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: Publisher: ISBN: Category : Languages : en Pages : 25
Book Description
The heightened focus on nuclear safeguards and accountability has increased the need to develop and verify simulation tools for modeling these applications. The ability to accurately simulate safeguards techniques, such as neutron multiplicity counting, aids in the design and development of future systems. This work focuses on validating the ability of the Monte Carlo code MCNPX-PoliMi to reproduce measured neutron multiplicity results for a highly multiplicative sample. The benchmark experiment for this validation consists of a 4.5-kg sphere of plutonium metal that was moderated by various thicknesses of polyethylene. The detector system was the nPod, which contains a bank of 15 3He detectors. Simulations of the experiments were compared to the actual measurements and several sources of potential bias in the simulation were evaluated. The analysis included the effects of detector dead time, source-detector distance, density, and adjustments made to the value of [nu]-bar in the data libraries. Based on this analysis it was observed that a 1.14% decrease in the evaluated value of [nu]-bar for 239Pu in the ENDF-VII library substantially improved the accuracy of the simulation.
Author: Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
A transportable fast neutron detection system has been designed and constructed for measuring neutron energy spectra and flux ranging from tens to hundreds of MeV. The transportability of the spectrometer reduces the detector-related systematic bias between different neutron spectra and flux measurements, which allows for the comparison of measurements above or below ground. The spectrometer will measure neutron fluxes that are of prohibitively low intensity compared to the site-specific background rates targeted by other transportable fast neutron detection systems. To measure low intensity high-energy neutron fluxes, a conventional capture-gating technique is used for measuring neutron energies above 20 MeV and a novel multiplicity technique is used for measuring neutron energies above 100 MeV. The spectrometer is composed of two Gd containing plastic scintillator detectors arranged around a lead spallation target. To calibrate and characterize the position dependent response of the spectrometer, a Monte Carlo model was developed and used in conjunction with experimental data from gamma ray sources. Multiplicity event identification algorithms were developed and used with a Cf-252 neutron multiplicity source to validate the Monte Carlo model Gd concentration and secondary neutron capture efficiency. The validated Monte Carlo model was used to predict an effective area for the multiplicity and capture gating analyses. For incident neutron energies between 100 MeV and 1000 MeV with an isotropic angular distribution, the multiplicity analysis predicted an effective area of 500 cm2 rising to 5000 cm2. For neutron energies above 20 MeV, the capture-gating analysis predicted an effective area between 1800 cm2 and 2500 cm2. As a result, the multiplicity mode was found to be sensitive to the incident neutron angular distribution.
Author: J Harvey Publisher: Elsevier ISBN: 0323146376 Category : Science Languages : en Pages : 549
Book Description
Experimental Neutron Resonance Spectroscopy deals with the experimental technique of neutron resonance spectroscopy. Pulsed accelerator time-of-flight spectrometers and gamma rays from neutron capture in resonances are discussed. Total neutron cross section measurements are presented, along with neutron scattering and capture cross-section measurements and measurements on fissile nuclides. This book is comprised of five chapters and begins with an introduction to pulsed accelerator time-of-flight spectrometers with moderated continued neutron spectra, together with the pulsed Van De Graaff. Experimental techniques used for neutron cross section measurements, including detectors and data acquisition equipment, are then outlined. Scattering measurements and capture measurements as well as gamma-ray spectra from the capture of neutrons in resonances are considered. The final chapter focuses on the detailed and varied experiments that have been performed on the complicated fission process, together with the parameters of the resonances of the fissile nuclides. This monograph will be a useful resource for spectroscopists and physicists.
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: Cyriel Wagemans Publisher: CRC Press ISBN: 9780849354342 Category : Science Languages : en Pages : 636
Book Description
This text provides a comprehensive review of knowledge regarding nuclear fission from both the purely scientific and practical points of view. Topics discussed include fission barriers, spontaneous fission, neutron-induced fission cross-sections, photon- and electron-induced fission, charged particle induced fission fragment angular momentum and ternary fission. The characteristics of other reaction products are also discussed. Contributed articles from several distinguished nuclear scientists guarantee adequate treatment of some of the specialized research fields included in the text. Intended primarily as an introduction to nuclear fission for graduate students, this book will also provide useful information for nuclear physicists involved with research or teaching.
