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Processing needs and constraints: neutron data processing

Description: New applications for processed data and increased accuracy requirements have generated needs for change in the Evaluated Nuclear Data Files (ENDF). Some constraints must be removed to allow this growth to take place, but other strong constraints must remain to protect existing users.
Date: January 1, 1980
Creator: MacFarlane, R.E.
Partner: UNT Libraries Government Documents Department

Evaluating fission neutron-multiplicity data

Description: The present work had its origins in the practical need to obtain P[sub [nu]] for the purpose of calculating the theoretical response of instrumentation that used a correlation technique to assay spontaneously fissioning nuclides. The assay results are proportional to the factorial moments calculated with the P[sub [nu]] distribution. Obtaining experimentally derived sets of P[sub [nu]] from many sources reported over several decades led immediately to the problem of evaluating the data: Aside from the trivial problem of sometimes not being properly normalized, the first moments ([nu]) = ([nu]) = [Sigma][nu]P[sub [nu]] were typically not in accord with the best recent evaluations, or the calibration of detector efficiency was based on obsolete values for ([nu]) for supposedly well-characterized standard'' nuclides such as [sup 252]Cf. The problem of evaluating P[sub [nu]] is unusual in that, compared to the usual situation where the quantities being evaluated are single numbers, the P[sub [nu]] are sets of numbers, that moreover, are constrained so that [Sigma]P[sub [nu]][triple bond] 1 and [Sigma][nu] P[sub [nu]] = ([nu]), where ([nu]) is usually determined more accurately from a separate experiment than it can be calculated from the experimentally derived P[sub [nu]] distribution.
Date: January 1, 1992
Creator: Zucker, M.S. & Holden, N.E.
Partner: UNT Libraries Government Documents Department

Nuclear physics in the 10 to 300 MeV energy range using a pulsed white neutron source

Description: A new pulsed white neutron source is under construction at the Los Alamos WNR facility. The neutrons are produced by LAMPF proton micropulses striking thick targets of various materials. Beam parameters include energy of 800 MeV, pulse rate of approximately 50,000 Hz, 0.4 nsec pulse width, average current as high as 6..mu..a, and a useful neutron energy range from 3 to 300 MeV. The facility will receive beam approximately 80% of the time LAMPF is operational; it increased by a factor of 1000 the experimental capability over the present system at the WNR when beam intensity, angular distribution, and availability are taken into account. In addition to established white source techniques, the facility is also highly competitive with monoenergetic sources for a wide class of experiments such as neutron capture ..gamma.. ray spectroscopy and neutron-induced charged particle reactions. The facility should be operational in about nine months. Arrangements are underway to make the facility readily accessible to visiting experimenters.
Date: January 1, 1984
Creator: Bowman, C.D.; Wender, S.A. & Auchampaugh, G.F.
Partner: UNT Libraries Government Documents Department

Charge exchange probes of nuclear structure and interactions with emphasis on (p,n)

Description: New results from (p,n) studies at IUCF show that it is possible to observe Gamow-Teller (GT) strength and extract GT matrix elements from (p,n) measurements. The charge exchange reactions (/sup 6/Li,/sup 6/He) and (..pi../sup +/,..pi../sup 0/) involve different projectile quantum numbers, and the relationships of these reactions to (p,n) is discussed.
Date: January 1, 1980
Creator: Goodman, C.D.
Partner: UNT Libraries Government Documents Department

150-m measurement of 0. 880- to 100. 0-keV neutron transmissions through four samples of /sup 238/U

Description: In order to study the /sup 238/U + n total cross section, neutron transmissions through 0.076-, 0.254-, 1.080-, and 3.620-cm-thick samples of isotopically enriched /sup 238/U have been measured from 0.880 to 100.0 keV using a time-of-flight technique over a path length of 150 meters with the ORELA pulsed source and a 13-mm-thick Li-glass detector. The measurement is described in detail and both a listing and figures of the resulting transmissions are given. An absolute energy scale accurate to 2 parts in 10,000 was established.
Date: October 1, 1977
Creator: Olsen, D. K.; de Saussure, G.; Perez, R. B.; Difilippo, F. C.; Ingle, R. W. & Weaver, H.
Partner: UNT Libraries Government Documents Department

Analysis of neutron data in the resonance region via the computer code SAMMY

Description: Procedures for analysis of resonance neutron cross-section data have been implemented in a state-of-the-art computer code SAMMY, developed at the Oak Ridge Electron Linear Accelerator (ORELA) at Oak Ridge National Laboratory. A unique feature of SAMMY is the use of Bayes' equations to determine ''best'' values of parameters, which permits sequential analysis of data sets (or subsets) while giving the same results as would be given by a simultaneous analysis. Another important feature is the inclusion of data-reduction parameters in the fitting procedure. Other features of SAMMY are also described.
Date: January 1, 1985
Creator: Larson, N.M.
Partner: UNT Libraries Government Documents Department

