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A-dependence of nuclear transparency in quasielastic A(e,e{prime}p) at high Q{sup 2}

Description: The A-dependence of the quasielastic A(e,e{prime}p) reaction has been studied with {sup 3}H, C, Fe, and Au nuclei at momentum transfers Q{sup 2} = 1, 3, 5, and 6.8(GeV/c){sup 2}. The authors extract the nuclear transparency T(A,Q{sup 2}), a measure of the average probability of escape of a proton from a nucleus A. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as color transparency. No statistically significant rise is seen for any of the nuclei studied.
Date: May 1, 1994
Creator: O`Neill, T.G.; Lorenzon, W. & Arrington, J.
Partner: UNT Libraries Government Documents Department

Quasi-free ({ital e,e`p}) reactions: the first look from CEBAF

Description: Coincidence cross sections for ({ital e,e{sup `}p}) quasi-elastic scattering were measured at CEBAF with high statistical precision for C, Fe, and Au targets for 0.6 {lt} Q{sup 2} {lt} 3.3 GeV{sup 2}. {ital E{sub m}} and {ital P{sub m}} distributions obtained from a preliminary analysis are in reasonable agreement with prior data from SLAC, The preliminary results are compared with a PWIA calculation to determine the nuclear transparency as a function of Q{sup 2} and A. A. Rosenbluth analysis to extract the longitudinal and transverse cross sections from these data is anticipated.
Date: November 1, 1996
Creator: Abbott, D.; Amatuoni, T. & Armstrong, C.
Partner: UNT Libraries Government Documents Department

Precision Measurements of {sup 56}Fe Cross Sections for the 847-keV Gamma Transition

Description: At the First Research Coordination Meeting of the IAEA/NDS CRP on Measurement, Calculation and Evaluation of Photon Production Data an experiment to measure with high precision the cross sections of the production of the 847-keV gamma ray due to inelastic neutron scattering with iron was proposed and discussed. The main justification for the proposed improved precision was the need for improved calculations of radiation transport through thick iron components of nuclear reactors. Present evaluated data for the subject reaction in the ENDF/B-VI files have evaluated uncertainties {approx} 10%; consequently, the results of computation of deep penetration of radiation in iron can have quite large uncertainties -- larger than 100%, for example, for an attenuation of {approximately} three orders of magnitude -- which can be a serious problem when one considers the magnitude of the radiation field inside a pressure vessel. This report describes progress toward obtaining more precise data. 13 refs., 1 fig.
Date: December 31, 1997
Creator: Dickens, J.K.
Partner: UNT Libraries Government Documents Department

Momentum transfer dependence of medium effects in the (e,e{prime}) longitudinal response

Description: Recent {sup 56}Fe(e,e{prime}) data at momentum transfer {vert_bar}{bar q}{vert_bar} = 1.14 GeV displays behavior which is qualitatively different from that of lower momentum transfers. An explanation of this difference is offered based on an analysis of the longitudinal response in nuclear matter. An ansatz is made for the momentum dependence of the nucleon self-energy functions in the nuclear medium which suppresses medium effects for momenta above the nucleon mass scale. This suppression is shown to improve the agreement with the high momentum transfer region between 0.5 and 1.0 GeV.
Date: April 1, 1994
Creator: Frank, M. R.
Partner: UNT Libraries Government Documents Department

Experimental results of neutron fluence outside an iron shield in the forward direction

Description: Analyses of both lateral shielding measurements and Monte Carlo calculations for beam stop geometry for incident hadrons at energies between 10 GeV and 10 TeV suggests that the dose equivalent can be represented by the expression H = H{sub 0}(E)e{sup -r/{lambda}}/r{sup 2} where H, is the source term, r is the radial distance to the point of interest in the shield, and {lambda} is the effective interaction length, or absorption mean free path. However, unlike the lateral shielding case, there is no similarly simple analytical expression that can be used to describe the on-axis longitudinal cascade development. In this study the results from the measurement in the forward direction of neutron fluence spectra (and the derived quantity dose equivalent) for 25 to 150 GeV pions incident on an iron beam stop as a function of thickness of iron are presented. The observed dependence of both fluence and dose equivalent on shield thickness and hadron energy was then quantified in terms of an expression in which a build up factor as well as an attenuation term was included. On the basis of this analysis the conversion factor from fluence to dose equivalent was also determined for these forward going neutrons. This work represents the first systematic study at an high energy accelerator of the depth dependence of neutron fluence in longitudinal shielding.
Date: September 1, 1996
Creator: Torres, M.M.C.; Elwyn, A.J.; Fein, D.; James, E.; Johns, K.; Davis, W. et al.
Partner: UNT Libraries Government Documents Department

