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Application of the Resonating Hartree-Fock Theory to the Lipkin Model

Description: In order to make clear essential features of the resonating Hartree-Fock (Res HF) theory for a Fermion system with large quantum fluctuations and to show its superiority over the usual HF theory, the authors apply it to the exactly solvable Lipkin model. They use a new direct optimization algorithm to optimize orbitals in nonorthogonal Slater determinants (S-dets) in a Res HF wave function. For the sake of simplicity, they assume a Res HF wave function to be superposed by two S-dets {vert_bar}g{sub 1}> {vert_bar}g{sub 2}> which give corresponding two local energy minima of monopole deformation. They make the self-consistent Res HF calculation so as to minimize the energy functional including up to the second order variation. The Res HF ground state generated with only two S-dets brings the ground state energy very near to the exact one and then explains most of the ground state correlation energy.
Date: December 31, 1993
Creator: Nishiyama, Seiya
Partner: UNT Libraries Government Documents Department

Few-body hypernuclear constraints

Description: Since the discovery of the first hyperfragment in a balloon flown emulsion stack some two score years ago, physicists have worked to understand how the addition of the strangeness degree of freedom alters the picture of nuclei and the baryon-baryon force. Because the {Lambda} and {Sigma} masses differ markedly from that of the proton and neutron, SU (3) symmetry is broken. How it is broken is a question of importance to the fundamental understanding of the baryon-baryon interaction. New dynamical symmetries, forbidden by the Pauli principle in conventional nuclei, appear. Three-body forces play a more significant role. A binding anomaly in A {equals} 5 as well as a possible spin inversion between ground and excited states in A {equals} 4 appear. Surprisingly narrow structure near the threshold for {Sigma} production has been reported in the {sup 4}He (K{sup {minus}}, {pi}{sup {minus}}) spectrum while no corresponding structure is observed in the companion {sup 4}He(K{sup {minus}}, {pi}{sup +}) spectrum; this has been interpreted as evidence for a {sub {Sigma}}{sup 4}He bound state. Finally, the reported observation of {Lambda}{Lambda}-hypernuclei, in particular {sub {Lambda}{Lambda}}{sup 6}He, bears directly upon the possibilities for the prediction of a bound H particle--the S {equals} {minus}2 dibaryon. Although it is not feasible to invert the analysis and determine the interaction from the data on few-body systems, it is possible to utilize these data to constrain the models, provided one is careful. The author will explore briefly the constraints which the few-body data impose and the level of understanding that has been achieved.
Date: December 31, 1993
Creator: Gibson, B. F.
Partner: UNT Libraries Government Documents Department

Insights into nuclear structure and the fission process from spontaneous fission

Description: The {gamma}-rays emitted following spontaneous and induced fission are rich sources of information about the structure of neutron-rich nuclei and about the fission process itself. The study of spontaneous fissioning isotopes with large Ge detector arrays are providing a wealth of such information as seen, for example, in recent reports. In this paper we present some of our most recent results on nuclear structure studies and conclusions on the fission process itself. In our work, we have employed in spontaneous fission, a triple gamma coincidence study for the first time and a high resolution, X-ray detector-{gamma}-coincidence study. These data provide powerful ways of separating the gamma rays which belong to a particular nucleus. The triple coincidence technique was used to uniquely identify the levels in {sup 136}Te and higher spin states in its N=84 isotones, {sup 138}Xe and {sup 140}Ba{sup 171}. Some other examples of the level structures observed in the low and high mass partners are presented, including a detailed analysis of the backbending of the moment of inertia in {sup 112,114,116}Pd. Finally, we present the first examples of how our analysis allows one to extract a detailed picture of the dependence of the angular momentum on the mass and atomic numbers of the fission fragments and of the long-sought neutron multiplicity distribution from zero-n to ten-n as a function of the charge and mass asymmetry.
Date: December 31, 1993
Creator: Hamilton, J.H.; Butler-Moore, K. & Ramayya, A.V.
Partner: UNT Libraries Government Documents Department

