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1/2/sup +/. -->. 1/2/sup -/ beta decay of /sup 19/Ne and the parity nonconserving NN force

Description: A branching ratio of (1.20 +- 0.20) x 10/sup -4/ is obtained for the ..beta../sup +/ decay of /sup 19/Ne to the 110 keV 1/2/sup -/ level of /sup 19/F. This transition (presumably dominated by the ..delta..J/sup ..pi../ = 0/sup -/ axial charge operator) provides a crucial test of wavefunctions used in interpreting the parity mixing of the ground and 110 keV levels of /sup 19/F. These wavefunctions, which yield a parity mixing larger than that observed experimentally, also predict too large a ..beta../sup +/ decay rate.
Date: January 1, 1978
Creator: Adelberger, E.G.; Hindi, M.M.; Hoyle, C.D.; Swanson, H.E. & Von Lintig, R.D.
Partner: UNT Libraries Government Documents Department

Magnetic radius of the deuteron

Description: The root-mean square radius of the deuteron magnetic moment distribution, r{sub Md}, is calculated for several realistic models of the NN-interaction. For the Paris potential the result is r{sub Md} = 2.312 {+-} 0.010 fm. The dependence of r{sub Md} on the choice of NN model, relativistic effects and meson exchange currents is investigated. The experimental value of r{sub Md} is also considered. The necessity of new precise measurements of the deuteron magnetic form factor at low values of Q{sup 2} is stressed.
Date: August 1, 1998
Creator: Afanasev, Andrei; Afanasev, V.D. & Trubnikov, S.V.
Partner: UNT Libraries Government Documents Department

The Decay of Neptunium-238

Description: >A study was made of the energy levels of Pu/sup 238/ which are populated by Np/sup 238/ beta decay, by an examination of the Np/sup 238/ conversion electron spectrum in high-resolution beta spectrographs. The general features of the level scheme as previously given were unchanged but several new transitions were observed, with energies of 119.8, 871, 943, 989, and 1034 kev. Two new levels are postulated at 915 and 1034 kev which accommodate all but the 943-kev transition. A possible assignment of the 943-kev transition to the (0+.0) state of the beta vibrational band is discussed. In addition, the weak 885-kev transition from the 2+ state of the gamma -vibrational band to the 4+ state of the ground band was seen and its relative intensity determined. Comparisons were made of the experimental relative transition intensities of the three photons depopulating this band with those predicted from the rules of Alaga et al.; only fair agreement was noted. A discussion is given of the beta decay branchings and log ft values of Np/sup 238/ decay in terms of the postulated characters of the Pu/sup 238/ states and the measured spin of Np/sup 238/. (auth)
Date: December 1, 1960
Creator: Albridge, R. G. & Hollander, J. M.
Partner: UNT Libraries Government Documents Department

Incomplete and complete fusion in intermediate energy heavy ion reactions

Description: The yields, angular distributions and differential range spectra have been measured for individual target residues from the interaction of 8.5 MeV/A /sup 16/O, 19 MeV/A /sup 16/O, 35 MeV/A /sup 12/C and 86 MeV/A /sup 12/C with /sup 154/Sm. From the measured data, fragment isobaric yields and velocity spectra were deduced. The results are compared to the sum rule model of Wilczyski et al. and the nuclear firestreak model. 18 references.
Date: March 1, 1984
Creator: Aleklett, K.; Loveland, W.; Sugihara, T.T.; Morrissey, D.J.; Wenxin, L.; Kot, W. et al.
Partner: UNT Libraries Government Documents Department

Pion production in relativistic collisions of nuclear drops

Description: In a continuation of the long-standing effort of the nuclear physics community to model atomic nuclei as droplets of a specialized nuclear fluid, we have developed a hydrodynamic model for simulating the collisions of heavy nuclei at relativistic speeds. Our model couples ideal relativistic hydrodynamics with a new Monte Carlo treatment of dynamic pion production and tracking. The collective flow for low-energy (200 MeV/N) collisions predicted by this model compares favorably with results from earlier hydrodynamic calculations which used quite different numerical techniques. Our pion predictions at these lower energies appear to differ, however, from the experimental data on pion multiplicities. In this case of ultra-relativistic (200 GeV/N) collisions, our hydrodynamic model has produced baryonic matter distributions which are in reasonable agreement with recent experimental data. These results may shed some light on the sensitivity of relativistic collision data to the nuclear equation of state. 20 refs., 12 figs.
Date: September 1, 1988
Creator: Alonso, C.T.; Wilson, J.R.; McAbee, T.L. & Zingman, J.A.
Partner: UNT Libraries Government Documents Department

