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Ternary particles with extreme N/Z ratios from neutron-induced fission

Description: The existing ternary fission models can well reproduce the yields of the most abundant light charged particles. However, these models tend to significantly overestimate the yields of ternary particles with an extreme N/Z ratio: {sup 3}He, {sup 11}Li, {sup 14}Be, etc. The experimental yields of these isotopes were investigated with the recoil separator LOHENGRIN down to a level of 10{sup {minus}10} per fission. Results from the fissioning systems {sup 233}U (n{sub th}, f), {sup 235}U(n{sub th},f), {sup 239}Pu(n{sub th},f) {sup 241}Pu(n{sub th},f) and {sup 245}Cm(n{sub th},f) are presented and the implications for the ternary fission models are discussed.
Date: May 16, 2000
Creator: Koster, U.; Faust, H.; Friedrichs, T.; Oberstedt, S.; Fioni, G.; Grob, M. et al.
Partner: UNT Libraries Government Documents Department

Baryon-baryon mixing in hypernuclei

Description: Implications of few-body hypernuclei for the understanding of the baryon-baryon interaction are examined. Octet-octet coupling effects not present in conventional, non strange nuclei are the focus. The need to identify strangeness {minus}2 hypernuclei to test model predictions is emphasized.
Date: May 1998
Creator: Gibson, B. F.
Partner: UNT Libraries Government Documents Department

Structure and dynamics of few-nucleon systems

Description: Few-nucleon physics is a field rich with high-quality experimental data and possibilities for accurate calculations of strongly-correlated quantum systems. In this article the authors discuss the traditional model of the nucleus as a system of interacting nucleons and outline many recent experimental results and theoretical developments in the field of few-nucleon physics. They present discussions of nuclear structure and spectra, clustering and correlations, elastic and inelastic electromagnetic form factors, low energy electroweak reactions, and nuclear scattering and response in the quasi-elastic regime. Through a review of the rich experimental data and a variety of theoretical developments, a coherent description of the nuclear strong and electroweak interaction properties emerges. In this article, they attempt to provide some insight into the practice and possibilities of in few-nucleon physics today.
Date: May 1, 1997
Creator: Schiavilla, R. & Carlson, J.
Partner: UNT Libraries Government Documents Department

Antiproton catalyzed fusion

Description: Because of the potential application to power production, it is important to investigate a wide range of possible means to achieve nuclear fusion, even those that may appear initially to be infeasible. In antiproton catalyzed fusion, the negative antiproton shields the repulsion between the positively charged nuclei of hydrogen isotopes, thus allowing a much higher level of penetration through the repulsive Coulomb barrier, and thereby greatly enhancing the fusion cross section. Because of their more compact wave function, the more massive antiprotons offer considerably more shielding than do negative muons. The effects of the shielding on fusion cross sections are most predominate, at low energies. If the antiproton could exist in the ground state with a nucleus for a sufficient time without annihilating, the fusion cross sections are so enhanced that at room temperature energies, values up to about 1,000 barns (that for d+t) would be possible. Unfortunately, the cross section for antiproton annihilation with the incoming nucleus is even higher. A model that provides an upper bound for the fusion to annihilation cross section for all relevant energies indicates that each antiproton will catalyze no more than about one fusion. Because the energy required to make one antiproton greatly exceeds the fusion energy that is released, this level of catalysis is far from adequate for power production.
Date: May 15, 1995
Creator: Morgan, D.L. Jr.; Perkins, L.J. & Haney, S.W.
Partner: UNT Libraries Government Documents Department

Improvements to the nuclear model code GNASH for cross section calculations at higher energies

Description: The nuclear model code GNASH, which in the past has been used predominantly for incident particle energies below 20 MeV, has been modified extensively for calculations at higher energies. The model extensions and improvements are described in this paper, and their significance is illustrated by comparing calculations with experimental data for incident energies up to 160 MeV.
Date: May 1, 1994
Creator: Young, P. G. & Chadwick, M. B.
Partner: UNT Libraries Government Documents Department

Investigation of the generation of several long-lived radionuclides of importance in fusion reactor technology: Report on a Coordinated Research Program sponsored by the International Atomic Energy Agency

