Query: Development of compact high efficiency microstructured semiconductor neutron detectors

Candidate papers:

abstract: Abstract Semiconductor diode detectors coated with neutron reactive materials are generally fashioned as planar diodes coated with 10B, 6LiF, or Gd. Planar detectors coated with 10B or 6LiF are limited to less than 5% intrinsic thermal neutron detection efficiency. Detectors coated with Gd can achieve higher efficiencies, but the low energy signatures are problematic in the presence of background radiations. Microstructured semiconductor neutron detectors (MSNDs) can now achieve a tenfold increase in neutron detection efficiency over the planar diode designs. These semiconductor neutron detectors are fashioned with a matrix of microstructured patterns etched deeply into the semiconductor substrate and, subsequently, backfilled with neutron reactive materials. Intrinsic thermal neutron detection efficiencies exceeding 35% have been achieved with devices no thicker than 1 mm while operating on less than 5 V, now allowing for instrumentation to be realized with similar performance as 3He gas filled detectors.
author_names: Douglas S Mcgregor

Steven L Bellinger

Ryan G Fronk

Luke C Henson

David E Huddleston

Taylor R Ochs

J Shultis

Timothy J Sobering

R D Taylor
title: Development of Compact High Efficiency Microstructured Semiconductor Neutron Detectors
year: 2015

abstract: Abstract High efficiency Microstructured Semiconductor Neutron Detectors (MSNDs) have been tiled and arranged in a cylindrical form factor in order to serve as a direct replacement to aging and increasingly expensive 3 He gas filled proportional neutron detectors. Two 6 in long by 2 in diameter cylinders were constructed and populated with MSNDs which were then directly compared to a 4 atm Reuter Stokes 3 He detector of the same dimensions. The Generation 1 MSND based 3 Helium Replacement (HeRep Mk I) device contained sixty four 1 cm 2 active area MSNDs, each with an intrinsic neutron detection efficiency of approximately 7% A Generation 2 device (the HeRep Mk II) was populated with thirty 4 cm 2 active area MSNDs, with an intrinsic thermal neutron detection efficiency of approximately 30% The MSNDs of each HeRep were integrated to count as a single device. The 3 He proportional counter and the HeRep devices were tested while encased in a cylinder of high density polyethylene measuring a total of 6 in by 9 in. The 3 He counter and the HeRep Mk II were each placed 1 m from a 54 ng 252 Cf source and tested for efficiency. The 3 He proportional counter had a net count rate of 17.13+ 0.10 cps at 1 m. The HeRep Mk II device had a net count rate of 17.60+ 0.10 cps, amounting to 102.71+ 2.65% of the 3 He gas counter while inside of the moderator. Outside of moderator, the 3 He tube had a count rate of 3.35+ 0.05 cps and the HeRep Mk II device reported 3.19+ 05, amounting to 95.15+ 9.04% of the 3 He neutron detector.
author_names: Ryan G Fronk

Steven L Bellinger

Luke C Henson

David E Huddleston

Taylor R Ochs

Timothy J Sobering

Douglas S Mcgregor
title: High efficiency microstructured semiconductor neutron detectors for direct 3He replacement
year: 2015

abstract: Silicon diodes with large aspect ratio 3D microstructures backfilled with 6LiF show a significant increase in neutron detection efficiency beyond that of conventional thin film coated planar devices. Described in this work are advancements in the technology using detector stacking methods and summed detector 6x6 element arraying methods to dramatically increase the sensitivity to thermal neutrons. The intrinsic detection efficiency of the 6x6 array for normal incident 0.0253 eV neutrons was found 6.8% compared against a calibrated 3He proportional counter.
author_names: Steven L Bellinger

Ryan G Fronk

Timothy J Sobering

Douglas S Mcgregor
title: High efficiency microstructured semiconductor neutron detectors that are arrayed, dual integrated, and stacked.
venue: Applied radiation and isotopes including data, instrumentation and methods for use in agriculture, industry and medicine
year: 2012

abstract: Dual Sided Microstructured Semiconductor Neutron Detectors (DS MSNDs) are continually being developed as a compact, low power, high efficiency alternative to 3He for thermal neutron detection. DS MSNDs are fabricated from 1.5 mm thick, 5 kOhm cm resistivity, silicon wafers. Deep trenches are etched into both sides of the silicon substrate with the back side trenches offset from the front side trenches to eliminate neutron free streaming paths through the silicon fins. A pvp type vertical diode is formed within the trench microstructures on both sides of the substrate. The trenches are then backfilled with 6LiF powder with powder packing fractions as high as 55% Incident neutrons are absorbed by 6Li atoms, which then fission and emit charged particle reaction products that can deposit energy in the adjacent silicon fins. Electron hole pairs created by the charged particle interactions are then drifted, and the current induced in the electrodes is integrated to form a voltage pulse that can be counted. So far, DS MSNDs have achieved detection efficiencies as high as 69.3% The present work describes efforts to improve the signal to noise ratio of the DS MSNDs to increase the gamma ray rejection ratio of the detectors. Silvaco TCAD simulations indicate alternative doping profiles can improve the charge collection efficiency and produce single polarity pulses regardless of interaction location, whereas the polarity of the previously reported DS MSND pulse was dependent on the location of the neutron interaction. Newly fabricated DS MSNDs will be used to populate Modular Radiation Detectors (MRD) which will be integrated into a high sensitivity Reconfigurable Wearable Detector (RWD) In addition to neutron detection, the MRDs will incorporate a high energy resolution gamma ray spectrometer for gamma ray source detection and identification. The RWD will be a highly versatile, low cost, low power, tool for the search, localization, and identification of radioactive material.
author_names: Taylor R Ochs

