Papers by Douglas McGregor
Fundamentals of Semiconductor Detectors for Ionizing Radiation
MRS Online Proceeding Library
ABSTRACT
HENDA and Patara: A Solid State Neutron Detector and a Prototype Readout Chip for the SNS
Nuclear Instruments and Methods
The present work employs MSND technology as a 3 He gas-tube direct-replacement technology. The MS... more The present work employs MSND technology as a 3 He gas-tube direct-replacement technology. The MSND-based Helium Replacement (HeRep) is a single instrument utilizing thirty 4-cm 2 active area MSNDs to directly replace 3 He-based proportional neutron counters. The HeRep Mk II prototype yielded 102.71±0.84% of the neutron detection efficiency of a 4-atm Reuter Stokes 3 He gas-filled detector with the same active dimensions and test setup from a 252 Cf source. The HeRep Mk II matched the efficiency of the 3 He detector while using MSNDs that each had 20% intrinsic-efficiency for thermal-neutrons.
2011 IEEE Nuclear Science Symposium Conference Record, 2011
Low-power microstructured semiconductor neutron detector (MSND) devices have lon g been investi g... more Low-power microstructured semiconductor neutron detector (MSND) devices have lon g been investi g ated as a hi g h-efficiency replacement for thin-film diodes for thermal neutron detection. The detector devices were improved by stackin g two tcm 2 devices and inte g ratin g their responses to g ether to act as a sin g le diode, increasin g detection efficiency to over 42%. The need for lar g er active area devices has driven further improvement of the technolo g y. A lar g e active area device has been developed by arrayin g seventy-two tcm 2 devices to g ether into two 6x6 confi g urations, dual-stackin g them, and
IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium
Perforated semiconductor neutron detectors are compact, high-efficiency, diode detectors that ope... more Perforated semiconductor neutron detectors are compact, high-efficiency, diode detectors that operate at low power. Microstructured neutron detector fabrication methods have been improved over previous manufacturing methods. The neutron detectors are easily fabricated from high purity n-type Si, in which patterned trenches are etched into the Si substrate, wherein shallow p-type junctions are diffused. The trenches are then backfilled with 6LiF powder, making the devices sensitive to reaction products from the 6Li(n,t)3He reaction. Pulse height spectra show improved signal-to-noise ratio, higher neutron counting efficiency, and excellent gamma-ray discrimination over previous microstructured neutron detector designs. Thermal neutron detection measurements from a 0.0253 eV diffracted neutron beam, yielded 20.4% intrinsic detection efficiency for devices with 245 micron deep trenches and 21% intrinsic detection efficiency for two back-to-back devices each having 113 micron deep trenches.
A Solid State, Position Sensitive GaAs Device as a Neutron Camera
Prototype thermal neutron imaging arrays have been fabricated from semi-insulating (SI) bulk GaAs... more Prototype thermal neutron imaging arrays have been fabricated from semi-insulating (SI) bulk GaAs. The arrays are 1 mm square Schottky diodes arranged in a 5 x 5 matrix. GaAs Schottky barrier radiation detectors are relatively radiation hard and can withstand higher neutron and gamma ray exposure fields than MOS-based Si diode imaging arrays. The devices use ' OB to convert incident thermal neutrons to energetic Li ions and alpha particles. The truncated field effect observed with SI bulk GaAs detectors produces high and low field regions in the device. Electron-hole pairs produced in the active (or high field) region of the device contribute to the observed induced charge, whereas electron-hole pairs produced in the low field region contribute very little to the induced charge. The effect is manipulated to reduce the background gamma ray interaction rate in the devices. Preliminary results show no indication of device degradation after exposure to a total thermal neutron fluence of 1.73 x l0l3 n/cm2. Images have been formed of 1, 1.5, and 2 mm holes and crosses from 2 mm thick Cd templates.
Development of Compact High Efficiency Microstructured Semiconductor Neutron Detectors
Radiation Physics and Chemistry
Semiconductor diode detectors coated with neutron reactive materials are generally fashioned as p... more 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 (MSND) 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 volts, now allowing for instrumentation to be realized with similar performance as 3He gas...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
A technology that makes use of recently developed high-efficiency, low-power semiconductor detect... more A technology that makes use of recently developed high-efficiency, low-power semiconductor detectors for neutron dosimetry is described. Silicon semiconductor material is perforated using plasma etching techniques; the surface is then coated and the perforations are filled with neutron reactive material. These perforated detectors appear to be capable of greater than 40% efficiency when used in a sandwich design. Devices incorporating bare and cadmium-filtered perforated semiconductor detectors with micro-controller hardware to process and readout the detectors can be made small enough to function as portable neutron dosimeters. Monte Carlo modeling that relates the detector responses to phantom dose equivalent at various positions on an elliptical water phantom is discussed.
Non-streaming high-efficiency perforated semiconductor neutron detectors, method of making same a... more Non-streaming high-efficiency perforated semiconductor neutron detectors, method of making same and measuring wands and detector modules utilizing same are disclosed. The detectors have improved mechanical structure, flattened angular detector responses, and reduced leakage current. A plurality of such detectors can be assembled into imaging arrays, and can be used for neutron radiography, remote neutron sensing, cold neutron imaging, SNM monitoring, and various other applications.
