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An update on measurements of helium-production reactions with a spallation neutron source

Description: This report gives the status, updated since the last Research Coordination Meeting, of alpha-particle production cross sections, emission spectra and angular distributions which we are measuring at the spallation source of fast neutrons at the Los Alamos Meson Physics Facility (LAMPF). Detectors at angles of 30, 60, 90 and 135{degrees} are used to identify alpha particles, measure their energy spectra, and indicate the time-of-flight, and hence the energy, of the neutrons inducing the reaction. The useful neutron energy ranges from less than 1 MeV to approximately 50 MeV for the present experimental setup. Targets under study at present include C, N, 0, {sup 27}Al, Si, {sup 51}V, {sup 56}Fe, {sup 59}CO, {sup 58,60}Ni, {sup 89}Y and {sup 93}Nb. Data for {sup 59}Co have been re-analyzed. The results illustrate the capabilities of the approach, agreement with literature values, and comparisons with nuclear reaction model calculations.
Date: October 1, 1995
Creator: Haight, R.C.; Bateman, F.B. & Chadwick, M.B.
Partner: UNT Libraries Government Documents Department

Absolute measurement of the critical scattering cross section in cobalt

Description: Small-angle neutron scattering techniques have been used to study the angular distribution of the critical scattering from cobalt above T/sub c/. These measurements have been put on an absolute scale by calibrating the critical scattering directly against the nuclear incoherent scattering from cobalt. In this way the interaction range r$sub 1$, which appears in the classical and modified Ornstein--Zernike expressions for the asymptotic form of the spin pair correlation function and is related to the strength of the spin correlations, has been determined. We obtain r$sub 1$/a = 0.46 +- 0.03 for the ratio of the interaction range to the nearest-neighbor distance in cobalt. This result is in good agreement with theoretical predictions. Lack of agreement among previous determinations of the ratio r$sub 1$/a made in iron failed to provide a definitive comparison with theory. (auth)
Date: January 1, 1975
Creator: Glinka, C. J.; Minkiewicz, V. J. & Passell, L.
Partner: UNT Libraries Government Documents Department

Production Test No. 105-511-A -- Irradiation of stainless steel samples

Description: This study soughs to determine the x-ray activity of two samples of stainless steel prepared from tubing used in the ANL-140, in-pile experiment (P-13). This information is necessary in order to predict the activity of the P-13 rig at the time of removal. The primary contribution to the over-all activity will be from Ta{sup 181} and Co{sup 59} impurities.
Date: April 2, 1952
Creator: Gillard, C. W.
Partner: UNT Libraries Government Documents Department

Evidence for the synthesis of {sup 267}110 produced by the {sup 59}Co + {sup 209}Bi reaction

Description: An experiment to synthesize element 110 by the {sup 59}Co+{sup 209}Bi reaction has bee performed at the SuperHILAC at the Lawrence Berkeley Laboratory. One event with many of the expected characteristics of a successful of {sup 267}110 was observed. This event corresponds to a production cross section of about one picobarn.
Date: September 1, 1994
Creator: Ghiorso, A.; Lee, D. & Somerville, L. P.
Partner: UNT Libraries Government Documents Department

Cobalt-60 production at Savannah River

Description: Over the past 8 or 9 years, the Savannah River Plant (SRP) has produced close to 4 million curies of cobalt-60 by irradiating cobalt-59 in the production reactors. This paper reviews past and current irradiations, cobalt-60 production methods, and costs.
Date: February 1, 1995
Creator: Allen, H. F.
Partner: UNT Libraries Government Documents Department

Influence of point defects on grain boundary diffusion in oxides. Final technical report, July 1, 1990--June 30, 1993

