Boron carbide based solid state neutron detectors: the effects of bias and time constant on detection efficiency

Abstract

Neutron detection in thick boron carbide(BC)/n-type Si heterojunction diodes shows a threefold increase in efficiency with applied bias and longer time constants. The improved efficiencies resulting from long time constants have been conclusively linked to the much longer charge collection times in the BC layer. Neutron detection signals from both the p-type BC layer and the n-type Si side of the heterojunction diode are observed, with comparable efficiencies. Collectively, these provide strong evidence that the semiconducting BC layer plays an active role in neutron detection, both in neutron capture and in charge generation and collection.

Novel n-type Mg2B14 on silicon diode: Demonstration of a thermal solid state neutron detector

“…As charge mobility is limited by band structure, Mg 2 B 14 as an n-type semiconductor should have higher charge mobility than B 4 C, considering bandstructure calculations from related materials [7,14]. We note the estimated efficiency of 0.53% for a B 4 C/Si diode (Table 1) is in good agreement with the experimental thermal efficiency reported by Hong et al [3] for an 1 mm boron carbide film deposited on n-Si, taking into account that in practice the detection efficiency is also dependent on the charge carrier production and collection, and as stated earlier for Mg 2 B 14 /Si the data is consistent with what is experimentally reported here. The efficiency of another p-type boride B 12 As 2 previously demonstrated on n-SiC substrates [2] is somewhat lower for the same geometry (Table 1).…”

“…In case of measurements with Cf-252 and liquid nitrogen cooling, the detector was placed in a shielded box and connected to the A250 preamplifier box by a short BNC cable, as the preamplifier can be used only down to À 50 1C. The A250 preamplifier output was connected to an Ortec spectroscopy amplifier Model 570, with the gain set to 50 and the shaping time set to 10 ms, as longer rise times are expected for boride semiconductors [3] compared to Si detectors with typical rise times of 20 ns. The pulse counting was recorded using an Ortec Easy-MCA 2 k digital multi channel analyzer and MAES-TRO32 software.…”

“…Among the elements in the periodic table that have large thermal neutron cross-section, boron generates easily detectable high energy ions ( 10 B(n,a) 7 Li reaction) and also forms a class of boron-rich radiation hard semiconductors. Several ptype boride semiconductors as B 12 As 2 [2], BC [3,4] and BP [5] have been explored for solid state neutron detector devices, in which the neutron converting element is present in the diode active charge collection volume (depletion region). These detectors benefit from higher attainable efficiencies, compared to the more limited efficiency of the boron covered semiconductor detectors, suffering from self-absorption losses in the converting layer [6].…”

Fabrication and characterization of silicon based thermal neutron detector with hot wire chemical vapor deposited boron carbide converter

“…The research and development effort in this area has been mainly focused to develop substitutes for conventional detectors such as 3 He or BF 3 detectors, with improvements in terms of device design and fabrication technology, cost, size, operating voltage/power and adaptability to different applications. Such solid state detectors have been realized by using a suitable converter layer along with a semiconductor detector [1][2][3][4][5][6] or by forming a converter layer as an integral part of the semiconductor device [7,8]. In the former case, the charged particle due to interaction of neutrons with the converter layer is detected by the semiconductor detector, while in the latter case, the charged particle is released by the interaction of neutrons in the device itself and is subsequently detected.…”

Nevada National Security Site Site-Directed Research and Development FY 2014 Annual Report

“…Indirect conversion device geometries place a thin film of neutronsensitive material within range of, but external to, an adjacent space-charge layer (LiCausi 2008, Caruso 2010, Melton 2011, Dahal 2012, Murphy 2012. In contrast, direct conversion heterostructures contain a neutron-sensitive material that can also be the space-charge layer (Robertson 2002;Caruso 2006Caruso , 2010Hong 2010). As a result, direct conversion is a straightforward method that has high total efficiencies.…”