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Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Neutron spectrometry can play an important role in the detection and identification of neutron-emitting sources in various security applications. In the present work, a portable filtered array neutron spectrometer, consisting of twelve 6LiF-based thermal neutron detectors embedded within a single heterogeneous volume was designed and its expected performance compared to that of a commercially available 12-sphere Bonner spheres spectrometer. Each detector within the volume was designed to optimally respond to a unique portion of the neutron spectrum by varying the type and thickness of materials used to filter the spectrum as well as the thickness of the moderator in front of the detector. The available design space was permuted and performance metrics developed to identify the optimal geometries. The top performing detector geometries were then combinatorially explored to identify the best array of geometries that yielded the most information about a neutron spectrum. The best performing filtered array was found to provide as much spectral information as, or more than, the commercially available 12-sphere Bonner spheres spectrometer to which it was compared.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Neutron spectrometry can play an important role in the detection and identification of neutron-emitting sources in various security applications. In the present work, a portable filtered array neutron spectrometer, consisting of twelve 6LiF-based thermal neutron detectors embedded within a single heterogeneous volume was designed and its expected performance compared to that of a commercially available 12-sphere Bonner spheres spectrometer. Each detector within the volume was designed to optimally respond to a unique portion of the neutron spectrum by varying the type and thickness of materials used to filter the spectrum as well as the thickness of the moderator in front of the detector. The available design space was permuted and performance metrics developed to identify the optimal geometries. The top performing detector geometries were then combinatorially explored to identify the best array of geometries that yielded the most information about a neutron spectrum. The best performing filtered array was found to provide as much spectral information as, or more than, the commercially available 12-sphere Bonner spheres spectrometer to which it was compared.
Author: Eliot R. Myers Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 147
Book Description
The detection of special nuclear material (SNM) is no trivial task; the low activity of isotopes such as 235U and the ease of shielding make their passive detection virtually impossible in the maritime environment. Active interrogation, while increasing the radiative signature, also increases the radiative background such that measuring SNM signatures becomes difficult, if not impossible, especially given an unknown and complex environment. Over the last two decades, numerous active interrogation methods and technologies have been proposed, many of which reduce or filter the relevant background by interrogating one type of radiation and measuring another type or property domain. However, by focusing on single properties of the SNM signature (e.g. time or energy) in laboratory conditions, the effectiveness of these methods in dynamic and unknown environments remains inadequate. In order for a method—or combination of methods—to be effective, it must be able to incorporate as much of the SNM signature as possible into the measurement, including the signature’s energy, time, and directional (or spatial) properties. The first part of this thesis provides a review of these methods and their limitations with an emphasis on outlining all of the SNM signature properties available to active interrogation applications. The second part discusses two improvements to multi-detector moderating neutron spectrometers in order to exploit all of these SNM signature parameters: time, energy, and space. The two new methods are: 1) an energy-specific optimization method for application driven spectrometer design via virtual detector simulations and genetic algorithms, and 2) a neutron response vectorization method for determining neutron source location by vectorizing the moderating neutron response functions. Although these new approaches by no means solve the problem of SNM detection, they provide a crucial step in tailoring moderating spectrometers to detecting the SNM signature, upon which future works can expand.
Author: Simon R. Bolding Publisher: ISBN: Category : Languages : en Pages :
Book Description
Simulations were performed using MCNP5 to optimize the geometry of a neutron spectrometer. The cylindrical device utilizes micro-structured neutron detectors encased in polyethylene moderator to identify sources based on energy spectrum. Sources are identified by comparison of measured detector responses to predetermined detector response templates that are unique to each neutron source. The design of a shadow shield to account for room scattered neutrons was investigated as well. For sufficient source strength in a void, the optimal geometric design was able to detect all sources in 1000 trials, where each trial consists of simulated detector responses from 11 unique sources. When room scatter from a concrete floor was considered, the shadow shield corrected responses were capable of correctly identifying 96.4% of the simulated sources in 1000 trials using the same templates. In addition to spectrometer simulations, a set of neutron multiplicity experiments from a plutonium sphere with various reflector thicknesses were simulated. Perturbations to nuclear data were made to correct a known discrepancy between multiplicity distributions generated from MCNP simulations and experimental data. Energy-dependent perturbations to the total number of mean neutrons per fission [average velocity] of 239Pu ENDF/B-VII. 1 data were analyzed. Perturbations were made using random samples, correlated with corresponding covariance data. Out of 500 unique samples, the best-case [average velocity] data reduced the average deviation in the mean of multiplicity distributions between simulation and experiment to 4.32% from 6.73% for the original data; the average deviation in the second moment was reduced from 13.87% to 8.74%. The best-case [average velocity] data preserved k[subscript]e[subscript]f[subscript]f with a root-mean-square deviation (RMSD) of 0.51% for the 36 Pu cases in the MCNP validation suite, which is comparable to the 0.49% RMSD produced using the original nuclear data. Fractional shifts to microscopic cross sections were performed and multiplicity and criticality results compared. A 1.5% decrease in fission cross section was able to correct the discrepancy in multiplicity distributions greater than the [average velocity] perturbations but without preserving k[subscript]e[subscript]f[subscript]f.