Consistency of differential and integral thermonuclear neutronics data

Description: To increase the accuracy of the neutronics analysis of nuclear reactors, physicists and engineers have employed a variety of techniques, including the adjustment of multigroup differential data to improve consistency with integral data. Of the various adjustment strategies, a generalized least-squares procedure which adjusts the combined differential and integral data can significantly improve the accuracy of neutronics calculations compared to calculations employing only differential data. This investigation analyzes 14 MeV neutron-driven integral experiments, using a more extensively developed methodology and a newly developed computer code, to extend the domain of adjustment from the energy range of fission reactors to the energy range of fusion reactors.
Date: January 1, 1978
Creator: Reupke, W.A.
Partner: UNT Libraries Government Documents Department

Use of R-matrix methods for light element evaluations

Description: Some general aspects of parameterizing nuclear reaction data with a unitary, multichannel theory are discussed. The special case of R-matrix theory are discussed. The special case of R-matrix theory is considered, where the explicit separation of long- and short-range forces and the natural occurrence of energy pole terms afford a number of advantages in describing data for light-element reactions. Examples are given for both neutron- and charged-particle-induced reactions which illustrate multichannel R-matrix techniques, including the use of charge symmetry to relate data for mirror systems. The limitations of conventional R-matrix methods are discussed briefly.
Date: January 1, 1980
Creator: Hale, G.M.
Partner: UNT Libraries Government Documents Department

Nuclear data and related services

Description: National Nuclear Data Center (NNDC) maintains a number of data bases containing bibliographic information and evaluated as well as experimental nuclear properties. An evaluated computer file maintained by the NNDC, called the Evaluated Nuclear Structure Data File (ENSDF), contains nuclear structure information for all known nuclides. The ENSDF is the source for the journal ''Nuclear Data Sheets'' which is produced and edited by NNDC. The Evaluated Nuclear Data File (ENDF), on the other hand is designed for storage and retrieval of such evaluated nuclear data as are used in neutronic, photonic, and decay heat calculations in a large variety of applications. Some of the publications from these data bases are the Nuclear Wallet Cards, Radioactivity Handbook, and books on neutron cross sections and resonance parameters. In addition, the NNDC maintains three bibliographic files: NSR - for nuclear structure and decay data related references, CINDA - a bibliographic file for neutron induced reactions, and CPBIB - for charged particle reactions. Selected retrievals from evaluated data and bibliographic files are possible on-line or on request from NNDC. 6 refs., 1 fig.
Date: January 1, 1985
Creator: Tuli, J.K.
Partner: UNT Libraries Government Documents Department

Energy-averaged neutron cross sections of fast-reactor structural materials

Description: The status of energy-averaged cross sections of fast-reactor structural materials is outlined with emphasis on U.S. data programs in the neutron-energy range 1-10 MeV. Areas of outstanding accomplishment and significant uncertainty are noted with recommendations for future efforts. Attention is primarily given to the main constituents of stainless steel (e.g., Fe, Ni, and Cr) and, secondarily, to alternate structural materials (e.g., V, Ti, Nb, Mo, Zr). Generally, the mass regions of interest are A approximately 50 to 60 and A approximately 90 to 100. Neutron total and elastic-scattering cross sections are discussed with the implication on the non-elastic-cross sections. Cross sections governing discrete-inelastic-neutron-energy transfers are examined in detail. Cross sections for the reactions (n;p), (n;n',p), (n;..cap alpha..), (n;n',..cap alpha..) and (n;2n') are reviewed in the context of fast-reactor performance and/or diagnostics. The primary orientation of the discussion is experimental with some additional attention to the applications of theory, the problems of evaluation and the data sensitivity of representative fast-reactor systems.
Date: February 1, 1978
Creator: Smith, A.; McKnight, R. & Smith, D.
Partner: UNT Libraries Government Documents Department

Present status of laser driven fusion--fission energy systems

Description: The potential of laser fusion driven hybrids to produce fissile fuel and/or electricity has been investigated in the laser program at the Lawrence Livermore Laboratory (LLL) for several years. Our earlier studies used neutronic methods of analysis to estimate hybrid performance. The results were encouraging, but it was apparent that a more accurate assessment of the hybrid's potential would require studies which treat the engineering, environmental, and economic issues as well as the neutronic aspects. More recently, we have collaborated with Bechtel and Westinghouse Corporations in two engineering design studies of laser fusion driven hybrid power plants. With Bechtel, we have been engaged in a joint effort to design a laser fusion driven hybrid which emphasizes fissile fuel production while the primary objective of our joint effort with Westinghouse has been to design a hybrid which emphasizes power production. The hybrid designs which have resulted from these two studies are briefly described and analyzed by considering their most important operational parameters.
Date: May 1, 1978
Creator: Maniscalco, J.A. & Hansen, L.F.
Partner: UNT Libraries Government Documents Department

