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Author: Taylor R. Ochs Publisher: ISBN: Category : Languages : en Pages :
Book Description
Dual-Sided Microstructured Semiconductor Neutron Detectors (DS-MSNDs) have been developed as a viable alternative to expensive 3He for thermal-neutron detection. DS-MSNDs were designed as an advancement on single-sided MSNDs which comprise high-aspect ratio trenches backfilled with 6LiF neutron conversion material etched deep into silicon pvn-junction diodes. Neutrons react in the conversion material, which produces energetic charged-particle reaction products that are measured in the adjacent silicon microfeatures. Single-sided MSNDs have been produced with an intrinsic thermal-neutron detection efficiency of 30-35% for normally incident neutrons, and the key limiting factor in detection efficiency is neutron free streaming paths through the neutron insensitive silicon fins. The DS-MSND incorporates a second set of 6LiF-backfilled trenches etched on the back-side of a thicker silicon diode that are offset from the front-side trenches to eliminate the neutron free streaming paths. Monte Carlo simulations show DS-MSNDs only 1.5-mm thick are theoretically capable of 80% intrinsic thermal-neutron detection efficiency, which could directly match commonly available 3He detectors. This work describes the design of DS-MSNDs including electric field modeling and microfeature geometry optimization with MCNP simulations, and fabrication process improvements implemented that elevate the state-of-the-art. The previous world record for intrinsic thermal-neutron detection efficiency for semiconductor neutron detectors was 53.5 ± 0.6%. Advancements in deep-trench etching and 6LiF backfilling methods presented herein have increased the current record intrinsic-thermal neutron detection efficiency to 69.3 ± 1.5%. Several prototype detector systems were fabricated implementing DS-MSND and MSND technology to aid in search and localization of special nuclear material. Drop-in replacements for small-diameter, high-pressure 3He detectors, and the DS-MSND-based HeRep Mk IV measured 80% to 115% of the count rate of a similarly sized 10-atm 3He detector based on the detector and source moderation configuration. Additionally, modular neutron detectors were developed for use in a high-sensitivity, low profile, wearable neutron detector for covert or overt source detection missions by warfighters, first responders, or law enforcement personnel. Additionally, MCNP simulations show the wearable detectors have potential to as operate as high-accuracy, real-time, neutron dose meters. The DS-MSND-based detector systems with on-board electronics offer a low-cost, low-power, compact, high sensitivity, alternative to 3He neutron detection.
Author: Taylor R. Ochs Publisher: ISBN: Category : Languages : en Pages :
Book Description
Dual-Sided Microstructured Semiconductor Neutron Detectors (DS-MSNDs) have been developed as a viable alternative to expensive 3He for thermal-neutron detection. DS-MSNDs were designed as an advancement on single-sided MSNDs which comprise high-aspect ratio trenches backfilled with 6LiF neutron conversion material etched deep into silicon pvn-junction diodes. Neutrons react in the conversion material, which produces energetic charged-particle reaction products that are measured in the adjacent silicon microfeatures. Single-sided MSNDs have been produced with an intrinsic thermal-neutron detection efficiency of 30-35% for normally incident neutrons, and the key limiting factor in detection efficiency is neutron free streaming paths through the neutron insensitive silicon fins. The DS-MSND incorporates a second set of 6LiF-backfilled trenches etched on the back-side of a thicker silicon diode that are offset from the front-side trenches to eliminate the neutron free streaming paths. Monte Carlo simulations show DS-MSNDs only 1.5-mm thick are theoretically capable of 80% intrinsic thermal-neutron detection efficiency, which could directly match commonly available 3He detectors. This work describes the design of DS-MSNDs including electric field modeling and microfeature geometry optimization with MCNP simulations, and fabrication process improvements implemented that elevate the state-of-the-art. The previous world record for intrinsic thermal-neutron detection efficiency for semiconductor neutron detectors was 53.5 ± 0.6%. Advancements in deep-trench etching and 6LiF backfilling methods presented herein have increased the current record intrinsic-thermal neutron detection efficiency to 69.3 ± 1.5%. Several prototype detector systems were fabricated implementing DS-MSND and MSND technology to aid in search and localization of special nuclear material. Drop-in replacements for small-diameter, high-pressure 3He detectors, and the DS-MSND-based HeRep Mk IV measured 80% to 115% of the count rate of a similarly sized 10-atm 3He detector based on the detector and source moderation configuration. Additionally, modular neutron detectors were developed for use in a high-sensitivity, low profile, wearable neutron detector for covert or overt source detection missions by warfighters, first responders, or law enforcement personnel. Additionally, MCNP simulations show the wearable detectors have potential to as operate as high-accuracy, real-time, neutron dose meters. The DS-MSND-based detector systems with on-board electronics offer a low-cost, low-power, compact, high sensitivity, alternative to 3He neutron detection.