Assessment of some optical model potentials in predicting neutron cross sections

Description: Optical model potential parameters play an important role in the evaluation of nuclear data for applied purposes. The IAEA Coordinated Research Program on {open_quotes}Reference Input Parameter Library for Evaluation of Nuclear Data for Application in Nuclear Technology{close_quotes} aims to release a reference input file of various types of parameters for the evaluation of nuclear cross sections using nuclear model codes. Included in the parameter files are a collection of optical model potentials that are available in the literature to evaluate these cross sections. As part of this research program we assess the applicability of these potentials over a range of target mass and projectile energy.
Date: March 1, 1998
Creator: Kumar, A.; Young, P.G. & Chadwick, M.B.
Partner: UNT Libraries Government Documents Department

Charged particles produced in neutron reactions on nuclei from beryllium to gold

Description: Charged-particle production in reactions of neutrons with nuclei has been studied over the past several years with the spallation source of neutrons from 1 to 50 MeV at the Los Alamos Neutron Science Center (LANSCE). Target nuclides include 9Be, C, 27Al, Si, 56Fe, 59Co, 58,60Ni, 93Nb and 197Au. Proton, deuteron, triton, 3He and 4He emission spectra, angular distributions and production cross sections have been measured. Transitions from the compound nuclear reaction mechanism to precompound reactions are clearly seen in the data. The data are compared with data from the literature where available, with evaluated nuclear data libraries, and with calculations where the selection of the nuclear level density prescription is of great importance. Calculations normalized at En = 14 MeV can differ from the present data by a factor of 2 for neutron energies between 5 and 10 MeV.
Date: August 1, 1997
Creator: Haight, R.C.
Partner: UNT Libraries Government Documents Department

Status of optical model activities at Los Alamos National Laboratory

Description: An update will be given of activities at Los Alamos National Laboratory aimed at developing optical model potentials for applied calculations. Recent work on a coupled-channels potential for neutron reactions on {sup 241,243}Am and spherical neutron potential updates for {sup 56}Fe and {sup 59}Co will be presented, together with examples of their application in nuclear reaction calculations with the GNASH code system. New potentials utilized in evaluations at Livermore for {sup 12}C, {sup 14}N and {sup 16}O are described and additional potentials from earlier analyses at Los Alamos of Ti, V, and Ni data are made available for possible inclusion in the Reference Input Parameter Library (RIPL) for nuclear model calculations of nuclear data. Specific activities directed at development of the optical potential segment of the RIPL will be summarized.
Date: December 1, 1995
Creator: Young, P.G.
Partner: UNT Libraries Government Documents Department

Much ado about nothing: deep minima in /sup 45/Sc and /sup 56/Fe total neutron cross sections

Description: The deep minima in /sup 45/Sc and /sup 56/Fe neutron total cross sections were measured at the Gaerttner Linac Laboratory by using thick, ultra-pure samples in transmission experiments. The samples are used to produce quasi-monoenergetic beams at the BNL High Flux Beam Reactor. For the /sup 45/Sc minimum near 2.05 keV we obtain sigma/sub total/ = 0.71 +- 0.03 barns, in sharp contrast to a previously reported value of approximately 0.05 barns. The /sup 56/Fe measurement was carried out with a 6 kg, 68.58-cm-long sample of 99.87% isotopically pure sample of /sup 56/Fe; a minimum cross section of 0.0085 +- 0.004 barns at 24.39 keV is inferred. This may be compared to a value of 0.420 barns for natural iron.
Date: January 1, 1977
Creator: Chrien, R.E.; Liou, H.I.; Block, R.C.; Singh, U.N. & Kobayashi, K.
Partner: UNT Libraries Government Documents Department