Description: Grain boundary diffusion coefficients of {sup 57}Co and {sup 59}Co in polycrys. NiO, NiO bicrystal, and polycrys. Fe{sub 3}O{sub 4} were determined at various oxygen pressures at 750 C. For NiO, the low oxygen pressure region (<10{sup {minus}10} MPa) displayed constant grain boundary diffusion coefficients as the oxygen pressure decreased, indicating an extrinsic region in which the impurity-induced defects dominated the intrinsic defects. At greater oxygen pressures, the intrinsic defects (Ni vacancies) dominated the extrinsic defects, causing the diffusion to increase with pressure. For Fe{sub 3}O{sub 4}, at low oxygen pressures (<10{sup {minus}16} MPa), the grain boundary diffusion coefficient increased when the pressure decreased, owing to interstitial type diffusion; at >10{sup {minus}15} MPa, the diffusion increased with pressure, owing to vacancy type diffusion. D{sub gb} of Co ions in Fe{sub 3}O{sub 4} is proportional to pO{sub 2}{sup {minus}2/3} in the low pressure region and to pO{sub 2}{sup 2/3} in the high pressure region, indicating similar mechanisms in the grain boundary diffusion and volume diffusion. Ratio of D{sub gb}/D was about 10{sup 3}.
Date: November 1, 1993
Creator: Stubican, V. S.
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

The {sup 59}Co(n,{alpha}) reaction from threshold to 30 MeV

Description: Neutron-induced reactions that result in alpha-particle emission have been investigated for the target nucleus {sup 59}Co over the neutron energy range from threshold to 30 MeV with the spallation neutron source at WNR/LAMPF. Double-differential cross sections were measured at alpha-particle emission angles of 30, 60, 90 and 135{degree}. Integrated cross sections agree well with activation data below 14 MeV where only the {sup 59}Co(n,{alpha}){sup 56}Mn reaction contributes to alpha-particle emission. At higher energies, the integrated alpha-particle emission cross section exceeds the activation data. The results will be interpreted in terms of statistical and pre-compound reaction mechanisms. The sensitivity to nuclear level density parameters will be discussed.
Date: June 1, 1994
Creator: Lee, T. M.; Sterbenz, S. M. & Bateman, F. B.
Partner: UNT Libraries Government Documents Department

An evaluated neutronic data file for elemental cobalt

Description: A comprehensive evaluated neutronic data file for elemental cobalt is described. The experimental data base, the calculational methods, the evaluation techniques and judgments, and the physical content are outlined. The file contains: neutron total and scattering cross sections and associated properties, (n,2n) and (n,3n) processes, neutron radiative capture processes, charged-particle-emission processes, and photon-production processes. The file extends from 10/sup /minus/5/ eV to 20 MeV, and is presented in the ENDF/B-VI format. Detailed attention is given to the uncertainties and correlations associated with the prominent neutron-induced processes. The numerical contents of the file have been transmitted to the National Nuclear Data Center, Brookhaven National Laboratory. 143 refs., 16 figs., 5 tabs.
Date: August 1, 1988
Creator: Guenther, P.; Lawson, R.; Meadows, J.; Sugimoto, M.; Smith, A.; Smith, D. et al.
Partner: UNT Libraries Government Documents Department

Pauli-blocking effects in neutron-alpha reactions

Description: We present a knockout model for direct (n,{alpha}) reactions in which the residual nucleus is left in a continuum excited state. The interaction of the neutron with a preformed alpha particle inside the nucleus is related to the free neutron-alpha scattering cross-section, with modifications to account for nuclear medium effects, including Fermi motion, Pauli-blocking, and barrier penetration. Phase space restrictions for the four nucleons of the alpha-particle after the knockout are imposed by a Pauli-blocking function. We apply this model, along with evaporation contributions, to analyze excitation functions of (n,{alpha} reactions on {sup 48}Ti, {sup 51}V, {sup 52}Cr, {sup 54}Fe, {sup 55}Mn, and {sup 59}Co. Good agreement is obtained between our calculations and experimental measurements. Values for the local Fermi energy in the region from where knockout occurs indicate a surface reaction.
Date: June 1, 1994
Creator: Avrigeanu, M.; Avrigeanu, V.; Antonov, A. N.; Chadwick, M. B.; Hodgson, P. E. & Stoitsov, M. V.
Partner: UNT Libraries Government Documents Department