Low-energy particle production and residual nuclei production from high-energy hadron-nucleus collisions

Description: The high-energy hadron-nucleus collision model, EVENTQ, has been modified to include a calculation of the excitation and kinetic energy of the residual compound nucleus. The specific purpose of the modification is to make it possible to use the model in the high-energy radiation transport code, HETC, which, in conjunction with MORSE, is used to transport the low energy particles. It is assumed that the nucleons in the nucleus move in a one-dimensional potential well and have the momentum distribution of a degenerate Fermi gas. The low energy particles produced by the deexcitation of the residual compound nucleus, and the final residual nucleus, are determined from an evaporation model. Comparisons of multiplicities and residual nuclei distributions with experimental data are given. The ''grey'' particles, i.e., charged particles with 0.25 < ..beta.. < 0.7, are in good agreement with experimental data but the residual nuclei distributions are not. 12 refs., 3 figs.
Date: January 1, 1987
Creator: Alsmiller, F.S.; Alsmiller, R.G. Jr. & Hermann, O.W.
Partner: UNT Libraries Government Documents Department

Calculated particle production spectra and multiplicities from nucleon-fissile element collisions at medium energies

Description: A fission channel was added to the intranuclear-cascade-evaporation model of nuclear reactions so that this model could be used to obtain the differential particle production data that are needed to study the transport of medium-energy nucleons and pions through matter. The earlier work of Hahn and Bertini on the incorporation of fission-evaporation competition into the intranuclear-cascade-evaporation model was retained, and the statistical model of fission was utilized to predict particle production from the fission process. Approximate empirically derived kinetic energies and deformation energies are used in the statistical model. The calculated residual nuclei distributions are in reasonable agreement with experimental data, but the neutron multiplicities at the higher incident nucleon energies greater than or equal to 500 MeV are sensitive to the level density parameter used. 4 figures.
Date: January 1, 1979
Creator: Alsmiller, F.S.; Alsmiller, R.G. Jr.; Gabriel, T.A.; Lillie, R.A. & Barish, J.
Partner: UNT Libraries Government Documents Department

Phenomenological model for particle production from the collision of nucleons at medium energies with fissile elements

Description: A detailed fission channel, including fragment mass, charge, kinetic energy, and excitation energy distributions, has recently been added to the evaporation stage of the Monte Carlo code MECC-7 for nuclear cross sections and particle production. In this code the intranuclear-cascade-evaporation model is applied to nucleon and pion nonelastic reactions at energies between 20 MeV and 3 GeV. The present paper discusses significant revisions to the model. Calculated fission-neutron multiplicities are tabulated for /sup 235/U, /sup 238/U, and /sup 239/Pu. 1 table. (RWR)
Date: January 1, 1980
Creator: Alsmiller, F.S.; Alsmiller, R.G. Jr.; Gabriel, T.A.; Lillie, R.A. & Barish, J.
Partner: UNT Libraries Government Documents Department

Heavy-Ion Elastic Scattering

Description: The elastic scattering of C/sup 12/ ions from Ar, Fe, Ni, Ag/sup 107/ In, and Ta was measured as a function of angle, at a laboratory-system energy of 124.5 Mev with the Berkeley heavy-ion linear accelerator. The experimental equipment and techniques are discussed. The angular distributions show the same general behavior as previous heavy-ion elastic scattering experiments. The experimental data were analyzed with the semiclassical Blair model as modified by McIntyre. Very good agreement with experiment was obtained. The measurements were taken with 1% statistics in order to study the structure of the angular distributions in greater detail, because only by fitting the details in the structure was it possible to obtdin unambiguous sets of parameters. The parameters indicated a nuclear radius of 1.45A/sup 1/3/ x 10/sup -13/ cm, and a nearly constant surface thick ness of 1.6 x 10/sup -13/ cm. Total reaction cross sections were obtained. A rainbow-model analysis by Goldman of the data is given. Existing alpha - and heavy-ion scattering data were analyzed with the McIntyre model and compared with previous optical-model analyses of the same data. It was found that, by independent analysis, the two models give the same imaginary phase shifts for all partial waves. The real phase shifts are identical above a certain lth partial wave, but differ widely below this 1 value. It is shown that in the region of disagreement the real part of the phase shifts is irrelevant to the calculation of the cross section. (auth)
Date: April 17, 1961
Creator: Alster, Jonas
Partner: UNT Libraries Government Documents Department

