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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

Nuclear data for radiotherapy: Presentation of a new ICRU report and IAEA initiatives

Description: An ICRU report entitled ''Nuclear Data for neutron and Proton Radiotherapy and for Radiation Protection'' is in preparation. The present paper presents an overview of this report, along with examples of some of the results obtained for evaluated nuclear cross sections and kerma coefficients. These cross sections are evaluated using a combination of measured data and the GNASH nuclear model code for elements of importance for biological, dosimetric, beam modification and shielding purposes. In the case of hydrogen both R-matrix and phase-shift scattering theories are used. In the report neutron cross sections and kerma coefficients will be presented up to 100 MeV and proton cross sections up to 250 MeV. An IAEA Consultants' Meeting was also convened to examine the ''Status of Nuclear Data needed for Radiation Therapy and Existing Data Development Activities in Member States''. Recommendations were made regarding future endeavors.
Date: September 1, 1998
Creator: Chadwick, M.B.; Jones, D.T.L. & Barschall, H.H.
Partner: UNT Libraries Government Documents Department

Global economics/energy/environmental (E{sup 3}) modeling of long-term nuclear energy futures

Description: A global energy, economics, environment (E{sup 3}) model has been adopted and modified with a simplified, but comprehensive and multi-regional, nuclear energy module. Using this model, consistent nuclear energy scenarios are constructed. A spectrum of future is examined at two levels in a hierarchy of scenario attributes in which drivers are either external or internal to nuclear energy. Impacts of a range of nuclear fuel-cycle scenarios are reflected back to the higher-level scenario attributes. An emphasis is placed on nuclear materials inventories (in magnitude, location, and form) and their contribution to the long-term sustainability of nuclear energy and the future competitiveness of both conventional and advanced nuclear reactors.
Date: September 1, 1997
Creator: Krakowski, R.A.; Davidson, J.W.; Bathke, C.G.; Arthur, E.D. & Wagner, R.L. Jr.
Partner: UNT Libraries Government Documents Department

Additional degrees of freedom in skyrmion motion

Description: The authors consider the quantization of chiral solitons with baryon number B > 1. Classical solitons are obtained within the framework of a variational approach. From the form of the soliton solution it can be seen that besides the group of symmetry describing transformations of the configuration as a whole there are additional symmetries corresponding to internal transformations. Taking into account the additional degrees of freedom leads to some sort of spin alignment for light nuclei and gives constraints on their spectra.
Date: September 1, 1994
Creator: Musatov, I.; Nikolaev, V. & Tkachev, O.
Partner: UNT Libraries Government Documents Department

The dynamics of fragment formation

Description: We demonstrate that in the Quantum Molecular Dynamics model, dynamical correlations can result in the production rate for final state nucleon clusters (and hence composite fragments) being higher than would be expected if statistics and the available phase space were dominant in determining composite formation. An intranuclear cascade or a Boltzmann-Uehling-Uhlenbeck model, combined with a statistical approach in the late stage of the collision to determine composites, provides an equivalent description only under limited conditions of centrality and beam energy. We use data on participant fragment production in Au + Au collisions in the Bevalac`s BOS time projection chamber to map out the parameter space where statistical clustering provides a good description. In particular, we investigate momentum-space densities of fragments up to {sup 4}He as a function of fragment transverse momentum, azimuth relative to the reaction plane, rapidity, multiplicity and beam energy.
Date: September 1, 1994
Creator: Keane, D. & Collaboration, EOS
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

Nuclear structure studies at intermediate energy. [School of Physics and Astronomy, Univ. of Minnesota]

Description: New experimental results are given for proton elastic and inelastic cross sections for [sup 182,186]W at 650 MeV, [sup 208]Pb and [sup 60]Ni(p,t) cross sections at 120 MeV, a coincidence study of the [sup 40]Ca([rvec p],2p) reaction. In addition to the above, data reduction and analysis are also being carried out as follows: global analysis of [sup 28]Si and [sup 58]Ni([rvec p],p[prime]) data at 135, 178, 333, 500, and 800 MeV for high-spin stretched states using medium modified interactions (conventional and QCD effective mass modifications); analysis of [sup 206,207,208]Pb([rvec p],p) elastic data at 650 MeV. Work on development of techniques to study relativistic effects of proton[endash]nucleus scattering at forward angles and extended angular range of S[sub nn] measurements in [sup 40]Ca was also carried out.
Date: September 1, 1992
Creator: Hintz, N.M.; Sethi, A.; Starodubsky, V.; Yang, Xin hua; Franey, M. & Mihaildis, D.
Partner: UNT Libraries Government Documents Department

Nuclear structure from radioactive decay

Description: This report discusses nuclear structure from radioactive decay of the following: Neutron-Deficient Iridium Isotopes; Neutron-Deficient Platinum Isotopes; Neutron-Deficient Gold Isotopes; Neutron-Deficient Mercury Isotopes; Neutron-Deficient Thallium Isotopes; Neutron-Deficient Lead Isotopes; Neutron-Deficient Samarium Isotopes; Neutron-Deficient Promethium Isotopes; Neutron-Deficient Neodymium Isotopes; and Neutron-Deficient Praseodymium Isotopes. Also discussed are Nuclear Systematics and Models.
Date: September 30, 1991
Creator: Wood, J.L.
Partner: UNT Libraries Government Documents Department