Gamma emission in precompound reactions: 2, Numerical application

Description: The analytically obtained results of the preceding paper on capture gamma ray reactions are used for a direct numerical calculation. It turns out that this formulation allows for a parameter free description of gamma emission in precompound reactions. As an example we choose reactions induced by 14.1 MeV neutrons incident on {sup 59}CO, {sup 93}Nb and {sup 181}Ta. The individual contributions of different terms to the total cross section are discussed in detail and a comparison to experimental data is pursued.
Date: September 1, 1992
Creator: Herman, M.; Reffo, G. & Hoering, A.
Partner: UNT Libraries Government Documents Department


Description: The H-F conductance and susceptance were determined for coil-type vessels over a range of frequencies from 2 to 30 mc. The ultraviolet absorption spectra of organic compounds in the vapor phase were determined, and a maximum was assigned to each compound. The dielectric constant values for five alpha substituted ketones at 25 deg C are reponted. A series of acids in dimethylformamide was titrated with the alkali methoxides by the high-frequency and conductance methods. The titration curves by these two methods were very similar in shape and also very similar to the curves for the corresponding type of acid in aqueous solution (W.L.H.)
Date: September 14, 1959
Partner: UNT Libraries Government Documents Department

Some fundamental aspects of the optical potential for the interaction of fast neutrons with cobalt

Description: Differential elastic- and inelastic-scattering cross sections, measured from approx.1.5 to 10.0 MeV, are interpreted in terms of spherical-optical-statistical (OM) and coupled-channels models. A successful description of the differential elastic scattering below 10 MeV and the total cross section to 20.0 MeV is achieved using the spherical OM with energy-dependent strengths and geometries. These energy dependencies are large below approx.7.0 MeV, but become smaller and similar to those reported for /open quotes/global/close quotes/ potentials at higher energies. This change in the energy dependence of the parameters probably marks the onset of the Fermi surface anomaly approx.19 MeV above the Fermi energy. Inelastic scattering to the levels below 1.8 MeV displays a forward-peaked behavior. This nonstatistical component is interpreted using the weak-coupling model in which the f/sub 7/2 proton hole is coupled to the 2/sup /plus// state in /sup 60/Ni. This model provides an explanation of the unusual energy dependence and relatively small radius found for the imaginary OM potential. The coupling also contributes to the large value of this potential. The real spherical OM potential derived from the neutron-scattering results is extrapolated to bound energies by using the dispersion relationship and the method of moments. The resulting real-potential strength and radius peak at approx.-10.0 MeV, whereas the real diffuseness is at a minimum at this energy. The extrapolated potential is approx.8% larger than that implied by reported particle-state energies, and approx.13% smaller than indicated by hole-state energies. 42 refs., 8 figs.
Date: January 1, 1988
Creator: Smith, A.B. & Lawson, R.D.
Partner: UNT Libraries Government Documents Department