Alternate Approach to the 239Pu(n,2n) Cross Section

Description: Using existing experimental data for neutron-induced total, elastic, inelastic, reaction and fission cross sections, as well as results from nuclear model calculations and evaluations from nuclear reaction data libraries, we derived an estimate for the cross sections for the {sup 235}U(n,2n) and {sup 239}Pu(n,2n) reactions for the neutron energy range from threshold to approximately 12 MeV. In effect, our approach is based on subtracting the fission and inelastic cross sections from the total reaction cross section where the difference is expected to yield the (n,2n) cross section. In addition to this subtraction approach, a ratio method and a differential method have also been explored. For {sup 235}U(n,2n), as a test case, we arrive at a cross section consistent with previous measurements, and for {sup 239}Pu(n,2n) we obtain a peak value of 400 {+-} 60 mb for the incident neutron energy range of 10 {le} E{sub n} {le} 12 MeV.
Date: September 1, 2000
Creator: Anderson, J D; Bauer, R W; Becker, J A; Dietrich, F S & McNabb, D P
Partner: UNT Libraries Government Documents Department

How do nuclei really vibrate or rotate

Description: By means of the adiabatic cranking model the properties of the current and velocity fields of nuclear quadrupole vibrations for even-even nuclei in the rare-earth region are investigated. BCS correlated wave functions based on the Nilsson single particle Hamiltonian have been used. The current fields are analyzed in terms of vector spherical harmonics. The realistic microscopic currents show a vortex structure not present in the classical irrotational flow. The microscopic origin of the vortex structure is investigated.
Date: January 1, 1983
Creator: Andresen, H.G.; Kunz, J.; Mosel, U.; Mueller, M.; Schuh, A. & Wust, U.
Partner: UNT Libraries Government Documents Department

Predictions for nuclear properties along the r-process path

Description: The uniformity of different nuclear regions as a function of the number of valence protons and neutrons (counted from the nearest closed shell) has been exploited for the parameterization of calculations for nuclei far from stability within the IBA model. Predictions are given for low lying levels, E2 transition rates, and binding energies for nuclei in the r-process path in the A = 150 and A = 190 mass regions. 6 refs., 6 figs.
Date: October 15, 1987
Creator: Aprahamian, A.
Partner: UNT Libraries Government Documents Department

Spin-flip (p,n) reactions on /sup 26/Mg, /sup 54/Fe, and /sup 56/Fe at selected proton bombarding energies in the range of 17 to 25 MeV

Description: New data are presented for the /sup 26/Mg(p,n)/sup 26/Al reaction at E/sub p/ = 19.12 and 24.97 MeV, for the /sup 54/Fe(p,n)/sup 54/Co reaction at E/sub p/ = 17.20, 18.60, and 24.60 MeV, and for the /sup 56/Fe(p,n)/sup 56/Co reaction at E/sub p/ = 19.12 and 24.59 MeV. Data were taken with the LLNL Cyclograaff at 16 angles from 3.5/sup 0/ to 159.0/sup 0/. A large detector at 23.8/sup 0/ with a long neutron flight path collected high resolution spectra. This large detector also collected separate 0/sup 0/ high resolution data on the /sup 26/Mg and /sup 56/Fe(p,n) reactions at E/sub p/ = 19 MeV. Absolute differential (p,n) cross sections were extracted for 1/sup +/ states in /sup 26/Al, /sup 54/Co, and /sup 56/Co, for the 0/sup +/ isobaric analong state (IAS) in /sup 54/Co and /sup 56/Co, for a 2/sup +/ state in each residual nucleus, and for the 0.199 MeV 7/sup +/ state of /sup 54/Co. No new experimental states were identified. Only relative cross sections were extracted at 0/sup 0/. Experimental angle-integrated cross sections were obtained for all but one state. DWBA79 was used, with the G-matrix effective nucleon-nucleon interaction of Bertsch et al. (with the central triplet-odd component V/sub to/ = O) and the Livermore shell model wave functions to calculate differential (p,n) cross sections to 1/sup +/ states and to the /sup 54/Co and /sup 56/Co IAS. Normalization of the DWBA angle-integrated cross sections to measurements for the /sup 54/Co and /sup 56/Co IAS (at E/sub p/ = 24.6 MeV) yielded the renormalized V/sub tau/ = 21.4 +- 2.1 MeV. Normalization of the DWBA angle-integrated cross sections to measurements for the 24.6 MeV /sup 54/Co and /sup 56/Co 1/sup +/ states, coupled with the normalization of the wave functions to previously experimentally determined GT strength, ...
Date: June 1, 1985
Creator: Aron, D.L.
Partner: UNT Libraries Government Documents Department

