Efficiency limitation of thin film coated planar semiconductor thermal neutron detector

Abstract

Semiconductor thermal neutron detectors are increasingly been used in in-core thermal neutron flux measurements in nuclear reactors. One limitation of these detectors is that they suffer from low detection efficiency. In this work, the maximum efficiency of a planar structure thermal neutron detector was determined using two widely used computer codes: Geant4 and MCNP6. Diamond and SiC are used as based materials in this work because of their large electron-hole pair production efficiency which generally translates to high detection efficiency. The electron-hole pair production efficiency is the fraction of energy that goes into electron-hole pair creation and depends on the band-gap energy and the W-values. These two materials are also not susceptible to radiation damage which makes them suitable for high radiation environments such as nuclear reactors. Thermal neutron detection is achieved using 10B and 6LiF conversion layers coated on the surface of the detector. The maximum efficiency for 10B conversion layer was achieved at a thickness of 2 μm. The efficiency at this thickness is 5.57 ± 0.09% and 5.49±0.09% for diamond and silicon carbide, respectively. When 6LiF was used as a thermal neutron conversion layer, the maximum thickness of the conversion layer was determined to occur at 17 μm. The efficiency at this thickness is 5.47 ±0.06% and 5.38±0.06% for diamond and SiC, respectively.