Method of Fabricating a Neutron Detector such as a Microstructured Semiconductor Neutron Detector
The present work employs MSND technology as a He-3 gas-tube direct-replacement technology. The MS... more The present work employs MSND technology as a He-3 gas-tube direct-replacement technology. The MSND-based Helium Replacement (HeRep) is a single instrument utilizing thirty 4-cm2 active area MSNDs to directly replace 3He-based proportional neutron counters. The HeRep Mk II prototype yielded 102.71+-0.84% of the neutron detection efficiency of a 4-atm Reuter Stokes 3He gas-filled detector with the same active dimensions and test setup from a Cf-252 source. The HeRep Mk II met the efficiency of the 3He detector while using MSNDs that had 20% intrinsic-efficiency for thermal-neutrons.
Charge collection efficiency (CCE) mapping was performed by simulating a 5.0 x 5.0 x 10.0 mm3 Fri... more Charge collection efficiency (CCE) mapping was performed by simulating a 5.0 x 5.0 x 10.0 mm3 Frisch-collared BiI3 gamma-ray detector with an applied bias of 4800V and comparing the results to those previously published for a 4.7 x 4.7 x 9.5 mm3 Frisch-collared CdZnTe device with an applied bias of 1200V. The BiI3 mobility-lifetime products used for CCE mapping were μeτe = 9.5 x 10-6 cm2 V-1 and μhτh = 1.0 x 10-7 cm2 V-1 for electrons and holes, respectively. The simulations were performed using the modified form of the Hecht equation and the necessary weighting-potential and weighting-field distributions were simulated using the commercially available software package COULOMB. After comparing the simulation results to CdZnTe, the applied bias and mobility-lifetime products were adjusted separately until the Frisch-collared BiI3 device resembled the CCE of the CdZnTe Frisch-collared device. Using the previously stated mobility-lifetime products, an applied bias of 2.1 MV is necessar...
Improved Efficiency for Gas-Filled Neutron Detectors Through Compartmentalization
CdZnTe semiconductor parallel Frisch grid radiation detectors
1997 IEEE Nuclear Science Symposium Conference Record, 1997
Position-dependent free charge carrier losses during transport can prevent efficient charge carri... more Position-dependent free charge carrier losses during transport can prevent efficient charge carrier extraction from semiconductor detectors and severely reduce energy resolution. Hole trapping losses in CdZnTe radiation detectors are far worse than electron trapping losses and resolution degradation in CdZnTe detectors results primarily from severe hole trapping during transport. Coplanar radiation detectors improve energy resolution by sensing the induced charge
<title>Characteristics of the stacked microstructured solid state neutron detector</title>
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XII, 2010
ABSTRACT Silicon diodes with large aspect ratio perforated microstructures backfilled with 6LiF s... more ABSTRACT Silicon diodes with large aspect ratio perforated microstructures backfilled with 6LiF show a dramatic increase in neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology with increased microstructure depths and detector stacking methods that work to increase thermal-neutron detection efficiency. Models for ion energy deposition and intrinsic thermal-neutron detection efficiency for the straight trench design are described and results presented. A dual stacked device was fabricated by coupling two detectors back-to-back, along with counting electronics, into a single detector. Experimentally verified results and modeled predictions are compared. The stacked device delivered 37% intrinsic thermal-neutron detection efficiency, lower than the predicted value of 47%. It was determined that this lower observed efficiency is due to detector misalignment in the stacked structure and ballistic deficit from slow charge collection from the deep trench structures. The intrinsic thermal-neutron detection efficiency depends strongly upon the geometry, size, and depth of the perforated microstructures. This work is part of on-going research to develop solid-state semiconductor neutron detectors with high detection efficiencies.
3D real-time in-core neutron flux mapping with micro-pocket fission detectors (MPFD)
2007 IEEE Nuclear Science Symposium Conference Record, 2007
ABSTRACT A micro-pocket fission detector (MPFD) array is being deployed in the Kansas State Unive... more ABSTRACT A micro-pocket fission detector (MPFD) array is being deployed in the Kansas State University TRIGA Mark-II nuclear reactor in order to produce a real-time 3-dimensional neutron flux map. A total of 75 MPFD3-Ts make up the array where each MPFD3-T consists of an uncoated detector for background subtraction, a 93% enriched 235U coated detector for thermal neutron sensitivity, a natural uranium coated detector for mixed energy neutron sensitivity, and a thermocouple for thermal monitoring. The array is located in fixed in-core positions between fuel elements and is capable of being read out in pulse, MSV, and current modes allowing for operation from shutdown to full power. In addition, using off-the-shelf electronic components, the system is able to track reactor pulses with power changes spanning 7 orders of magnitude in less than 100 milliseconds.
2006 IEEE Nuclear Science Symposium Conference Record, 2006
Excessive leakage current in perforated pin diodes was identified and addressed through simple ch... more Excessive leakage current in perforated pin diodes was identified and addressed through simple changes in processing techniques. The first pulse height spectra from a perforated diode operated as a radiation detector is reported. Also, methods to load 6 LiF neutron absorbing material into deep perforations are reported.
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Papers by Douglas McGregor