The GNASH preequilibrium-statistical nuclear model code

Description: The following report is based on materials presented in a series of lectures at the International Center for Theoretical Physics, Trieste, which were designed to describe the GNASH preequilibrium statistical model code and its use. An overview is provided of the code with emphasis upon code's calculational capabilities and the theoretical models that have been implemented in it. Two sample problems are discussed, the first dealing with neutron reactions on /sup 58/Ni. the second illustrates the fission model capabilities implemented in the code and involves n + /sup 235/U reactions. Finally a description is provided of current theoretical model and code development underway. Examples of calculated results using these new capabilities are also given. 19 refs., 17 figs., 3 tabs.
Date: January 1, 1988
Creator: Arthur, E. D.
Partner: UNT Libraries Government Documents Department

Development and benchmarking of higher energy neutron transport data libraries

Description: Neutron cross-section evaluations covering the energy range from 10/sup /minus/11/ to 100 MeV have been prepared for several materials. The principal method used to generate this data base has employed statistical-preequilibrium nuclear models, sophisticated phase shift analyses, and R-matrix techniques. The library takes advantage of formats developed for Version 6 of the Evaluated Nuclear Data File, ENDF. Methods to efficiently utilize the ENDF/B-VI representation of this library in the MCNP Monte Carlo code have been developed. MCNP results using the new library have been compared with calculated results using codes or data based upon intranuclear cascade models. 7 refs., 8 figs.
Date: January 1, 1988
Creator: Arthur, E. D.; Young, P. G.; Perry, R. T.; Madland, D. G.; MacFarlane, R. E.; Little, R. C. et al.
Partner: UNT Libraries Government Documents Department

Neutron cross section calculations for fission-product nuclei. [0. 001 to 20 MeV, Hauser-Feshbach theory]

Description: To satisfy nuclear data requirements for fission-product nuclei, Hauser-Feshbach statistical calculations with preequilibrium corrections for neutron-induced reactions on isotopes of Se, Kr, Sr, Zr, Mo, Sn, Xe, and Ba between 0.001 and 20 MeV. Spherical neutron optical parameters were determined by simultaneous fits to resonance data and total cross sections. Isospin coefficients appearing in the optical potentials were determined through analysis of the behavior of s- and p-wave strengths as a function of mass for a given Z. Gamma-ray strength functions, determined through fits to stable-isotope capture data, were used in the calculation of capture cross sections and gamma-ray competition to particle emission. The resulting (n,..gamma..), (n,n'), (n,2n), and (n,3n) cross sections, the secondary neutron emission spectra, and angular distributions calculated for 19 fission products will be averaged to provide a resulting ENDF-type fission-product neutronics file. 11 references.
Date: January 1, 1979
Creator: Arthur, E.D. & Foster, D.G. Jr.
Partner: UNT Libraries Government Documents Department

Calculation of neutron cross sections for tungsten isotopes. [Pre-equilibrium statistical model, 1 to 20 MeV preliminary calculations]

Description: Neutron-induced cross sections on tungsten isotopes were calculated in the energy range between 1 and 20 MeV using preequilibrium-statistical model techniques. The success of these calculations, which form part of an effort to improve the evaluated neutron and gamma-ray production cross sections for tungsten appearing in ENDF/B, depends strongly on the determination of consistent input parameter sets applicable over the entire range of interest. For example, neutron optical model parameters were derived through a simultaneous analysis of total cross sections, resonance data, and angular distributions. These parameters, when used in multistep Hauser-Feshbach calculations, produce good agreement with varied experimental data such as neutron inelastic scattering excitation functions and (n, 2n) cross sections. Likewise, gamma-ray strength functions were determined through fits to neutron capture data that produce calculated results that compare well to measured gamma-ray production cross sections. A description of the techniques used in such parameter determinations as well as comparison of calculated results to experimental data will be presented.
Date: January 1, 1979
Creator: Arthur, E.D. & Philis, C.A.
Partner: UNT Libraries Government Documents Department

