Nine element Si-based pillar structured thermal neutron detector

Abstract

Solid state thermal neutron detectors are desirable for replacing the current 3 He based technology, which has some limitations arising from stability, sensitivity to microphonics and the recent shortage of 3 He. Our approach to designing such solid state detectors is based on the combined use of high aspect ratio silicon PIN pillars surrounded by 10 B, the neutron converter material. To date, our highest measured detection efficiency is 20%. An efficiency of greater than 50% is expected while maintaining high gamma rejection, low power operation and fast timing for multiplicity counting for our engineered device architecture. The design of our device structure, progress towards a nine channel system and detector scaling challenges are presented.

High-efficiency microstructured semiconductor neutron detectors for direct 3He replacement

“…Semiconductor with a thin-film coating of neutron reactive material deposited on a planar rectifying diode have been investigated for the past few decades as a potential neutron detector technology while maintaining high gamma-ray rejection characteristics [1][2][3]. MSNDs were developed as a means of increasing the relatively low efficiency of the planar thin-film-coated devices (typicallyo4-5% intrinsic) up to their theoretical maximums above 40% intrinsic detection efficiency for single 0.5-mm thick devices [4][5][6][7][8][9][10][11][12][13][14][15][16] while maintaining gamma-ray rejection ratios (GRR) of 10 À 6 or better [12]. The increase in intrinsic neutron detection efficiency stems from the two primary benefits of perforating a semiconductor diode; increased neutron absorption and increased probability of interaction of the charged neutron reaction products in the semiconductor diode.…”

Nevada National Security Site-Directed Research and Development FY 2011 Annual Report

“…Also, their predictions are not directly comparable to others since they assume a 4π neutron source rather than a surface normal source. The published performance of the LLNL detector is ~20%, within the range of their predictions (Nikolić 2010). …”

“…In the past, semiconductor neutron detectors based on a planar diode configuration with a thin-film coating of a converter material (such as enriched boron [ 10 B], lithium [ 6 Li], or gadolinium [Gd]) were used. More recently silicon (Si) diode devices etched with perforated microstructures that are filled with converter material have been studied and found to be more efficient than the simple planar diode configurations (Conway 2009, Bellinger 2010, Nikolić 2010. In this study, the concept of a similar type of detector based on a porous Si matrix loaded with a fissile material, 235 U, was explored.…”

Si pillar structured thermal neutron detectors: fabrication challenges and performance expectations

“…The pillar pitch of 4 µm is defined lithographically to allow a high probability of interaction of the energetic ions with the semiconductor pillar. An efficiency of 20% [32] has been achieved with an array of etched Si pillars with 13:1 aspect ratio (2 x 2 µm 2 pillars with a 26 µm height and a separation of 2 µm) on a planar silicon substrate, arranged in a square matrix. One added benefit of this high-aspect-ratio design is that the so-called "streaming" of neutrons becomes negligible.…”