Jacob M Terrell

R M Hutchins

K Scott DeMint

Steven L Bellinger

Luke C Henson

Douglas S Mcgregor
title: Present Status of the Dual Sided Microstructured Semiconductor Neutron Detector (DS MSND) and Instrumentation
venue: 2019 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC)
year: 2019

abstract: Interest in high efficiency replacements for thin film coated thermal neutron detectors led to the development of single sided microstructured semiconductor neutron detectors (MSNDs) MSNDs are designed with micro sized trench structures that are etched into a vertically oriented pvnjunction diode, and backfilled with a neutron converting material, such as LiF. Neutrons absorbed by the converting material produce a pair of charged particle reaction products that can be measured by the diode substrate. MSNDs have higher neutron absorption and reaction product counting efficiencies than their thin film coated counterparts, resulting in up to a 10x increase in intrinsic thermal neutron detection efficiency. The detection efficiency for a single sided MSND is reduced by neutron streaming paths between the conversion material filled regions that consequently allow neutrons to pass undetected through the detector. Previously, the highest reported intrinsic thermal neutron detection efficiency for a single MSND was approximately 30% Methods for double stacking and aligning MSNDs to reduce neutron streaming produced devices with an intrinsic thermal neutron detection efficiency of 42% Presented here is a new type of MSND that features a complementary second set of trenches that are etched into the back side of the detector substrate. These dual sided microstructured semiconductor neutron detectors (DSMSNDs) have the ability to absorb and detect neutrons that stream through the front side, effectively doubling the detection efficiency of a single sided device. DS MSND sensors are theoretically capable of achieving greater than 80% intrinsic thermal neutron detection efficiency for a 1 mm thick device. Prototype DS MSNDs with diffused pvp junction operated at 0 V applied bias have achieved 53.54+ 0.61% exceeding that of the single sided MSNDs and double stacked MSNDs to represent a new record for detection efficiency for such solid state devices. Dual side etched microstructured semiconductor neutron detectors
author_names: Ryan G Fronk
title: Dual side etched microstructured semiconductor neutron detectors
year: 2017

abstract: Perforated semiconductor neutron detectors are compact diode detectors that operate at low power and can be fashioned to have high thermal neutron detection efficiency. Fabricated from high purity Si wafers, the perforations are etched into the diode surface with ICP RIE and backfilled with 6 LiF neutron reactive material. The intrinsic thermal neutron detection efficiency depends upon many factors, including the perforation geometry, size, and depth. Devices were fabricated from high resistivity 10 kO cm n type Si with conformal p type shallow junction diffusions into the perforations, which demonstrate improved neutron detection performance over previous selectively diffused designs. A comparison was made to previous selectively diffused designs, and pulse height spectra show improved signal to noise ratio, higher neutron counting efficiency, and excellent gamma ray discrimination. Devices with 20 daverageThmm wide 100mm deep sinusoidal trenches yielded intrinsic thermal neutron detection efficiencies of 11:9470:078%
author_names: Douglas S Mcgregor

Walter J McNeil

Steven L Bellinger

Troy C Unruh

J Shultis
title: Microstructured semiconductor neutron detectors
year: 2009

abstract: Microstructured semiconductor neutron detectors (MSNDs) represent a compact, low cost, high efficiency means of solid state thermal neutron detection. Trenches are etched into a 1 cm2 or 4 cm2 active area pn junction diode and backfilled with 6LiF neutron converting material. Charged particle reaction products produced from neutron capture within the conversion material can be measured to indicate the presence of neutrons. MSNDs can be arranged into larger instruments due to their small size, high efficiency, and low power consumption. A small, inexpensive electronics package named the `Domino' was developed to facilitate the deployment of the MSND(tm) technology. The Domino is a complete electronics package that supports a single MSND(tm) with all necessary signal processing electronics. The Domino electronics were tiled together to form large area arrays and portable detector arrays. Both were characterized with a small 252Cf source. A hand held portable `Briefcase' detector with 84 Dominoes(tm) forming a 30 cm x 38 cm array, weighed 21 lbs. A vehicle portable `Panel Array' detector with 480 Dominoes formed a 1 m x 1 m. For a bare 252Cf source, the `Briefcase' detector and the `Panel Array' detector yielded 0.27 0.01 cps ng 1 (at 2 m) and 0.45 0.01 cps ng 1 (at 5 m) respectively. Modified Domino packages (with upgraded MSNDs) were arranged into a 2 in. diameter, 6 in. long cylindrical form factor (HeRep Mk II) for direct 3He replacement, matching the efficiency of a 4 atm 3He with similar dimensions. A third generation helium replacement (HeRep Mk III) was constructed to replace more compact 3He form factors, with a 0.75 in. diameter and 4.5 in. length. Populated with dual sided MSNDs, this detector yielded 0.293 0.003 cps ng 1 for bare 252Cf at 0.2 m.
author_names: Ryan G Fronk

