Boric acid as converter material for semiconductor neutron detector- A GEANT4 simulation study

摘要

Monte Carlo based GEANT4 simulations have been carried out to estimate the efficiency (eta) of thermal neutron detection with boric acid (H3BO3) as a converter material. Different geometries of detector configurations - planar stack, sphere, cylinder and cuboid were considered and their efficiency were computed for relevant geometric parameters along with different B-10 enrichment (B-E) levels content in boric acid, with Low Level Discriminator (LLD) value fixed at 300 keV. The planar stack configuration detector was designed by replicating two dimensional detector units (DUs) - each consisting of boric acid as a converter material and Silicon (Si) as a detector material - in the third dimension. The simulation carried out for varied layer thicknesses (0.25 mu m to 10 mu m) of boric acid showed that efficiency (eta) increased with increasing thickness, reached a maximum at a critical thickness (t(sc)) and thereafter found to decrease. Typically, at a critical thickness of similar to 3.5 mu m, the eta for 100% B E content in boric acid was found to be 15.96% for 30 DUs. For the case of sphere, cylinder and cuboid of boric acid embedded in Si, the simulations were performed for diameter and width both varying from 0.5 mu m to 9.5 mu m in steps of 0.5 mu m. In particular for cylinder and cuboid geometries, the depth was also varied from 25 mu m to 275 mu m with a step size of 25 mu m. In all these configurations eta was found to increase initially and was maximum at a critical diameter and width of similar to 8-9 mu m, and thereafter it was found to reduce. Apart from the simulated eta estimation, histogram plots depicting the energy deposited in Si detector region by the generated charged particles (Li-7 = 0.839 MeV and alpha = 1.47 MeV) upon thermal neutron interaction in boric acid have also been studied for various geometrical parameters such as thickness, diameter and width of detector.