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Leakage Neutron Spectrum of U²³³ Critical Assembly

Description: Abstract: "The leakage neutron spectrum of a U²³³ spherical critical assembly (Jezebel) has been measured using nuclear emulsions as radiator and detector. The spectrum obtained is compared with similar measurements on the U-235 and Pu-239 analogues of Jezebel U²³³; it is found to agree closely with that of the Pu-239 assembly and to be harder than that of the U-235 assembly. All three spectra are compared with theoretical spectra obtained from a numerical approximation to the neutron transport equation."
Date: September 1962
Creator: Bobisud, Larry E.
Partner: UNT Libraries Government Documents Department

Co-adsorption studies of hydrogen with nitrogen in zeolites

Description: The use of co-adsorption studies of N{sub 2} with H{sub 2} makes it possible to obtain information about adsorption of N{sub 2} by monitoring changes in the rotational spectrum of the co-adsorbed H{sub 2} molecules. The authors present such results on N{sub 2}/H{sub 2} in Na-13X. The authors have demonstrated that inelastic neutron scattering studies of H{sub 2} co-adsorbed with other molecules can be used as an effective probe of their adsorption sites and interactions with zeolite hosts. Simulation studies are clearly required for extracting the wealth of detail which is evident in these data.
Date: August 1998
Creator: Eckert, J.; Trouw, F. R. & McMenomy, M.
Partner: UNT Libraries Government Documents Department

Simultaneous neutron and gamma spectrum adjustment

Description: The spectrum adjustment procedure was extended to simultaneous neutron and gamma spectrum adjustment, and the feasibility of this technique is demonstrated in the analysis of HFIR dosimetry experiments. Conditions in which gamma rays may contribute considerably to radiation damage in steels are discussed. Beryllium helium accumulation fluence monitors (HAFMs) were found to be good monitors in gamma fields of intensities high enough to contribute to steel embrittlement. Use of {sup 237}Np, {sup 238}U, and {sup 9}Be HAFM as gamma dosimeters is proposed for high-dose irradiations in high-energy, high-intensity gamma fields.
Date: October 1, 1996
Creator: Remec, I.
Partner: UNT Libraries Government Documents Department

Shielding materials for high-energy neutrons

Description: The authors used the Monte Carlo transport code Los Alamos High-Energy Transport (LAHET) to study the shielding effectiveness of common shielding materials for high-energy neutrons. The source neutron spectrum was from the interaction of an 800-MeV proton beam and iron target. In a normal incident, the neutrons collided with walls made of six common shielding materials: water, concrete, iron, lead, polyethylene, and soil. The walls were of four different thicknesses: 25, 50, 75 and 100 cm. They then tallied the neutron spectra on the other side of the shielding wall and calculated the neutron doses. For the high-Z materials--iron and lead--they find that many neutrons with energies between 1--10 MeV are created when high-energy neutrons interact with shielding materials. For materials containing low-Z elements--water, soil, concrete, and polyethylene--the spectra show higher energy peaks at about 100 MeV. The studies show that for a given wall thickness, concrete is more effective than the other materials. They also studied the effectiveness of combinations of materials, such as concrete and water, concrete and soil, iron and polyethylene, or iron polyethylene and concrete.
Date: May 1, 1997
Creator: Hsu, H.H.
Partner: UNT Libraries Government Documents Department

Vibrational dynamics of crystalline L-alanine

Description: The authors report a new, complete vibrational analysis of L-alanine and L-alanine-d{sub 4} which utilizes IINS intensities in addition to frequency information. The use of both isotopomers resulted in a self-consistent force field for and assignment of the molecular vibrations in L-alanine. Some details of the calculation as well as a comparison of calculated and observed IINS spectra are presented. The study clarifies a number of important issues on the vibrational dynamics of this molecule and presents a self-consistent force field for the molecular vibrations in crystalline L-alanine.
Date: November 1, 1997
Creator: Bordallo, H.N.; Eckert, J. & Barthes, M.
Partner: UNT Libraries Government Documents Department

New Monte Carlo simulations of the LLNL pulsed-sphere experiments

Description: From the late 1960s to about 1985, the Pulsed-Sphere Program at Lawrence Livermore National Laboratory (LLNL) was carried out to measure 14-MeV neutron leakage spectra from target spheres made out of various elements, compounds, and mixtures Data from these experiments have been and continue to be fundamental in the evaluation of neutron Monte Carlo transport codes and cross section data libraries In addition, the data provide important integral information for stockpile stewardship, fusion technology, neutron therapy, and other applications Therefore, comparisons between computer Monte Carlo simulations and the results of these experiments are pivotal for the integral testing of processed nuclear data libraries and transport codes Fortunately, a large subset of data from the pulsed-sphere program (some 70 experiments) is available as a computer file called disp93in Furthermore, in the past few years, there has been a remarkable improvement in computer performance that allows for more realistic simulations by Monte Carlo codes such as TART 4 Previous TART simulations of the pulsed-sphere experiments were performed using simplified models with relatively small numbers of histories and very large solid angle detectors to offset the limitations in computer power. Also, not all the TART input files were created with the same level of detail For example, some input files included the air around the sphere while others did not These factors prompted a study to simulate in more detail all of the available pulsed-sphere experiments using the Monte Carlo transport code, TART, and the LLNL evaluated neutron data library, ENDL The timing of this study is significant because many years have passed since those experiments were done, and only a few people who participated in them are still working at LLNL Their help has been essential for an accurate documentation of the experiments For the Stewardship Program it is important to preserve ...
Date: July 1, 1998
Creator: Marchetti, A.A., LLNL
Partner: UNT Libraries Government Documents Department

