Performance study of thin epitaxial silicon PIN detectors for thermal neutron measurements with reduced γ sensitivity

A novel approach of using thin epitaxial silicon PIN detectors for thermal neutron measurements with reduced γ sensitivity has been presented. Monte Carlo simulations showed that there is a significant reduction in the gamma sensitivity for thin detectors with the thickness of 10-25μm compared to a detector of thickness of 300μm. Epitaxial PIN silicon detectors with the thickness of 10μm, 15μm and 25μm were fabricated using a custom process. The detectors exhibited low leakage currents of a few nano-amperes. The gamma sensitivity of the detectors was experimentally studied using a 33 μCi, 662 keV, 137Cs source. Considering the count rates, compared to a 300μm thick detector, the gamma sensitivity of the 10μm, 15μm and 25μm thick detectors was reduced by factors of 1874, 187 and 18 respectively. The detector performance for thermal neutrons was subsequently investigated with a thermal neutron beam using an enriched 10B film as a neutron converter layer. The thermal neutron spectra for all three detectors exhibited three distinct regions corresponding to the 4He and 7Li charge products released in the 10B-n reaction. With a 10B converter, the count rates were 1466 cps, 3170 cps and 2980 cps for the detectors of thicknesses of 10μm, 25μm and 300μm respectively. The thermal neutron response of thin detectors with 10μm and 25μm thickness showed significant reduction in the gamma sensitivity compared to that observed for the 300μm thick detector. Considering the total count rate obtained for thermal neutrons with a 10B converter film, the count rate without the converter layer were about 4%, 7% and 36% for detectors with thicknesses of 10μm, 25μm and 300μm respectively. The detector with 10μm thickness showed negligible gamma sensitivity of 4 cps, but higher electronic noise and reduced pulse heights. The detector with 25μm thickness demonstrated the best performance with respect to electronic noise, thermal neutron response and gamma sensitivity.