The {sup 56}Fe(n,x {alpha}) reaction from threshold to 30 MeV

Description: Alpha-particle emission in neutron reactions with {sup 56}Fe has been studied from threshold to over 30 MeV using the spallation neutron source at WNR/LAMPF. Alpha-particle production cross sections, spectra, and angular distributions were measured at scattering angles of 30, 60, 90, and 135 degrees using detector telescopes consisting of a low-pressure gas proportional counter and a large area silicon detector. Time-of-flight techniques with a 10-meter flight path were used to deduce the incident neutron energies. Our results are compared with literature values and with several theoretical calculations.
Date: June 1, 1994
Creator: Sterbenz, S. M.; Young, P. G. & Bateman, F. B.
Partner: UNT Libraries Government Documents Department

Analysis of Fe(n,x{gamma}) cross sections using the TNG nuclear reaction model code

Description: Theoretical gamma ray cross sections have been calculated using a nuclear reaction model code. These are compared to experimental gamma ray production cross sections obtained from neutron interactions with {sup 56}Fe at incident neutron energies of 1 to 40 MeV. The optical model and nuclear level density parameters in the code have been varied to affect a close agreement between calculations and the data. Present analyses, which focus on incident neutron energies between 17 and 40 MeV, display somewhat better agreement than those previously reported.
Date: April 1993
Creator: McCollam, K. J.
Partner: UNT Libraries Government Documents Department

INC Model interpretation of the proton induced residual nuclide production cross sections below 2 GeV

Description: For the purposes of interpreting the abundances of various isotopes in meteorites or on lunar and planetary surfaces exposed to fragmentation by cosmic rays, Webber et al. recently reported the measured total elemental and isotopic cross sections with heavy ions as projectiles on H, He, and C targets with beam energies of 0.33 - 1.7 GeV/nucleon. We employ the INC model to predict the fragmentation of the heavy ions in a hydrogen target with the inverse reaction process: proton bombardment of a heavy-ion nucleus leading to spallation products. Charge-changing and mass-changing cross sections are calculated for proton bombardment of an {sup 56}Fe target with beam energies ranging from 0.33 to 1.88 GeV. Total Z-changing and A-changing cross sections in the energy range 0.6 to 1.88 GeV are in excellent agreement with the corresponding experimental data of Webber et al. and Westfall at al., while the agreement below 0.6 GeV proton energy is not as good. The general trend of the Z-changing cross sections are reproduced by the model calculations at each proton incident energy. The interaction of 200-MeV protons with synthetic Stony Meteorite samples was undertaken to explain radionuclide production in a cosmic-ray environment. The BNL Linac 200-MeV-proton beam was used to irradiate synthetic Stony Meteorites to simulate cosmic-ray exposures corresponding to 6.4 and 16.4 million years. Each irradiated sample was analyzed with the help of a high-resolution gamma-ray spectrometer for long-lived radioisotopes. The intranuclear cascade code HETC was employed to simulate the 200-MeV proton bombardment on the meteorite samples to predict the radionuclides {sup 7}Be, {sup 22}Na, {sup 46}Mn, and {sup 56}Co produced in the experimental investigation.
Date: December 31, 1991
Creator: Divadeenam, M.; Ward, T. E.; Spergel, M. S.; Lakatos, S. & Manche, E. P.
Partner: UNT Libraries Government Documents Department

Experimental and calculated excitation functions for discrete-line gamma-ray production due to 1-40 MeV neutron interactions with sup 56 Fe