Influence of Neutron Energy Spectrum on Primary Damage Formation

Description: Displacement cascade formation in iron has been investigated by the method of molecular dynamics (MD) for cascade energies up to 40 keV. The results of these simulations have been used to obtain effective, energy-dependent cross sections for two measures of primary damage production: (1) the number of surviving point defects expressed as a fraction of the those predicted by the standard secondary displacement model by Norgett, Robinson, and Torrens (NRT),and (2) the fraction of the surviving interstitials contained in clusters that formed during the cascade event. The primary knockon atom spectra for iron obtained from the SPECTER code have been used to weight these MD-based damage production cross sections in order to obtain spectrally-averaged values for several locations in commercial fission reactors, materials test reactors, a DT fusion reactor first wall, and a pulsed spallation neutron source. An evaluation of these results indicates that neutron energy spectrum differences between the various environments do not lead to significant differences between the average primary damage formation parameters. This conclusion implies that the displacement damage component of radiation damage produced in a high energy spallation neutron source should be well simulated by irradiation in a fission reactor neutron spectrum, and that differences in nuclear transmutation production may be a greater source of uncertainty in the prediction of material performance in the planned National Spallation Neutron Source.
Date: December 31, 1997
Creator: Stoller, R. E.
Partner: UNT Libraries Government Documents Department

Theory of neutron emission in fission

Description: A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and some examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated in detail for the Los Alamos model. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of the ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. This paper is an extension of a similar paper presented at the International Centre for Theoretical Physics in 1996.
Date: August 1998
Creator: Madland, D. G.
Partner: UNT Libraries Government Documents Department

Post-scission fission theory: Neutron emission in fission

Description: A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N (E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N (E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N (E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches.
Date: November 1, 1997
Creator: Madland, D. G.
Partner: UNT Libraries Government Documents Department

Predicted performance of neutron spectrometers using scintillating fibers

Description: A variety of needs exists for knowing the energy spectral content of a neutron flux. Among these needs are arms-control and national-security applications, which arise because different neutron sources produce different neutron energy spectra. This work is primarily directed at these applications. The concept described herein is a spectrometer in the same sense as a Bonner sphere. The instrument response reflects a statistical average of the energy spectrum. The Bonner sphere is an early rendition of this class. In this, a neutron detector is placed at the center of a moderating (and absorbing) sphere (of varying thickness and composition). Spectral unfolding is required, and the resolution and efficiency are, typically, poor, although the potential bandwidth is very large. A recent variation on the Bonner-sphere approach uses {sup 3}He gas proportional counters with resistive wires to locate the position of the event (Toyokawa et al 1996). The spectrometer concept investigated here has the potential for better resolution and much improved neutron efficiency compared to Bonner spheres and similar devices. These improvements are possible because of the development of neutron-sensitive, scintillating-glass fibers. These fibers can be precisely located in space, which allows a corresponding precision in energy resolution. Also, they can be fabricated into arrays that intercept a large fraction of incident thermal neutrons, providing the improvement in neutron economy.
Date: February 14, 2000
Creator: Craig, RA & Bliss, M
Partner: UNT Libraries Government Documents Department

Experiment proposal for the determination of neutron spectra from targeted electron beams

Description: There is a dearth of experimental data on the production and yields of neutrons from targeted electron beams; yet, for accelerator radiation protection these data are of the greatest importance in setting up methods of shielding and other means for protecting people against ionizing radiation. Although adequate for simple cases and lateral production angles, empirical analytical methods are not suitable for the more complicated geometries or source configurations often met with in practice. Monte Carlo (MC) methods that model the transport of neutrons provide far better results in many cases but rely on the random generation of the energy of a source particle selected for any beam condition, production angle and target configuration. A number of theoretical approaches to the derivation of a model for the production of particle events at energies greater than the giant resonance region have been made. Many of these are based on the quasi deuteron model of the nucleus and operate over photon energies in the range 30 MeV to 400 MeV. A method is also available, based on the vector meson dominance model which is designed to work above the photopion resonance region where the cross section levels off at a few GeV (Ranft 1987). Both of these models are limited in utility to a certain energy range and both show some discrepancies with existing empirical methods. More recently a new fragmentation model was developed, which could be used over a large energy range and modeled all production processes. This new method also showed differences from the traditional approaches and a thorough comparison indicated that the event generator in conjunction with conventional MC transport codes produced results a factor two to three higher than the results using the empirical methods. This unsatisfactory situation can only be resolved by making measurements of proper physical quantities ...
Date: October 1, 1996
Creator: Degtyarenko, P. & Stapleton, G.
Partner: UNT Libraries Government Documents Department