Experimental and theoretical nuclear data work at ORELA

Description: The Oak Ridge Electron Linear Accelerator (ORELA) passed the 100,000 hours of operation milestone in October, 1992, and continues to operate as an intense, pulsed neutron source. In addition to performing measurements of interest to applied and basic research, they are involved in international nuclear data evaluation activities, as well as nuclear model code development. The intense, slow-positron source attached to ORELA continues to attract interest from industry, and a new photon activation facility added this last year is also being used for basic research and by industry. The author describes some of the above activities.
Date: December 1, 1993
Creator: Larson, D. C.
Partner: UNT Libraries Government Documents Department

Equilibration and multifragmentation in heavy ion reactions

Description: Modeling of multifragmentation measurements from heavy ion reactions generally requires separate treatment of the initial fast part of the reaction, during which energetic nucleons are emitted, and of a quasi-equilibrated system where sufficient degrees of freedom have been excited, so that statistical approaches may be applied. Some of the more sophisticated fast cascade models, e.g., Quantum molecular dynamics (QMD), might also produce fragment yields, however, transport models have not yet been able to satisfactorily reproduce fragmentation properties of nuclear reactions. In this work we consider the interactions of {sup 36}Ar with {sup 197}Au at incident energies of 35 to 110 MeV{center_dot}A, which was investigated by de Souza et al. We will first look at two dynamic models which may be used to estimate the excitation remaining for quasi-equilibrated systems following the fast nucleonic cascade, specifically the Boltzmann master equation (BME) and Quantum molecular dynamics (QMD) approaches. Using excitations from the BME model to estimate values for quasi-equilibrated nuclei, we will explore two approaches to statistical multifragmentation calculations, one of sequential binary decay, the other a simultaneous multifragmentation model (SMM). We will consider central collisions in our calculations, and experimental results gated on the highest total charged particle emissions -- those deduced to be central collisions.
Date: September 1, 1993
Creator: Peilert, G.; Mustafa, M. G.; Blann, M. & Botvina, A.
Partner: UNT Libraries Government Documents Department

Investigation of the relative abundance of heavy versus light nuclei in primary cosmic rays using underground muon bundles

Description: We study multiple muon events (muon bundles) recorded underground at a depth of 2090 mwe. To penetrate to this depth, the muons must have energies above 0.8 TeV at the Earth`s surface; the primary cosmic ray nuclei which give rise to the observed muon bundles have energies at incidence upon the upper atmosphere of 10 to 10{sup 5}TeV. The events are detected using the Soudan 2 experiment`s fine grained tracking calorimeter which is surrounded by a 14 m {times}10 m {times} 31 m proportional tube array (the ``active shield``). Muon bundles which have at least one muon traversing the calorimeter, are reconstructed using tracks in the calorimeter together with hit patterns in the proportional tube shield. All ionization pulses are required to be coincident within 3 microseconds. A goal of this study is to investigate the relative nuclear abundances in the primary cosmic radiation around the ``knee`` region (10{sup 3} {minus} 10{sup 4} TeV) of the incident energy spectrum. Four models for the nuclear composition of cosmic rays are considered: The Linsley model, the Constant Mass Composition model (CMC), the Maryland model and the Proton-poor model. A Monte Carlo which incorporates one model at a time is used to simulate events which are then reconstructed using the same computer algorithms that are used for the data. Identical cuts and selections are applied to the data and to the simulated events.
Date: June 8, 1993
Creator: Sundaralingam, N.
Partner: UNT Libraries Government Documents Department