Author: Ryan G. Fronk Publisher: ISBN: Category : Languages : en Pages :
Book Description
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 pvn-junction diode, and backfilled with a neutron converting material, such as 6LiF. 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 (DS-MSNDs) 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.
Author: Steven Lawrence Bellinger Publisher: ISBN: Category : Languages : en Pages :
Book Description
The microstructured semiconductor neutron detector (MSND) was investigated and previous designs were improved and optimized. In the present work, fabrication techniques have been refined and improved to produce three-dimensional microstructured semiconductor neutron detectors with reduced leakage current, reduced capacitance, highly anisotropic deep etched trenches, and increased signal-to-noise ratios. As a result of these improvements, new MSND detection systems function with better gamma-ray discrimination and are easier to fabricate than previous designs. In addition to the microstructured diode fabrication improvement, a superior batch processing backfill-method for 6LiF neutron reactive material, resulting in a nearly-solid backfill, was developed. This method incorporates a LiF nano-sizing process and a centrifugal batch process for backfilling the nanoparticle LiF material. To better transition the MSND detector to commercialization, the fabrication process was studied and enhanced to better facilitate low cost and batch process MSND production. The research and development of the MSND technology described in this work includes fabrication of variant microstructured diode designs, which have been simulated through MSND physics models to predict performance and neutron detection efficiency, and testing the operational performance of these designs in regards to neutron detection efficiency, gamma-ray rejection, and silicon fabrication methodology. The highest thermal-neutron detection efficiency reported to date for a solid-state semiconductor detector is presented in this work. MSNDs show excellent neutron to gamma-ray (n/[gamma]) rejection ratios, which are on the order of 106, without significant loss in thermal-neutron detection efficiency. Individually, the MSND is intrinsically highly sensitive to thermal neutrons, but not extrinsically sensitive because of their small size. To improve upon this, individual MSNDs were tiled together into a 6x6-element array on a single silicon chip. Individual elements of the array were tested for thermal-neutron detection efficiency and for the n/[gamma] reject ratio. Overall, because of the inadequacies and costs of other neutron detection systems, the MSND is the premier technology for many neutron detection applications.
Author: Diego Laramore Publisher: ISBN: Category : Languages : en Pages :
Book Description
A semiconductor neutron imaging device is proposed (X-MSND) based on high efficiency, Micro-structured Semiconductor Neutron Detector (MSNDs) bump bonded onto a Timepix pixelated readout chip. The device serves as a combined neutron and photon imager with a 256x256 pixel array, using per-pixel time-over-threshold (ToT) energy deposition. The X-MSND design has produced thermal neutron detection efficiency of 14%, significantly greater than the theoretical maximum of less than 5% for planar devices. Simulated pixel clusters showed similar qualitative characteristics as planar neutron sensitive Timepix hybrid detectors. A workflow for simulating the semiconductor physics, ionization by radiation, and charge carrier transport for micro-structured sensors in general has been devised and described in this work. The simulation workflow began by steady state initial conditions of the X-MSND PIN diode sensor at full bias using COMSOL Multiphysics. This simulation step served the combined purpose of providing the necessary electric field solutions used in charge transport, and provided necessary design and operating parameters for device fabrication. Radiation transport code Geant4 was used to simulate the radiation detection characteristics of the sensor: thermal neutron detection efficiency, energy deposition per detection event, and the location of the ionized charge cloud per interaction are all calculated at this step. Dassault SolidWorks was used to generate Computer-Assisted Drafting (CAD) models of the full micro-structured device geometry, which was then converted and imported into a format that can be interpreted by Geant4 for the radiation transport. Geant4 can then interface directly with a modified version of Allpix^2 to perform charge carrier drift over the entire X-MSND geometry. Fabricated X-MSND devices were tested and evaluated at Kansas State University (KSU), and were found capable of producing high quality radiographs with both X-rays and neutrons. The fabrication of functioning X-MSND/Timepix assemblies was a collaborative effort among several research groups at KSU, domestic and international industrial partners, and international research groups. Fabrication of the X-MSND sensors was performed largely by Radiation Detection Technologies, Inc., with parametric design support from the Radiological System Integration Laboratory (RSIL) and Radiological Engineering Analysis Laboratory (REAL). The processes used in the production of X-MSND sensors are conventional micro-electro-mechanical system (MEMS) photolithography techniques; spin-on deposition and ultraviolet development of photoresist, metal lift-off, and wet etching of silicon are all used over the course of fabrication, and are described in detail. The Electronics Design Laboratory (EDL) of Kansas State University assisted in the design of custom printed circuit boards to which the X-MSND/Timepix assemblies are mounted. External to facilities located at KSU, various industrial manufacturing partners who specialize in Very Large Scale Integration (VLSI) and micro-fabrication assembly processes were also contracted to perform the specialized assembly processes required in assembling the full X-MSND/Timepix systems.