Description: The IAEA initiated a Coordinated Research Program (CRP) in 1988 to obtain reliable information for 16 long-lived activation reactions of special importance to fusion reactor technology: {sup 27}Al (n, 2n){sup 26}Al, {sup 63}Cu(n,p){sup 63}Ni, {sup 94}Mo(n,p) {sup 94}Nb, {sup 109}Ag(n,2n){sup 108m}Ag, {sup 179}Hf(n,2n) {sup 178m2}Hf, {sup 182}W(n,n{sup `}a){sup 178m2}Hf, {sup 151}Eu(n,2n) {sup 150}gEu, {sup 153}Eu(n,2n){sup 152+m2}Eu, {sup 159}Tb(n, 2n){sup 158}Tb, {sup 158}Dy(n,p){sup 158}Tb, {sup 193}Ir(n,2n) {sup 192m2}Ir, {sup 187}Re(n,2n){sup 186m}Re, {sup 62}Ni(n{gamma}) {sup 63}Ni, {sup 98}Mo(n,{gamma}){sup 99}Mo({beta}-){sup 99}Tc, {sup 165}Ho(n,{gamma}) {sup 166m}Ho and {sup 191}Ir(n,{gamma}){sup 192m2}Ir. this paper documents progress achieved from the start of the program through mid- 1993.
Date: May 1, 1994
Creator: Smith, D. L. & Pashchenko, A. B.
Partner: UNT Libraries Government Documents Department

Engineering Physics and Mathematics Division progress report for period ending December 31, 1992

Description: In this report, our research is described through abstracts of journal articles, technical reports, and presentations organized into sections following the five major operating units in the division: Mathematical Sciences, Intelligent Systems, Nuclear Data and Measurement Analysis, Nuclear Analysis and Shielding, and the Engineering Physics Information Centers. Each section begins with an introduction highlighting honors, awards, and significant research accomplishments in that unit during the reporting period.
Date: May 1, 1993
Creator: Ward, R. C.
Partner: UNT Libraries Government Documents Department

Engineering Physics and Mathematics Division progress report for period ending December 31, 1992

Description: In this report, our research is described through abstracts of journal articles, technical reports, and presentations organized into sections following the five major operating units in the division: Mathematical Sciences, Intelligent Systems, Nuclear Data and Measurement Analysis, Nuclear Analysis and Shielding, and the Engineering Physics Information Centers. Each section begins with an introduction highlighting honors, awards, and significant research accomplishments in that unit during the reporting period.
Date: May 1, 1993
Creator: Ward, R.C.
Partner: UNT Libraries Government Documents Department

Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

Description: This document details activities during this reporting period topics discussed are: The first spectroscopic identification of the HCCCO and DCCCO radicals; detection of new vibrationally excited states of the carbon chain radicals CCH and CCD and the three-membered carbene ring, cyclopropenylidene; determination of an accurate structure of the cumulene carbene H{sub 2}CCC; analysis the hyperfine structure in the SiC radical; and the undertaking of a systematic search for new sulfur bearing radicals.
Date: May 1, 1992
Creator: Thaddeus, P. & Gottlieb, C.
Partner: UNT Libraries Government Documents Department

The trinucleons: Physical observables and model properties

Description: Our progress in understanding the properties of {sup 3}H and {sup 3}He in terms of a nonrelativistic Hamiltonian picture employing realistic nuclear forces is reviewed. Trinucleon model properties are summarized for a number of contemporary force models, and predictions for physical observables are presented. Disagreement between theoretical model results and experimental results are highlighted.
Date: May 1, 1992
Creator: Gibson, B. F.
Partner: UNT Libraries Government Documents Department

Saturating interactions in /sup 4/He with density dependence

Description: With the advent of larger and faster computers, as well as modern shell model codes, nuclear structure calculations for the light nuclei (A<16) which include full 2/bar h/..omega.. model spaces are quite feasible. However, there can be serious problems in the mixing of 2/bar h/..omega.. and higher excitations into the low-lying spectra if the effective interaction is non-saturating. Furthermore, effective interactions which are both saturating and density dependent have not generally been used in previous nuclear structure calculations. Therefore, we have undertaken studies of /sup 4/He using two-body potential interactions which incorporate both saturation and density-dependence. Encouraging initial results in remedying the mixing of 0 and 2/bar h/..omega.. excitations have been obtained. We have also considered the effects of our interaction on the /sup 4/He compressibility and the centroid of the breathing mode strength. First indications are that a saturating effective interaction, with a short-range density dependent part and a long-range density independent part, comes close to matching crude predictions for the compressibility of /sup 4/He. 11 refs., 6 tabs.
Date: May 3, 1989
Creator: Bloom, S.D.; Resler, D.A. & Moszkowski, S.A.
Partner: UNT Libraries Government Documents Department