Analysis of the /sup 235/U neutron cross sections in the resolved resonance range

Description: Using recent high-resolution measurements of the neutron transmission of /sup 235/U and the spin-separated fission cross-section data of Moore et al., a multilevel analysis of the /sup 235/U neutron cross sections was performed up to 300 eV. The Dyson Metha ..delta../sub 3/ statistics were used to help locate small levels above 100 eV where resonances are not clearly resolved even in the best resolution measurements available. The statistical properties of the resonance parameters are discussed. 13 refs., 8 figs., 1 tab.
Date: January 1, 1989
Creator: Leal, L.C.; de Saussure, G. & Perez, R.B.
Partner: UNT Libraries Government Documents Department

Fission cross section ratios for sup 233,234,236 U relative to sup 235 U from 0. 5 to 400 MeV

Description: Neutron-induced fission cross section ratios from 0.5 to 400 MeV for samples of {sup 233, 234, 236}U relative to {sup 235}U have been measured at the WNR neutron Source at Los Alamos. The fission reaction rate was determined using a fast parallel plate ionization chamber at a 20-m flight path. Cross sections over most the energy range were also extracted using the neutron fluence determined with three different proton telescope arrangements. Those data provided the shape of the {sup 235}U(n,f) cross section relative to the hydrogen scattering cross section. That shape was then normalized to the very accurately known value for {sup 235}U(n,f) at 14.1 MeV to allow us to obtain cross section section values from the ratio data and our values for {sup 235}U(n,f). 6 refs., 1 fig.
Date: January 1, 1991
Creator: Lisowski, P.W.; Gavron, A.; Parker, W.E.; Balestrini, S.J. (Los Alamos National Lab., NM (USA)); Carlson, A.D.; Wasson, O.A. (National Inst. of Standards and Technology, Gaithersburg, MD (USA)) et al.
Partner: UNT Libraries Government Documents Department

Perspective on occupational radiation exposures at a hypothetical fusion power station

Description: If current technology were used, several major sources of potential occupational radiation exposure at fusion power stations would be quite similar to those at current light water reactor power stations. Based upon this similarity, crude estimates of doses received from various maintenance operations at fusion power reactors are made. The dose estimates reinforce the need for concurrent development of sophisticated remote maintenance devices and low-activation materials for fusion reactors. It is concluded that minimization of occupational doses can be best achieved by developing an overall maintenance strategy that combines the best features of remote techniques and low activation materials as opposed to developing one or the other exclusively.
Date: January 1, 1983
Creator: Easterly, C.E. & Cannon, J.B.
Partner: UNT Libraries Government Documents Department

Advanced nuclear data for radiation-damage calculations

Description: Accurate calculations of atomic displacement damage in materials exposed to neutrons require detailed spectra for primary recoil nuclei. Such data are not available from direct experimental measurements. Moreover, they cannot always be computed accurately starting from evaluated nuclear data libraries such as ENDF/B-V that were developed primarily for neutron transport applications, because these libraries lack detailed energy-and-angle distributions for outgoing charged particles. Fortunately, a new generation of nuclear model codes is now available that can be used to fill in the missing spectra. One example is the preequilibrium statistical-model code GNASH. For heating and damage applications, a supplementary code called RECOIL has been developed. RECOIL uses detailed reaction data from GNASH, together with angular distributions based on Kalbach-Mann systematics to compute the energy and angle distributions of recoil nuclei. The energy-angle distributions for recoil nuclei and outgoing particles are written out in the new ENDF/B File 6 format. The result is a complete set of nuclear data that can be used to calculate displacement-energy production, heat production, gas production, transmutation, and activation. Sample results for iron are given and compared to the results of conventional damage models such as those used in NJOY.
Date: January 1, 1983
Creator: MacFarlane, R.E. & Foster, D.G. Jr.
Partner: UNT Libraries Government Documents Department

Generation of broad-group neutron/photon cross-section libraries for shielding applications