Description: Measuring cross sections for gamma-ray production from tertiary reactions is one of the ways to gain experimental information about these reactions. To this end, inelastic and other nonelastic neutron interactions with {sup 56}Fe have been studied for incident neutron energies between 0.8 and 41 MeV. An iron sample isotopically enriched in the mass 56 isotope was used. Gamma rays representing 70 transitions among levels in residual nuclei were identified, and production cross sections were deduced. The reactions studies were {sup 56}Fe(n,n{prime}){sup 56}Fe, {sup 56}Fe(n,p){sup 56}Mn, {sup 56}Fe(n,2n){sup 55}Fe, {sup 56}Fe(n,d + n,np){sup 55}Mn, {sup 56}Fe(n, t + n, nd + n,2np){sup 54}Mn, {sup 56}Fe(n,{alpha}){sup 53}Cr, {sup 56}Fe(n,n{alpha}){sup 52}Cr, and {sup 56}Fe(n,3n){sup 54}Fe. Experimental excitation functions have been compared with cross sections calculated using the nuclear reaction model code TNG, with generally favorable results. 24 refs., 2 figs.
Date: January 1, 1991
Creator: Dickens, J.K.; Fu, C.Y.; Hetrick, D.M.; Larson, D.C. & Todd, J.H.
Partner: UNT Libraries Government Documents Department

Multifragmentation and flow in central collisions of heavy systems

Description: Experimental results are presented on the production of light particles (A < 5) and intermediate mass fragments (6 < A < 18) over a large solid angle. The reactions 200 MeV/n Au + Au amd Au + Fe were studied to provide information on multifragmentation processes and collective flow. 20 refs., 6 figs.
Date: May 1, 1987
Creator: Harris, J.W.; Jacak, B.V.; Kampert, K.H.; Claesson, G.; Doss, K.G.R.; Ferguson, R. et al.
Partner: UNT Libraries Government Documents Department

High resolution inelastic gamma-ray measurements with a white neutron source from 1 to 200 MeV

Description: Measurements of prompt gamma rays following neutron-induced reactions have recently been made at the spallation neutron source at the WNR target area of LAMPF using germanium detectors. These experiments provide extensive excitation function data for inelastic neutron scattering as well as for other reactions such as (n,{alpha}), (n,n{alpha}), (n,p), (n,np), (n,nnp) and (n,xn) for 1 {le} {times} {le} 11. The continuous energy coverage available from 1 MeV to over 200 MeV is ideal for excitation function measurements and greatly extends the energy range for such data. The results of these measurements will provide a database for interpretation of gamma-ray spectra from the planned Mars Observer mission, aid in radiation transport calculations, allow verification of nuclear reaction models, and improve the evaluated neutron reaction data base.
Date: January 1, 1990
Creator: Nelson, R.O.; Laymon, C.M. & Wender, S.A.
Partner: UNT Libraries Government Documents Department

(Evaluations of neutron reactions with sup 52 Cr, sup 56 Fe, sup 58 Ni)

Description: The traveler organized and chaired the meeting of the NEANDC/NEACRP Nuclear Data Evaluation Cooperation Subgroup-I: Intercomparison of USA, European, and Japanese Evaluations for {sup 52}Cr, {sup 56}Fe, and {sup 58}Ni, held on December 3, 1990, at the NEA Data Bank in Saclay, France. The traveler held discussions with Subgroup-II members to keep track of the activities of this group in which the traveler is a member. Highlights and/or recommendations of these meetings, as well as observations of the EAF, EFF, and JEF meetings, are included in this report.
Date: December 21, 1990
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Capture in the 1. 15-keV iron resonance

Description: The 1.15-keV resonance in iron is important to reactors in that a major part of the iron capture integral is due to this one resonance. This resonance is also a good test case for capture gamma-ray detectors, which are meant to have an efficiency independent of gamma-ray energy spectra, because this resonance has an unusually hard spectrum and other iron resonances do not. There have been severe discrepancies among different groups who have measured the capture area and transmission of this resonance. A new measurement, employing C/sub 6/F/sub 6/ liquid scintillators and pulse-height weighting to effect total energy detection, has been made of the ratio of the capture area of the 22.8-keV resonance relative to that of the 1.15-keV resonance. The 22.8-keV resonance has a relatively soft gamma-ray spectrum and there is agreement on the capture area. The results (2.91 +- 0.17) agree well with transmission measurements and confirm the applicability of total energy detectors for use on capture resonances with very hard capture gamma-ray spectra.
Date: January 1, 1985
Creator: Weston, L.W. & Todd, J.H.
Partner: UNT Libraries Government Documents Department