Author: Cory Blake Hoshor Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 182
Book Description
Measuring neutron source‐dependent free neutron properties over a large neutron energy range, with human‐portable instrumentation, continues to push the frontier of neutron detection instrumentation design and analysis techniques. In addition, a variety of nuclear nonproliferation and health physics applications require instrumentation that can provide free neutron property measurement and analysis in real time. To overcome the challenges inherent to these applications and advance the state of the current art in neutron detection instrumentation, the first representatives of a new class of solid-state moderating-type neutron spectrometer have been designed, modeled, fabricated, and tested. This work introduces state-of-the-art human-portable instruments by discussing the fundamental theory of their operation, investigating and analyzing—via Monte Carlo simulation—the principle considerations for optimal instrument design, and empirically evaluating the capability of each of the fabricated spectrometers to meet the application needs. Utilizing the unique three dimensional neutron thermalization information afforded by this new class of instrumentation, novel algorithmic methodologies are introduced to determine free neutron characteristics of interest to the aforementioned applications in real time.
Author: Thomas Martin Publisher: ISBN: Category : Languages : en Pages :
Book Description
The measurement of the distribution of kinetic energy carried by neutron particles is of interest to the health physics and radiation protection industry. Neutron particle spectral fluence is essential to the calculation of absorbed dose, equivalent dose, and other dosimetric quantities . Current methods of neutron spectrometry require either a large number of individual measurements and a priori spectral information, or complex and delicate equipment. To reduce these deficiencies, a novel neutron spectrometer, consisting of plastic scintillating fibers in a hexagonal array, was simulated via Monte Carlo. Fiber size and boron content were varied to optimize response characteristics. The results were compared to industry standard multi-sphere spectrometers. Of the geometries and materials analyzed, it was found that smaller diameter fibers with 1% loading of natural boron provide the best efficiency and energy resolution. Energy resolution was found to be similar to multi-sphere spectrometers, with the ability to differentiate on the order of ten energy fluence groups. Near isotropic angular response was traded for significantly reduced detection time and increased simplicity. Spectral analysis of individual fiber response can provide directional information based on the ratio of energy deposition by thermal neutrons to all neutrons. Future work using proton recoil spectral data from individual fibers will allow increases in energy resolution while reducing or eliminating the need for a priori spectral information.
Author: International Atomic Energy Agency Publisher: IAEA Radiation Technology Repo ISBN: 9789201251107 Category : Science Languages : en Pages : 145
Book Description
This publication addresses recent developments in neutron generator (NG) technology. It presents information on compact instruments with high neutron yield to be used for neutron activation analysis (NAA) and prompt gamma neutron activation analysis in combination with high count rate spectrometers. Traditional NGs have been shown to be effective for applications including borehole logging, homeland security, nuclear medicine and the on-line analysis of aluminium, coal and cement. Pulsed fast thermal neutron analysis, as well as tagged and timed neutron analysis, are additional techniques which can be applied using NG. Furthermore, NG can effectively be used for elemental analysis and is also effective for analysis of hidden materials by neutron radiography. Useful guidelines for developing NG based research laboratories are also provided in this publication.
Author: R. Winter Publisher: Springer Science & Business Media ISBN: 9401116997 Category : Science Languages : en Pages : 639
Book Description
This monograph, which is the outcome of the ASI on High Pressure Chemistry, Biochemistry, and Materials Science, illustrates new developments in the field of high pressure science. In fact, for chemists, biochemists, and materials scientists, pressure as an experimental variable represents a tool which provides unique information about systems of materials studied. It is interesting to note how the growth of the high pressure field is also reflected in the content of the recent ASI's dealing with this field. The ASI High Pressure Chemistry held in 1977 was followed by the ASI High Pressure Chemistry and Biochemistry held in 1986, and the coverage of the present ASI also includes applications to materials science. In view of the teaching character of the ASI, it is natural that main contributions to this volume present overviews of the different subfields or applications of high pressure research. In contrast, contributed papers offer more specialized aspects of various high pressure studies. The various contributions to this volume make clear the impressive range of fundamental and applied problems that can be studied by high pressure techniques, and also point towards a major growth of high pressure science and technology in the near future. This ASI focused mainly on advances achieved in the six years since the previous ASI devoted to the high pressure field. The organization of this volume is as follows.
Author: 
Author: 
Author: Eliot R. Myers
Author: Simon R. Bolding
Author: Cory Blake Hoshor
Author: Thomas Martin
Author: International Atomic Energy Agency
Author: J. M. Carpenter
Author: R. Winter
Author: 
Author: A. J. Dianoux