Semi-insulating GaAs detectors with HDPE layer for detection of fast neutrons from D–T nuclear reaction

Andrea Sagatova,Vladimir Necas,Bohumir Zatko,Carlos Granja,Marius Pavlovic,Katarina Sedlackova,Marko Fulop,Michael Solar

doi:10.1142/s2010194516602337

Abstract

Bulk semi-insulating (SI) GaAs detectors optimized for fast-neutron detection were examined using mono-energetic neutrons. The detectors have an active area of 7.36 mm2 defined by a multi-pixel structure of a AuZn Schottky contact allowing a relatively high breakdown voltage (300 V) sufficient for full depletion of the detector structure. The Schottky contact is covered by a HDPE (high density polyethylene) conversion layer, where neutrons transfer their kinetic energy to hydrogen atoms through elastic nuclear collisions. The detectors were exposed to mono-energetic neutrons generated by a deuterium (D)–tritium (T) nuclear reaction at a Van de Graaff accelerator. Neutrons reached a kinetic energy of 16.8 MeV when deuterons were accelerated by 1 MV potential. The influence of the HDPE layer thickness on the detection efficiency of the fast neutrons was studied. The thickness of the conversion layer varied from 50 [Formula: see text]m to 1300 [Formula: see text]m. The increase of the HDPE layer thickness led to a higher detection efficiency due to higher conversion efficiency of the HDPE layer. The effect of the active detector thickness modified by the detector reverse bias voltage on the detection efficiency was also evaluated. By increasing the detector reverse voltage, the detector active volume expands to the depth and also to the sides, slightly increasing the neutron detection efficiency.

Highlights

Detectors of fast neutrons find applications in many areas such as nuclear medicine, nuclear power engineering, high-energy physics, materials science, and astrophysics
Two parameters were observed in our experiments: the neutron conversion layer thickness and the reverse voltage applied to the SI GaAs detector
The conversion efficiency of the high density polyethylene (HDPE) conversion layer is determined by two phenomena

Summary

Introduction

Detectors of fast neutrons find applications in many areas such as nuclear medicine, nuclear power engineering, high-energy physics, materials science, and astrophysics. We have optimized our bulk semi-insulating (SI) GaAs detectors for fast-neutron detection by a multi-pixel structure of a Schottky contact.[7] Neutrons are converted by (n,p) elastic nuclear collisions in an HDPE layer covering the Schottky contact. The SI GaAs detector detects the recoil protons,[5] and the HDPE layer is directly sensitive to the fast neutrons.[10,11] As the protons are slowed down in the detector volume, electron‐hole pairs are created. The first steeply decreasing part of the spectra (up to channel 30) corresponds to the preamplifier and detector noise, and the second part (channels 30 up to 300) represents the neutron detection

Results and Discussion

Active detector thickness effect

Conclusions