An intercomparison of medium energy cross-section codes

Description: Five medium energy proton reaction cases are selected for benchmarking nuclear model codes. The quantities calculated are isotopic activation yields for 180 MeV protons on Al and 40-200 MeV protons on Co, and double differential neutron emission spectra from Al, Zr-90 and Pb-208 for 35, 80, 160, 318, and 800 presented consist of three types: a closed form preequilibrium plus evaporation model, an intranuclear-cascade and evaporation model, and a model relying on nuclear systematics. The characteristics of each code are described. There are orders of magnitude differences in the time for each type of code to calculate neutron emission spectra, with codes using systematics, preequilibrium and intranuclear-cascade models requiring seconds, minutes and hours, respectively. Calculations are not compared with experiment in this initial study. For double differential neutron emission spectra, there is good overall agreement in magnitude among the different types of codes at forward angles. Differences where they occur at forward angles are greatest for the mid-energy neutrons emitted. At back angles the incident energy at which the best overall agreement is obtained is 160 MeV and the material for which the best overall agreement is obtained is Al. 4 refs., 7 tabs.
Date: May 1, 1988
Creator: Pearlstein, S.
Partner: UNT Libraries Government Documents Department

The evaporative vector: Homogeneous systems

Description: Molecular beams of van der Waals molecules are the subject of much current research. Among the methods used to form these beams, three-sputtering, laser ablation, and the sonic nozzle expansion of neat gases - yield what are now recognized to be ''warm clusters.'' They contain enough internal energy to undergo a number of first-order processes, in particular that of evaporation. Because of this evaporation and its attendant cooling, the properties of such clusters are time-dependent. The states of matter which can be arrived at via an evaporative vector on a typical laboratory time-scale are discussed. Topics include the (1) temperatures, (2) metastability, (3) phase transitions, (4) kinetic energies of fragmentation, and (5) the expression of magical properties, all for evaporating homogeneous clusters.
Date: May 1, 1987
Creator: Klots, C.E.
Partner: UNT Libraries Government Documents Department

Lattice gauge theory as a nuclear many-body problem

Description: The conceptual connection between lattice quantum chromodynamics and a nuclear many-body problem is discussed. An illustrative example is given now the 0(3) nonlinear sigma model in (1 + 1) dimensions can be computered with a nuclear shell-model code with a speed which is competitive with other approaches. Progress toward the implementation of this technology in lattice SU(2) Yang-Mills gauge theory is described. 8 refs., 1 fig.
Date: May 1, 1986
Creator: Mathews, G.J.; Bloom, S.D. & Snyderman, N.J.
Partner: UNT Libraries Government Documents Department

Large-basis shell-model technology in nucleosynthesis and cosmology

Description: We discuss various applications of the Lanczos method to describe properties of many-body microscopic systems in nucleosynthesis and cosmology. These calculations include: solar neutrino detectors; beta-decay of excited nuclear states; electron-capture rates during a core-bounce supernova; exotic quarked nuclei as a catalyst for hydrogen burning; and the quark-hadron phase transition during the early universe. 27 refs., 3 figs.
Date: May 1, 1985
Creator: Mathews, G.J.; Bloom, S.D.; Takahashi, K.; Fuller, G.M. & Hausman, R.F. Jr.
Partner: UNT Libraries Government Documents Department

Dynamics of fission and heavy ion reactions

Description: Recent advances in a unified macroscopic-microscopic description of large-amplitude collective nuclear motion such as occurs in fission and heavy ion reactions are discussed. With the goal of finding observable quantities that depend upon the magnitude and mechanism of nuclear dissipation, one-body dissipation and two-body viscosity within the framework of a generalized Fokker-Planck equation for the time dependence of the distribution function in phase space of collective coordinates and momenta are considered. Proceeding in two separate directions, the generalized Hamilton equations of motion for the first moments of the distribution function with a new shape parametrization and other technical innovations are first solved. This yields the mean translational fission-fragment kinetic energy and mass of a third fragment that sometimes forms between the two end fragments, as well as the energy required for fusion in symmetric heavy-ion reactions and the mass transfer and capture cross section in asymmetric heavy-ion reactions. In a second direction, we specialize to an inverted-oscillator fission barrier and use Kramers' stationary solution to calculate the mean time from the saddle point to scission for a heavy-ion-induced fission reaction for which experimental information is becoming available. 25 references.
Date: May 1, 1984
Creator: Nix, J. R. & Sierk, A. J.
Partner: UNT Libraries Government Documents Department

New results on flavor production at PEP

Description: This report includes results from five PEP detectors: DELCO, HRS, MAC, MARK II and TPC. All, except the TPC, are presently taking data at PEP. The TPC is being upgraded: a new superconducting coil is being installed and other improvements are being implemented. The results discussed here are either new or improved since the Cornell Conference. New results on Particle Searches and a limit on neutrino generations are discussed. New data are included on weak couplings of c and b quarks. Various new results on hadron production are reported. All data were obtained in e/sup + -/ collisions with total energy ..sqrt..s=29 GeV. 54 references.
Date: May 1, 1984
Creator: Barbaro-Galtieri, A.
Partner: UNT Libraries Government Documents Department

