer. Comparison ofthe simulation results with experimental data was successfully accomplished.