Interlaboratory Neutron Flux Spectral Measurement Program

Description: This report details an interlaboratory cooperative study undertaken on neutron flux spectral measurements, calculations, and data correlation for reactor irradiation and physics study by various sites. The Testing portion of this study was the irradiation of a wide variety of flux monitors in a special snout capsule holder. The attached sketch shows the capsule holder design, facility design, and the capsule position in relation to adjacent process tubes. A summary of the irradiations performed is provided.
Date: March 7, 1966
Creator: DeMers, A.E.
Partner: UNT Libraries Government Documents Department

Neutron Contribution to CaF2:Mn Thermoluminescent Dosimeter Response in Mixed (n/y) Field Environments

Description: Thermoluminescent dosimeters (TLDs), particularly CaF{sub 2}:Mn, are often used as photon dosimeters in mixed (n/{gamma}) field environments. In these mixed field environments, it is desirable to separate the photon response of a dosimeter from the neutron response. For passive dosimeters that measure an integral response, such as TLDs, the separation of the two components must be performed by post-experiment analysis because the TLD reading system cannot distinguish between photon and neutron produced response. Using a model of an aluminum-equilibrated TLD-400 chip, a systematic effort has been made to analytically determine the various components that contribute to the neutron response of a TLD reading. The calculations were performed for five measured reactor neutron spectra and one theoretical thermal neutron spectrum. The five measured reactor spectra all have dosimetry quality experimental values for aluminum-equilibrated TLD-400 chips. Calculations were used to determined the percentage of the total TLD response produced by neutron interactions in the TLD and aluminum equilibrator. These calculations will aid the Sandia National Laboratories-Radiation Metrology Laboratory (SNL-RML) in the interpretation of the uncertainty for TLD dosimetry measurements in the mixed field environments produced by SNL reactor facilities.
Date: November 1, 2002
Creator: DEPRIEST, KENDALL R.
Partner: UNT Libraries Government Documents Department

DEVELOPMENT AND VALIDATION OF THE 7LI(P,N) NUCLEAR DATA LIBRARY AND ITS APPLICATION IN MONITORING OF INTERMEDIATE ENERGY NEUTRONS

Description: Systematics have been created for neutron spectra from the 7Li(p,n) reaction at 0 degrees in the 50-200 MeV proton energy region. The available experimental data in the continuum part of the spectra show satisfactory overall agreement with a representation based on the phase-space distribution corresponding to the three-body breakup process 7Li(p,n 3He){alpha}, with empirical correction factors, which depend regularly on incident energy. Validation of the systematics included folding of the predicted neutron spectra with standard 238U neutron fission cross section. Modeled in this way distributions of neutron-induced fission events agree reasonably with experimental data. KEYWORDS: quasi-monoenergetic neutron beam, monitoring, nuclear data library, MCNPX code.
Date: January 1, 2001
Creator: Mashnik, S. G. (Stepan G.); Chadwick, M. B. (Mark B.); Prokofiev, A. (Alexander); Olsson, N. (Nils) & Waters, L. S. (Laurie S.)
Partner: UNT Libraries Government Documents Department

Development and Validation of Temperature Dependent Thermal Neutron Scattering Laws for Applications and Safety Implications in Generation IV Reactor Designs

Description: The overall obljectives of this project are to critically review the currently used thermal neutron scattering laws for various moderators as a function of temperature, select as well documented and representative set of experimental data sensitive to the neutron spectra to generate a data base of benchmarks, update models and models parameters by introducing new developments in thermalization theory and condensed matter physics into various computational approaches in establishing the scattering laws, benchmark the results against the experimentatl set. In the case of graphite, a validation experiment is performed by observing nutron slowing down as a function of temperatures equal to or greater than room temperature.
Date: June 20, 2008
Creator: Hawari, Ayman
Partner: UNT Libraries Government Documents Department

Lawrence Livermore Laboratory Evaluated Nuclear Data Library (ENDL) translated into the ENDF/B format

Description: The LLL Evaluated Nuclear Data Library (ENDL) was translated into the ENDF/B Format. This translation is for the convenience of those people who wish to use the ENDL data, but whose main familiarity is with the ENDF/B formats and procedures. Only the portion of ENDL which deals with neutioninduced interactions (including photon production from neutroninduced reactions) was translated. Those parts of the ENDL library which deal with charged-particle- induced reactions were not translated, since they cannot be accommodated within the ENDF/B system. In order to provide a basis ior judging the validity of the ENDL data calculations were made of the output neutron time spectra from the LLL pulsed-sphere experiments, by using for the calculations both the ENDL cross sections and the ENDF/B-III cross sections. Comparisons between these two sets of calculations and the experimental output neutron time spectra provide a basis for judging the relative merits of the ENDL and ENDF-/B-III data sets in the 5 to 20 MeV neutronenergy regime. (auth)
Date: October 1, 1973
Creator: Howerton, R. J.
Partner: UNT Libraries Government Documents Department