Shell model study of /sup 90/ /sup 88/Zr

Description: Conventional spherical shell model calculations have been undertaken to describe /sup 90/Zr and /sup 88/Zr. Valence orbitals included the 1f/sub 5/2/, 2p/sub 3/2/, 2p/sub 1/2/, and lg/sub 9/2/ for protons, and lg/sub 9/2/ and 2d/sub 5/2/ for neutrons. For /sup 90/Zr, the number of lg/sub 9/2/ protons was less than or equal to 2. For the high spin even parity states of /sup 90/Zr, two calculations were performed, one with less than or equal to 4 (0) g/sub /9/2/ protons (neutron holes) and one with less than or equal to 2 (2) g/sub 9/2/ protons (neutron holes). For /sup 88/Zr, the number of particles in the g/sub 9/2/ shell was restricted to less than or equal to 10. For the high spin negative parity states, a calculation was done with up to 11 particles in the g/sub 9/2/ shell. A realistic two-body interaction was employed in this calculation. Predicted excitation energies are compared with experimental results, and for the lower lying positive parity states a comparison of electromagnetic transition rates is also made.
Date: May 1, 1984
Creator: Becker, J. A.; Bloom, S. D. & Warburton, E. K.
Partner: UNT Libraries Government Documents Department

4. pi. data of relativistic nuclear collisions. [Plastic ball]

Description: During the past two years, complete events of relativistic nuclear collisions are being studied with the Plastic Ball, the first electronic nonmagnetic particle-identifying 4..pi.. spectrometer. It is well suited to handle the large multiplicities in these reactions and allows collection of data at a rate sufficient to make further software selections to look at rare events. The analysis of the data follows various lines covering topics like thermalization, stopping or transparency, cluster-production mechanism (--can it tell entropy), search for collective flow through various global analyzing methods that allow determination of the scattering plane, projectile fragmentation (--is there a bounce-off), pion distribution, two-particle correlations: Hanbury-Brown Twiss, and excited nuclear states (--nucleosynthesis at the freezeout point or from chemical equilibrium). We will cover in this contribution only two subjects: stopping and thermalization and cluster production.
Date: May 1, 1983
Creator: Gutbrod, H.H.; Gustafsson, H.A. & Kolb, B.
Partner: UNT Libraries Government Documents Department

Pion production at 180/sup 0/ in nucleus-nucleus collisions

Description: A survey experiment of pion production at 180/sup 0/ in nucleus-nucleus collisions is presented. Beams of 1.05 GeV/A and 2.1 GeV/A protons, alphas, and carbon were used, as well as proton beams of 0.80 GeV, 3.5 GeV, and 4.89 GeV, and argon beams of 1.05 GeV/A and 1.83 GeV/A. This is the first such experiment to use the heavier beams. Targets used ranged from carbon to lead. An in-depth review of the literature, both experimental and theoretical, is also presented. The systematics of the data are discussed, and comparisons are made both with prior experiments and with the predictions of the models reviewed. The cross sections appear consistent with a simple single nucleon-nucleon collision picture, without the need for collective or other exotic effects. Suggestions for future work are made.
Date: May 1, 1983
Creator: Chessin, S.A.
Partner: UNT Libraries Government Documents Department

Ultra-relativistic heavy ions and cosmic rays

Description: The collisions of ultra-relativistic heavy ions, E/sub /N/ greater than or equal to 1 TeV/nucleon are most interesting, since, at these energies, matter is produced at sufficiently high energy density that a quark-gluon plasma has a good chance to form. Very heavy ions are also most interesting since the matter forms in a larger volume than for light ions, and the matter is at a somewhat higher energy density. At very high energies with very heavy ions there is great flexibility in the experimental signals which might be studied, as well as the nature of the matter which is produced. The fragmentation region and central region provide different environments where a plasma might form. The former is baryon rich while the central region is high temperature with low baryon number density and is not accessible except at very high energies.
Date: May 1, 1983
Creator: McLerran, L.
Partner: UNT Libraries Government Documents Department

Nuclear-deformation energies according to a liquid-drop model with a sharp surface

Description: We present an atlas of 665 deformation-energy maps and 150 maps of other properties of interest, relevant for nuclear systems idealized as uniformly charged drops endowed with a surface tension. The nuclear shapes are parametrized in terms of two spheres modified by a smoothly fitted quadratic surface of revolution and are specified by three variables: asymmetry, sphere separation, and a neck variable (that goes over into a fragment-deformation variable after scission). The maps and related tables should be useful for the study of macroscopic aspects of nuclear fission and of collisions between any two nuclei in the periodic table.
Date: May 1, 1982
Creator: Blocki, J. & Swiatecki, W.J.
Partner: UNT Libraries Government Documents Department