Author: Yacouba Diawara Publisher: Springer Nature ISBN: 3031365461 Category : Science Languages : en Pages : 257
Book Description
This book covers the most common neutron detectors used in neutron scattering facilities and all of those in use at Oak Ridge National Lab. It starts describing the facilities, instruments and the critical detector parameters needed by various instruments. Then the key components of the 3He-based linear position-sensitive detectors as well as on their electronics, which require particular attention to signal processing and noise reduction, are introduced. One chapter is dedicated to the 3He alternatives where scintillators play a critical role. It also covers emerging neutron detection technologies including semiconductors, vacuum-based devices and their associated readouts, which will be required in the future for high rate and high-resolution neutron detectors. The authors explain the logic behind the choice of materials as well as the various constraints that neutron detectors must respect to be useful. Some of these constraints, such as efficiency and gamma-ray sensitivity are common to all neutron counters while others, like timing resolution, dynamic range, and peak counting rate, depend on the applications. The book guides experts, the nuclear science community, and young scholars through the physical processes and the required electronics in a way that is accessible for those not professionally involved in designing detector’s components and electronic circuits.
Author: Wenkai Fu Publisher: ISBN: Category : Languages : en Pages :
Book Description
The Transient REActor Test (TREAT) facility was restarted and will be used to test accident-tolerant fuels to improve nuclear reactor safety. In this work, alternative neutron detectors for use in core and with the hodoscope at the TREAT facility were modeled and simulated using different computational tools to understand the underlying physics. The Hornyak button scintillation detector used in the original TREAT hodoscope to detect fast neutrons and its variants were evaluated using Geant4 to simulate the coupled nuclear and optical physics. The Hornyak-button model predicted an intrinsic efficiency of 0.35% for mono-directional fission neutrons and strong gamma-induced Cherenkov noise, which agree relatively well with the reported experimental observations. The proposed variants use silicon photomultipliers to reduce Cherenkov noise and have optimized layered or homogenized scintillation volumes. The layered and homogenized variants with 5-cm length were predicted to achieve neutron-detection efficiencies of 3.3% and 1.3%, respectively, at a signal-to-noise ratio of 100. Another candidate devices for the hodoscope are the actinide and hydrogenous microstructured semiconductor neutron detectors (MSNDs) evaluated using Geant4 and MCNP. With a sufficient rejection of the gamma noises, the U235 -filled and the hydrogenous MSNDs were predicted to yield neutron-detection efficiencies of 1.2% and 2.5%, respectively, at the length of 2 cm. The micro-pocket fission detectors (MPFDs) were developed to detect in-core neutrons, and the electron collection process in such devices was evaluated using Garfield++-based computational routine. The high-performance Garfield++ application was developed using the built-in, optimized element-search techniques and a hydrid MPI and OpenMP parallelization scheme. The preliminary results indicated that the averaged deposited energy per fission fragment was 7.15 MeV, and the induced current occured within 400 ns.
Author: Taylor R. Ochs
Author: Taylor R. Ochs
Author: Ryan G. Fronk
Author: Steven Lawrence Bellinger
Author: Diego Laramore
Author: Yacouba Diawara
Author: A. Chesavage
Author: Adam D. Weltz
Author: Wenkai Fu
Author: Siddartha Srinivasan Nandagopala Krishnan
Author: Ian Suttie