International evaluation cooperation Task 1. 1: Intercomparison of evaluated files for sup 52 Cr, sup 56 Fe, and sup 58 Ni

Description: The cross sections and energy and angular distributions in the JENDL-3, JEF-2/EFF-2, and ENDF/B-VI evaluations for {sup 52}Cr, {sup 56}Fe, and {sup 58}Ni are compared graphically. The purpose is to understand the reasons for observed discrepancies among the evaluations, and to suggest recommendations for improvements. The accomplishments to date are presented.
Date: January 1, 1991
Creator: Fu, C.Y.; Larson, D.C.; Hetrick, D.M. (Oak Ridge National Lab., TN (USA)); Vonach, H. (Vienna Univ. (Austria)); Kopecky, J. (Netherlands Energy Research Foundation, Petten (Netherlands)); Iijima, S. (Toshiba Corp., Kawasaki (Japan). Nuclear Engineering Lab.) et al.
Partner: UNT Libraries Government Documents Department

Hypernuclear physics with the (/pi//sup +/, K/sup +/) reaction

Description: The study of hypernuclei affords unique insights into the nature of hadronic forces beyond those obtainable from ordinary nuclear physics research. A hypernucleus consists of one or more hyperons bound to a nuclear core. In the SU(3) classification, /Lambda/,/Sigma/, and /Xi/ hyperons occupy the same octet representation of spin-parity /1/2//sup +/ baryons as the neutron and proton, the familiar constituents of ordinary nuclei. The /Lambda/ and /Sigma/ possess strangeness S = /minus/1 and isotopic spin I = 0, 1, respectively, while the /Xi/ has S = /minus/2, I = /1/2/. In the underlying quark picture, the /Lambda/ and /Sigma/ have the flavor structure s(ud)/sub I=0, 1/, compared to the combination uud for the proton. The strange quark, s, carries the strangeness quantum number S = /minus/1, which makes it distinguishable from the S = 0 u and d quarks. The lowest-lying hyperon is the /Lambda/, with a mass of 1,115.6 MeV/c/sup 2/, some 177 MeV/c/sup 2/ heavier than the proton. The study of the behavior of a hyperon embedded in the nuclear medium, through the theoretical analysis of level spectra, sheds light on the nature of the hyperon-nucleon (YN) effective interaction, i.e. on the role of the strange quark in strong interactions. This paper investigates the (/pi//sup +/, K/sup +/) reactions that produce hypernuclei. 32 refs., 5 figs., 2 tabs.
Date: January 1, 1989
Creator: Millener, D.J. & Chrien, R.E.
Partner: UNT Libraries Government Documents Department

High-resolution structural material (n,x. gamma. ) production cross sections for 0. 2 < E/sub n/ less than or equal to 40 MeV

Description: An experimental program has been initiated at the Oak Ridge electron Linear Accelerator (ORELA) to measure yields of individual gamma rays resulting from interactions of 0.2- to 40-MeV neutrons with elements of structural materials of interest both for applied needs and basic research. In this paper we outline this program and present some cross-section results for /sup nat/Cr(n,x..gamma..) , /sup 56/Fe(n,x..gamma..) and /sup 58/Ni(n,x..gamma..). A good estimate of the total inelastic scattering cross section is obtained from the production cross section of the gamma ray corresponding to de-excitation of the first 2/sup +/ level in the even-even nuclides studied. In addition, cross sections for production of gamma rays resulting from tertiary reactions are measured, thus obtaining scarce cross-section information about these reactions.
Date: January 1, 1985
Creator: Larson, D.C.
Partner: UNT Libraries Government Documents Department