Description: The generation and use of multigroup cross-section libraries with broad energy group structures is primarily for the economy of computer resources. Also, the establishment of reference broad-group libraries is desirable in order to avoid duplication of effort, both in terms of the data generation and verification, and to assure a common data base for all participants in a specific project. Uncertainties are inevitably introduced into the broad-group cross sections due to approximations in the grouping procedure. The dominant uncertainty is generally with regard to the energy weighting function used to average the pointwise or fine-group data within a single broad group. Intelligent choice of the weighting functions can reduce such uncertainties. Also, judicious selection of the energy group structure can help to reduce the sensitivity of the computed responses to the weighting function, at least for a selected set of problems. Two new multigroup cross section libraries have been recently generated from ENDF/B-V data for two specific shielding applications. The first library was prepared for use in sodium-cooled reactor systems and is available in both broad-group structures. The second library, just recently completed, was prepared for use in air-over-ground environments and is available in a broad-group (46-neutron, 23-photon) energy structure. The selection of the specific group structures and weighting functions was an important part of the generation of both libraries.
Date: January 1, 1989
Creator: Ingersoll, D.T.; Roussin, R.W.; Fu, C.Y. & White, J.E.
Partner: UNT Libraries Government Documents Department

Fusion applications of copper: unique requirements in resistive magnets

Description: The Fusion Engineering Design Center (FEDC) is focusing FY 1983 activities on evaluating upgrade alternatives for the major fusion device now being completed. FEDC resources are divided equally betweek tokamak applications, in support of TFTR upgrade, and tandem mirror applications, supporting upgrade of the MFTF-B facility. In the course of magnet system design studies related to these activities, several needs for water cooled copper coils are presently perceived. The applications discussed in this paper are the high field choke coils (tandem mirror) and toroidal field coils or coil inserts (tokamaks). In these applications, the important properties are low electrical resistance, high mechanical strength and tolerance to neutron fluence.
Date: January 1, 1983
Creator: Hunter, B.
Partner: UNT Libraries Government Documents Department

Key changes in nuclear data in the transition from ENDF/B-V to ENDF/B- VI

Description: Major changes were made in the evaluated nuclear data base in going from ENDF/B-V to ENDF/B-VI. A complete revision of all the cross sections standards was implemented using results from a simultaneous analysis of all standard reactions; energy-angle correlated secondary distributions for emitted particles and gamma rays were introduced; many natural element evaluations were replaced by isotopic data; vastly expanded fission-product yield and decay data files were included; and altogether some 74 general purpose data evaluations were either completely replaced or significantly revised. Applications that will utilize nuclear data from the recently issued ENDF/B-VI library are varied in scope, and a number of the improvements and changes that have occurred relative to the previous library are significant for certain of the application areas. The purpose of this paper is to examine the changes in data that have occurred in a selection of nuclear reactions important for applications, emphasizing several that influence results in key data testing calculations. In particular, the paper highlights revisions in neutron-induced reactions from {sup 14}N and {sup 16}O that are important in calculating neutron transport and/or reflection in air, and some of the changes in data for {sup 235}U, {sup 238}U, and {sup 239}Pu that are significant in fast reactor applications.
Date: January 1, 1991
Creator: Young, P.G.
Partner: UNT Libraries Government Documents Department

Neutron-induced angular and energy distributions: graphical experimental data

Description: Graphs of neutron-induced distributions have been generated, based on the data found in the Experimental Cross Section Information Library (ECSIL) as of April 1, 1977. Angular and energy distributions as well as Legendre coefficients have been presented for all secondary particles emitted from the nucleus (e.g., neutrons, protons, deuterons, etc.). The data have been plotted with error bars when they have been available.
Date: April 1, 1977
Creator: Cullen, D.E.; Howerton, R.J.; MacGregor, M.H. & Perkins, S.T.
Partner: UNT Libraries Government Documents Department

Neutron-photon multigroup cross sections for neutron energies less than or equal to400 MeV. Revision 1

Description: For a variety of applications, e.g., accelerator shielding design, neutrons in radiotherapy, radiation damage studies, etc., it is necessary to carry out transport calculations involving medium-energy (greater than or equal to20 MeV) neutrons. A previous paper described neutron-photon multigroup cross sections in the ANISN format for neutrons from thermal to 400 MeV. In the present paper the cross-section data presented previously have been revised to make them agree with available experimental data. 7 refs., 1 fig.
Date: January 1, 1986
Creator: Alsmiller, R.G. Jr.; Barnes, J.M. & Drischler, J.D.
Partner: UNT Libraries Government Documents Department

Preliminary measurement of the /sup 235/U(n,f) cross section up to 750 MeV

Description: The recently commissioned high energy white neutron source was used to measure the neutron fission cross section of /sup 235/U in the energy range from 0.6 to 750 MeV. The shape of the cross section from 0.6 to 20 MeV agrees well with previous reported data. Absolute values for the /sup 235/U(n,f) cross section from 20 MeV to 750 MeV were obtained by normalizing the measured shape of the cross section to data in the 10 to 20 MeV range. 12 refs., 9 figs.
Date: October 1, 1987
Creator: Rapaport, J.; Ullmann, J.; Nelson, R.O.; Seestrom-Morris, S.; Wender, S.A. & Haight, R.C.
Partner: UNT Libraries Government Documents Department