Electromagnetic studies of nucleon and nuclear structure

Description: Important objectives of the group are the study of subatomic structure through experimental measurements and the interpretation of the data through modeling. The common theme that unifies the studies of strong interactions and hadronic systems is the effort to determine the electromagnetic response as completely as possible. The general approach is coincidence detection of exclusive final states and determination of the dependence on the spin variables using polarized beams and targets and outgoing nucleon polarimetry. Direct reaction and giant resonance studies of electron quasi-elastic scattering on {sup 12}C and {sup 16}O are reported, as well as work on nuclear structure models and instrumentation development.
Date: June 1, 1993
Creator: Heisenberg, J. H.; Calarco, J. R.; Hersman, F. W. & Dawson, J. F.
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

Nuclear structure models: Applications and development. [Department of Physics, Tennessee Technological University, Cookeville, Tennessee]

Description: This report summarizes the progress made during the period July 1, 1992 to April 30, 1993. The study of rotational structure at moderate spins in odd-odd nuclei (Section 1) has continued into the A [approximately] 80 region. Recent experimental data for the positive parity band in [sup 82]Y, including absolute BM1 and BE2 values, are rather well described with a prolatish'' triaxial shape and a [pi]g[sub 9/2] [direct product] [nu]g[sub 9/2] configuration. Little effect from a protonneutron interaction has been found so far. Current studies of odd mass nuclei (Section 2) are mainly focussing on low spin, low energy states in the A [approximately] 130 region as a probe to the evolving collectivity. These projects involve direct collaboration with experimental colleagues. Finally, a view of the microscopic foundation of particle-core coupling models approached from the equation of motion method is presented (Section 3).
Date: April 1, 1993
Creator: Semmes, P.B.
Partner: UNT Libraries Government Documents Department

Fluid dynamical predictions for Au+Au collisions at AGS

Description: Signatures of collective effects are studied in the Quark Gluon String Model and in the Fluid Dynamical Model for Au {plus} Au collisions at 11.6 A GeV. In the fluid dynamical model the dependence of measurables on the QGP formation in the EOS is pointed out, although the max. total amount of pure QGP formed is only 4 fm{sup 3} in these reactions. In QGSM the lifetime and extent of latent energy in strings is studied.
Date: February 1, 1993
Creator: Bravina, L.; Csernai, L. P.; Levai, P. & Strottmam, D.
Partner: UNT Libraries Government Documents Department

Cross section of electron - off-shell nucleon interaction

Description: The results of theoretical calculations of the electron-bound nucleon interaction cross section ({sigma}{sub eN}) are given for four theoretical approaches. It is shown that there are significant differences between predictions of these methods, especially for the deeply bound (high internal momentum, high removing energy) nucleons. To test these predictions experimentally the authors study of cross sections obtained for two primary energies or for bound proton and neutron. These ratios will be insensitive to the nuclear spectral function as well as to the off-shell modifications of the bound nucleon form-factors if every pair of measurements are made for the same values of energy and momentum-transfers, removal energy, internal and final momenta of the struke nucleon. It is shown that dependences of the discussed ratios on various kinematical parameters are significantly different in different approaches and can be used to distinguish the theoretical models used.
Date: January 1, 1993
Creator: Egiyan, K. & Sargsyan, M.
Partner: UNT Libraries Government Documents Department

Fluid dynamical predictions for Au+Au collisions at AGS

Description: Signatures of collective effects are studied in the Quark Gluon String Model and in the Fluid Dynamical Model for Au [plus] Au collisions at 11.6 A GeV. In the fluid dynamical model the dependence of measurables on the QGP formation in the EOS is pointed out, although the max. total amount of pure QGP formed is only 4 fm[sup 3] in these reactions. In QGSM the lifetime and extent of latent energy in strings is studied.
Date: January 1, 1993
Creator: Bravina, L.; Csernai, L.P. (Bergen Univ. (Norway). Dept. of Physics); Levai, P. (Bergen Univ. (Norway). Dept. of Physics Hungarian Academy of Sciences, Budapest (Hungary). Central Research Inst. for Physics) & Strottmam, D. (Los Alamos National Lab., NM (United States))
Partner: UNT Libraries Government Documents Department