Calculation of neutron cross sections on iron up to 40 MeV

Description: The development of high energy d + Li neutron sources for fusion materials radiation damage studies will require neutron cross sections up to 40 MeV. Experimental data above 15 MeV are generally sparse or nonexistent, and reliance must be placed upon nuclear-model calculations to produce the needed cross sections. To satisfy such requirements for the Fusion Materials Irradiation Test Facility (FMIT), neutron cross sections have been calculated for /sup 54/ /sup 56/Fe between 3 and 40 MeV. These results were joined to the existing ENDF/B-V evaluation below 3 MeV. In this energy range, most neutron reactions can be described using the Hauser-Feshbach statistical model with corrections for preequilibrium and direct-reaction effects. To properly use these models to obtain realistic cross sections, emphasis must be placed upon the determination of suitable input parameters (optical model sets, gamma-ray strength functions, level densities) valid over the energy range of the calculation. To do this, several types of independent data were used to arrive at consistent parameter sets as described.
Date: January 1, 1980
Creator: Arthur, E.D. & Young, P.G.
Partner: UNT Libraries Government Documents Department

sup 56 Fe resonance parameters for neutron energies up to 850 keV

Description: High-resolution neutron measurements for {sup 56}Fe-enriched iron targets were made at the Oak Ridge Electron Linear Accelerator (ORELA) in transmission below 20 MeV and in differential elastic scattering below 5 MeV. Transmission measurements were also performed with a natural iron target below 160 keV. The transmission data were analyzed from 5 to 850 keV with the multilevel R-matrix code SAMMY which uses Bayes' theorem for the fitting process. This code provides energies and neutron widths of the resonances inside the 5- to 850-keV energy region, as well as possible parameterization for resonances external to the analyzed region to describe the smooth cross section from a few eV to 850 keV. The resulting set of resonance parameters yields the accepted values for the thermal total and capture cross sections. The differential elastic-scattering data at several scattering angles were compared to theoretical calculations from 40 to 850 keV using the R-matrix code RFUNC based on the Blatt-Biedenharn formalism. Various combinations of spin and parity were tried to predict cross sections for the well defined {ell} > 0 resonances; comparison of these predictions with the data allowed us to determine the most likely spin and parity assignments for these resonances. The results of a capture data analysis by Corvi et al. (COR84), from 2 to 350 keV, were combined with our results to obtain the radiation widths of the resonances below 350 keV observed in transmission, capture, and differential elastic-scattering experiments.
Date: December 1, 1990
Creator: Perey, C.M.; Perey, F.G.; Harvey, J.A.; Hill, N.W. & Larson, N.M.
Partner: UNT Libraries Government Documents Department

Recent results in the development of a global medium-energy nucleon-nucleus optical-model potential

Description: Initial results are presented for the determination of a global medium-energy nucleon-nucleus phenomenological optical-model potential using a relativistic Schroedinger representation. The starting point for this work is the global phenomenological optical-model potential of Schwandt )ital et al.), which is based on measured elastic scattering cross sections and analyzing power for polarized protons ranging from 80 to 180 MeV. This potential is optimally modified to reproduce experimental proton reaction cross sections as a function of energy, while allowing only minimal deterioration in the fits to the elastic cross sections and analyzing powers. Further modifications in the absorptive potential were found necessary to extrapolate the modified potential to higher energies. The final potential is converted to a neutron-nucleus potential by use of standard Lane model assumptions and by accounting approximately for the Coulomb correction. Comparisons of measured and calculated proton reaction and neutron total cross sections are presented for /sup 27/Al, /sup 56/Fe, and /sup 208/Pb. Medium-energy optical-model potentials for complex projectiles are briefly discussed in an appendix. 7 refs., 20 figs
Date: February 1, 1988
Creator: Madland, D.G.
Partner: UNT Libraries Government Documents Department

Analysis of Fe(n,x[gamma]) cross sections using the TNG nuclear reaction model code

Description: Theoretical gamma ray cross sections have been calculated using a nuclear reaction model code. These are compared to experimental gamma ray production cross sections obtained from neutron interactions with [sup 56]Fe at incident neutron energies of 1 to 40 MeV. The optical model and nuclear level density parameters in the code have been varied to affect a close agreement between calculations and the data. Present analyses, which focus on incident neutron energies between 17 and 40 MeV, display somewhat better agreement than those previously reported.
Date: April 1, 1993
Creator: McCollam, K.J.
Partner: UNT Libraries Government Documents Department