Cobalt, fast neutrons and physical models: Nuclear data and measurements series

Description: Energy-averaged neutron total cross sections of cobalt were measured from approx. =0.5 to 12.0 MeV. Differential elastic- and inelastic-scattering cross sections were measured from approx. =1.5 to 10.0 MeV over the scattering-angle range approx. =18/sup 0/ to 160/sup 0/, with sufficient detail to define the energy-averaged behavior. Inelastic neutron groups were observed corresponding to ''levels'' at: 1115 +- 29, 1212 +- 24, 1307 +- 24, 1503 +- 33, 1778 +- 40, 2112 +- 40, 2224 +- 35, 2423 +- 39, 2593 +- 41 and 2810 keV. The experimental results were interpreted in terms of the spherical optical-statistical and coupled-channels models. An unusually successful description of observables was achieved over a wide energy range (<-15.0 to > 20.0 MeV) with a spherical model having energy-dependent strengths and geometries. The energy dependencies are large below approx. =7.0 MeV (i.e., approx. =19.0 MeV above the Fermi energy), but become smaller and similar to those reported for ''global'' potentials at higher energies. The imaginary strength is large and decreases with energy. These imaginary-potential characteristics are attributed to neutron shell closure and collective-vibrational processes. The weak-coupling model also offers an explanation of the unusual negative energy slope and relatively small radius of the imaginary potential. The spherical optical model derived from the neutron-scattering results was extrapolated to bound energies using the dispersion relationship and the method of moments. The resulting real-potential strength and radius peak at approx. =-10.0 MeV, while concurrently the real diffuseness is at a minimum. The extrapolated potential is approx. =8% larger than that implied by reported particle-state energies, and approx. =13% smaller than indicated by hole-state energies. 68 refs., 15 figs., 1 tab.
Date: July 1, 1987
Creator: Smith, A.B.; Guenther, P.T.; Whalen, J.F. & Lawson, R.D.
Partner: UNT Libraries Government Documents Department

Neutron capture cross section standards for BNL 325, Fourth Edition

Description: This report evaluates the experimental data and recommends values for the thermal neutron cross sections and resonance integrals for the neutron capture reactions: /sup 55/Mn(n,..gamma..), /sup 59/Co(n,..gamma..) and /sup 197/Au(n,..gamma..). The failure of lithium and boron as standards due to the natural variation of the absorption cross sections of these elements is discussed. The Westcott convention, which describes the neutron spectrum as a thermal Maxwellian distribution with an epithermal component, is also discussed.
Date: January 1, 1981
Creator: Holden, N.E.
Partner: UNT Libraries Government Documents Department

Oxo chemistry in supercritical carbon dioxide

Description: We report an investigation of the cobalt carbonyl-catalyzed oxo process in supercritical CO{sub 2} using in situ high pressure NMR spectroscopy. The use of supercritical CO{sub 2} as the solvent medium eliminates gas-liquid mixing problems. The effect of supercritical CO{sub 2} on the oxo reaction was determined by comparing the linear to branched aldehyde yield and rate and other equilibrium processes involved in the catalytic cycle with measured values in conventional liquid solvents.
Date: January 1, 1991
Creator: Krause, T.R.; Rathke, J.W. & Klingler, R.J.
Partner: UNT Libraries Government Documents Department

Recoil spectrometer for the detection of single atoms

Description: A much improved version of our gas-filled spectrometer for heavy-ion-induced fusion reactions is described. This instrument (SASSY II) is of the type D-Q-D wherein the dipoles are made with strong vertically-focussing gradients. The problems associated with experiments with cross sections in the picobarn range are discussed. In such experiments, it is necessary to identify single atoms with a high degree of confidence.
Date: April 1, 1987
Creator: Ghiorso, A.
Partner: UNT Libraries Government Documents Department

ENDF/B-VI nuclear data evaluations for fusion applications

Description: The next release of the ENDF/B data library planned for 1989 contains improved data evaluations of interest to the fusion neutronics community. New data formats permit inclusion of energy-angle correlated particle emission spectra and recoil nucleus energy spectra. Enhanced formats for covariance information have been developed. Many new isotopic evaluations will lead to improved energy conservation and kerma factor calculations. Improved nuclear model calculations will provide reliable particle emission data where experimental information is sparse. Improved Bayssian fitting codes will provide more accurate evaluations for data rich reactions such as Li(n,nt)..cap alpha... All of the most important fusion material evaluations contain these new features. 32 refs., 8 figs.
Date: January 1, 1988
Creator: Dunford, C.L.; Larson, D.C. & Young, P.G.
Partner: UNT Libraries Government Documents Department