Steven L Bellinger

Luke C Henson

David E Huddleston

Taylor R Ochs

Michael A Reichenberger

Cody J Rietcheck

Colten T Smith

Timothy J Sobering

J Shultis

Douglas S Mcgregor
title: Advancements in microstructured semiconductor neutron detector (MSND) based instruments
venue: 2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC)
year: 2015

abstract: Perforated semiconductor neutron detectors are compact diode detectors that operate at low power and can be fashioned to have high thermal neutron detection efficiency. Fabricated from high purity Si wafers, the perforations are etched into the diode surface with ICP RIE and backfilled with LiF neutron reactive material. The intrinsic thermal neutron detection efficiency depends upon many factors, including the perforation geometry, size, and depth. Devices were fabricated from high resistivity 10 kO cm n type Si with conformal p type shallow junction diffusions into the perforations, which demonstrate improved neutron detection performance over previous selectively diffused designs. A comparison was made to previous selectively diffused designs, and pulse height spectra show improved signal to noise ratio, higher neutron counting efficiency, and excellent gamma ray discrimination. Devices with 20 daverageThmm wide 100mm deep sinusoidal trenches yielded intrinsic thermal neutron detection efficiencies of 11:9470:078% 2009 Elsevier B.V. All rights reserved.
author_names: Douglas S Mcgregor

Walter J McNeil

Steven L Bellinger

Troy C Unruh

J Shultis
title: Author s personal copy Microstructured semiconductor neutron detectors
year: 2009

abstract: There is an increased demand of neutron detectors for security applications requiring detection of special nuclear materials (SNMs) to prevent proliferation and illegitimate trafficking, for monitoring neutron beams, etc. [1][2] Commonly, 3 He and BF3 gas detectors are being used for such applications due their high efficiencies. However, these detectors suffer from certain issues such as global shortage of 3 He, toxicity of BF3, portability, etc. Therefore, in recent years, there has been a significant interest in the development of semiconductor based, mainly silicon based thermal neutron detectors as an alternative to these gas filled detectors. Silicon detectors have advantages of compactness, low operating voltage requirement and low cost due to well established fabrication technology and possibility of large scale production [2] Planar structured silicon based thermal neutron detectors, where a detector is coated or integrated with the converter material/layer (commonly 10 B due to high thermal neutron absorption cross section of 3800 barn) are reported to have maximum efficiency in the range 2 3% This low efficiency is the consequence of limitations on convertor material/layer thickness due to self absorption of the secondary charged particles produced in the interaction of neutron with converter material 10 B (n, a) 7 Li) One of the ways for improving the efficiency of silicon based neutron detector is to increase the thickness of 10 B by making the trenches or array of pillars filled with 10 B. We have initiated the development of a high efficiency 3D structured thermal neutron detector having array of PIN diode pillars filled with 10 B. Initial simulation results for optimizing the geometrical parameters of the 3D pillar structured thermal neutron detector are presented in this paper. Simulation studies
author_names: Ashutosh Kumar Singh

Anita Topkar
title: Simulation studies for optimization of geometrical parameters of 3D neutron detectors
year: 2020

abstract: Low power microstructured semiconductor neutron detector (MSND) devices have long been investigated as a high efficiency replacement for thin film diodes for solid state thermal neutron detection. Improvements in detection efficiency were made by integrating two stacked 1 cm2 devices to function as a single detector, achieving over 42% intrinsic thermal neutron detection efficiency. The need for larger active area devices led to the development of the Arrayed Device which combined seventy two dual stacked 1 cm2 devices to act as a single large area detector in a 6x6 configuration, providing an active detector area of 36 cm2. A new development in large active area devices has led to high quality 4 cm2 individual devices arrayed into a detector array comprised of 16 of individual perforated devices, at 64 cm2, providing a 78% increase in active area over the previously reported 6x6 element. Nine of the 4x4 4 cm2 elements are then integrated together into the Very Large Area Panel Array (VLAPA) with total device dimensions of 11.125"x11.125"x0.5" without moderator. The elements work to function as a single VLAPA with an effective active detection area of 576 cm2. The VLAP A has been found to have an intrinsic efficiency of 2.21+ 0.02% with 2 inches HDPE on the front and back for an unmoderated 252Cf source.
author_names: Steven L Bellinger

B William Cooper

Nathanial R Crawford

Ryan G Fronk

Timothy J Sobering

Russell D Taylor

Douglas S Mcgregor
title: Very large area multi element microstructured semiconductor neutron detector panel array
venue: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC)
year: 2012