Survivability of microstructure semiconductor neutron detectors (MSND) in a thermal neutron radiation environment

Abstract

The performance of five representative microstructured semiconductor neutron detectors (MSND) were investigated after exposure to varying magnitudes of thermal neutrons fluences ranging from 107 cm−2 to 1012 n cm−2. The devices have 95% enriched microparticulate 6LiF granules backfilled in microscopic trenches within a Si pvn diode. Neutron interactions in the 6Li causes the emission of reaction products which ionize the trenched Si diode depletion regions. The average intrinsic thermal-neutron detection efficiency (ϵtn) of the five devices before irradiation measured as 24.09% ± 0.35% with an operating leakage current below 11 nA at a −3 V reverse bias condition. The observed threshold of performance deterioration was approximately 1010 n cm−2, resulting in an spectral shift in the reaction product spectrum to lower energy channels and a general increase in leakage current. Although damage was observed beyond a thermal-neutron fluence of 1010 n cm−2, the devices remained operable. Beyond a thermal-neutron fluence of 1012 n cm−2, the devices experienced severe damage and demonstrated poor detector performance. At the highest thermal neutron fluences tested, near 1012 n cm−2, the average ϵtn of the five devices decreased to 4.42% ± 0.10% with an average operating leakage current of 300 nA at a −3 V reverse bias condition. Performance degradation was attributed to reaction-product damage in the MSND pvn diode structure.