Nuclear models relevant to evaluation

Description: The widespread use of nuclear models continues in the creation of data evaluations. The reasons include extension of data evaluations to higher energies, creation of data libraries for isotopic components of natural materials, and production of evaluations for radiative target species. In these cases, experimental data are often sparse or nonexistent. As this trend continues, the nuclear models employed in evaluation work move towards more microscopically-based theoretical methods, prompted in part by the availability of increasingly powerful computational resources. Advances in nuclear models applicable to evaluation will be reviewed. These include advances in optical model theory, microscopic and phenomenological state and level density theory, unified models that consistently describe both equilibrium and nonequilibrium reaction mechanism, and improved methodologies for calculation of prompt radiation from fission. 84 refs., 8 figs.
Date: January 1, 1991
Creator: Arthur, E.D.; Chadwick, M.B.; Hale, G.M. & Young, P.G.
Partner: UNT Libraries Government Documents Department

Applied uses of level density models

Description: This paper addresses issues associated with the use of nuclear level density models in calculations made for data applications. The two most commonly used models, the Gilbert Cameron and the Back-Shifted Fermi Gas, are briefly summarized and examples are provided of recent efforts to improve their parameterization. Calculated particle emission spectra are compared with recent experimental data in order to assess performance and sensitivity to these models. Extrapolation of nuclear level densities for calculations involving nuclei away from stability poses special problems and examples of recent efforts to improve such extrapolations are cited. The sensitivity of current schemes in the modeling of fission transition state densities are explored through calculated (n,f) cross sections. Two newer phenomenological models, those of Ignatyuk and Schmidt, provide a more physically realistic description of level densities. Calculations concerning {sup 207}Pb(n,xn) cross sections compare results using the Ignatyuk formalism with the Gilbert Cameron results. 31 refs., 10 figs.
Date: January 1, 1989
Creator: Arthur, E.D.; Guenther, P.T.; Smith, A.B.; Smith, D.L. (Los Alamos National Lab., NM (USA) & Argonne National Lab., IL (USA))
Partner: UNT Libraries Government Documents Department

Dynamics of density fluctuations in a non-Markovian Boltzmann- Langevin model

Description: In the course of the past few years, the nuclear Boltzmann-Langevin (BL)model has emerged as a promising microscopic model for nuclear dynamics at intermediate energies. The BL model goes beyond the much employed Boltzmann-Uehling-Uhlenbeck (BUU) model, and hence it provides a basis for describing dynamics of density fluctuations and addressing processes exhibiting spontaneous symmetry breaking and catastrophic transformations in nuclear collisions, such as induced fission and multifragmentation. In these standard models, the collision term is treated in a Markovian approximation by assuming that two-body collisions are local in both space and time, in accordance with Boltzmann`s original treatment. This simplification is usually justified by the fact that the duration of a two-body collision is short on the time scale characteristic of the macroscopic evolution of the system. As a result, transport properties of the collective motion has then a classical character. However, when the system possesses fast collective modes with characteristic energies that are not small in comparision with the temperature, then the quantum-statistical effects are important and the standard Markovian treatment is inadequate. In this case, it is necessary to improve the one-body transport model by including the memory effect due to the finite duration of two-body collisions. First we briefly describe the non-Markovian extension of the BL model by including the finite memory time associated with two-body collisions. Then, using this non-Markovian model in a linear response framework, we investigate the effect of the memory time on the agitation of unstable modes in nuclear matter in the spinodal zone, and calculate the collisional relaxation rates of nuclear collective vibrations.
Date: March 1, 1996
Creator: Ayik, S.
Partner: UNT Libraries Government Documents Department

Simplified simulation of Boltzmann-Langevin equation

Description: We briefly recall the Boltzmann-Langevin model of nuclear dynamics. We then summarize recent progress in deriving approximate analytical expressions for the associated transport coefficients and describe a numerical method for simulating the stochastic evolution of the phase-space density.
Date: June 1, 1994
Creator: Ayik, S. & Randrup, J.
Partner: UNT Libraries Government Documents Department