Author: Michael Thomas Nieslony Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) is a 26 ton Gadolinium (Gd)-loaded water Cherenkov detector located on the Booster Neutrino Beam line at Fermilab. Its main goals are the measurement of the neutron multiplicity in neutrino-nucleus interactions as well as the cross-section of Charged Current Quasi-Elastic (CCQE) neutrino interactions on water. Besides the physics goals, the experiment also aims to be a testbed for new technologies such as Large Area Picosecond Photodetectors (LAPPDs) and Water-based Liquid Scintillators (WbLS). This thesis presents a preliminary measurement of the neutron multiplicity with ANNIE}, using an analysis conducted on a fraction of the 2021 beam year. As preparatory measures, the efficiency of ANNIE's Front Muon Veto (FMV) was determined to be $$ bar{ varepsilon}_{ mathrm{FMV}} = (95.6 pm 1.6) %$$} while the average efficiency for active scintillator paddles in the Muon Range Detector (MRD) was found to be $$ bar{ varepsilon}_{ mathrm{MRD}} = (92.1 pm 7.9) %$$}. Furthermore, the simulation framework used for ANNIE was validated and adapted to reproduce the experimental data by comparing the detector response for samples of Michel electrons, Americium Beryllium neutrons, and through-going muons. The analysis finds average neutron yields of $$ bar{n}_{ mathrm{data}} ( mathrmbeam}) = (0.272 pm 0.010_ mathrm{stat}})$$} for an inclusive set of all identified muon neutrino candidates and $$ bar{n}_{ mathrm{data}} ( mathrmbeam,FV}) = (0.287 pm 0.044_ mathrm{stat}})$$ for interactions which happened inside of the Fiducial Volume of ANNIE, which was optimized to increase the neutron detection acceptance. The presented neutron multiplicity values represent the number of detected neutrons after all event selection cuts and are not yet corrected for the neutron detection efficiency. An equivalent analysis on a simulated beam sample predicts neutron yields of $$ barn}_{ mathrm{MC}}( mathrm{beam}) = (0.515 pm 0.007_ mathrm{stat}})$$ and $$ barn}_{ mathrm{MC}}( mathrm{beam,FV}) = (0.627 pm 0.031_ mathrm{stat}})$$, indicating that the models tend to overpredict the number of neutrons produced in such interactions. Systematic errors have been briefly considered to contribute $$ sigma_{ mathrm{sys,FMV}} sim 0.01 ,$$neutrons/$$ nu$$-interaction} due to the slight FMV inefficiency and $$ sigma_{ mathrm{sys,n}} sim 0.05 ,$$neutrons/$$ nu$$-interaction} due to the neutron detection efficiency. Simulation studies further highlighted the importance of neutron detection in Diffuse Supernova Background (DSNB) searches. A combination of neutron tagging and Convolutional Neural Networks was found to reduce the most relevant Neutral Current Quasi-Elastic (NCQE) interaction background below the signal level, achieving a Signal-to-Background ratio of 4:1. In a further study, we investigated the positive impact of a deployment of a WbLS target on the energy reconstruction in ANNIE. WbLS provides a scintillation signal from hadronic recoils in addition to the charged lepton that can be included in neutrino energy reconstruction. It was found that a deployed WbLS volume in ANNIE improves the neutrino energy reconstruction from 14 % to 12 %, with the potential of going beyond this if more sophisticated reconstruction algorithms are developed in the future.
Author: Heejun Chung Publisher: ISBN: Category : Languages : en Pages : 150
Book Description
The nuclear data on the physics of delayed neutrons coming from fission events are of key importance in reactor kinetics and safeguards applications. The accuracy of reactor kinetics calculations, reactor physics validation studies and techniques for non-destructive assay of special nuclear material are all limited by the quality of these data. The uncertainties on the delayed neutron group abundances of the longest-lived delayed neutron groups are particularly large - up to 13 % for thermal fissions of 235U, 16 % for fast fissions of 238U, and 38 % for fast fissions of 239Pu [1]. There are also several competing data sets with significant variation in values. Recent work indicates that these already large uncertainties are underestimated due to numerical instabilities in the parametric fitting methods [2]. A novel approach to experimentally measure delayed neutron group yields has been proposed by Jordan and Perret [3]. This approach combines gamma-ray scanning and delayed neutron fission rate measurement techniques. With two independent estimates of the same fission rate, a higher uncertainty delayed neutron parameters can be linked to lower uncertainty delayed gamma parameters. An experimental apparatus implementing these techniques has been designed, optimized, and built. The apparatus consists of a D-D neutron generator, a detector bundle, a sample handler, and related electronics.
Author: Simon R. Bolding
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Author: 
Author: J Harvey
Author: Thomas Martin
Author: American Nuclear Society
Author: Cyriel Wagemans
Author: Michael Thomas Nieslony
Author: Heejun Chung
Author: Moritz Kütt