Nuclear structure from radioactive decay. Annual progress report

Description: This report discusses nuclear structure from radioactive decay of the following: Neutron-Deficient Iridium Isotopes; Neutron-Deficient Platinum Isotopes; Neutron-Deficient Gold Isotopes; Neutron-Deficient Mercury Isotopes; Neutron-Deficient Thallium Isotopes; Neutron-Deficient Lead Isotopes; Neutron-Deficient Samarium Isotopes; Neutron-Deficient Promethium Isotopes; Neutron-Deficient Neodymium Isotopes; and Neutron-Deficient Praseodymium Isotopes. Also discussed are Nuclear Systematics and Models.
Date: September 30, 1991
Creator: Wood, J. L.
Partner: UNT Libraries Government Documents Department

A review of nuclear data needs and their status for fusion reactor technology with some suggestions on a strategy to satisfy the requirements

Description: A review was performed on the needs and status of nuclear data for fusion-reactor technology. Generally, the status of nuclear data for fusion has been improved during the past two decades due to the dedicated effort of the nuclear data developers. However, there are still deficiencies in the nuclear data base, particularly in the areas of activation and neutron scattering cross sections. Activation cross sections were found to be unsatisfactory in 83 of the 153 reactions reviewed. The scattering cross sections for fluorine and boron will need to be improved at energies above 1 MeV. Suggestions concerning a strategy to address the specific fusion nuclear data needs for dosimetry and activation are also provided.
Date: September 1, 1991
Creator: Smith, D.L. (Argonne National Lab., IL (United States)) & Cheng, E.T. (TSI Research, Inc., Solana Beach, CA (United States))
Partner: UNT Libraries Government Documents Department

A review of nuclear data needs and their status for fusion reactor technology with some suggestions on a strategy to satisfy the requirements

Description: A review was performed on the needs and status of nuclear data for fusion-reactor technology. Generally, the status of nuclear data for fusion has been improved during the past two decades due to the dedicated effort of the nuclear data developers. However, there are still deficiencies in the nuclear data base, particularly in the areas of activation and neutron scattering cross sections. Activation cross sections were found to be unsatisfactory in 83 of the 153 reactions reviewed. The scattering cross sections for fluorine and boron will need to be improved at energies above 1 MeV. Suggestions concerning a strategy to address the specific fusion nuclear data needs for dosimetry and activation are also provided.
Date: September 1, 1991
Creator: Smith, D. L. & Cheng, E. T.
Partner: UNT Libraries Government Documents Department

Nuclear Structure From Radioactive Decay

Description: This report discusses the nuclear structure of the following isotopes as a result of radioactive decays: neutron-deficient iridium isotopes; neutron-deficient platinum isotopes; neutron-deficient gold isotopes; neutron-deficient mercury isotopes; neutron-deficient thallium isotopes; neutron-deficient lead isotopes; neutron-deficient promethium isotopes; and neutron-deficient samarium isotopes.
Date: September 30, 1990
Creator: Wood, J. L.
Partner: UNT Libraries Government Documents Department

Beta-delayed proton emission in neutron-deficient lanthanide isotopes

Description: Forty-two ..beta..-delayed proton precursors with 56less than or equal toZless than or equal to71 and 63less than or equal toNless than or equal to83 were produced in heavy-ion reactions at the Lawrence Berkeley Laboratory SuperHILAC and their radioactive decay properties studied at the on-line mass separation facility OASIS. Twenty-five isotopes and eight delayed proton branches were identified for the first time. Delayed proton energy spectra and proton coincident ..gamma..-ray and x-ray spectra were measured for all precursors. In a few cases, proton branching ratios were also determined. The precursor mass numbers were determined by the separator, while the proton coincident x-ray energies provided unambiguous Z identifications. The proton coincident ..gamma..-ray intensities were used to extract final state branching ratios. Proton emission from ground and isomeric states was observed in many cases. The majority of the delayed proton spectra exhibited the smooth bell-shaped distribution expected for heavy mass precursors. The experimental results were compared to statistical model calculations using standard parameter sets. Calculations using Nilsson model/RPA ..beta..-strength functions were found to reproduce the spectral shapes and branching ratios better than calculations using either constant or gross theory ..beta..-strength functions. Precursor half-life predictions from the Nilsson model/RPA ..beta..-strength functions were also in better agreement with the measured half-lives than were gross theory predictions. The ratios of positron coincident proton intensities to total proton intensities were used to determine Q/sub EC/-B/sub p/ values for several precursors near N=82. The statistical model calculations were not able to reproduce the experimental results for N=81 precursors. 154 refs., 82 figs., 19 tabs.
Date: September 30, 1988
Creator: Wilmarth, P.A.
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

Beta-delayed proton decay in the lanthanide region

Description: A total of 24 new ..beta..-delayed proton precursors and several new decay branches in the region of 56 < Z < 72 and N < 82 have been identified with the OASIS on-line mass separator facility at the SuperHILAC in Berkeley. Proton spectra and halflives were measured for all precursors. Additional properties determined for many of the isotopes include spins and parities of the precursors, final state feedings, proton branching ratios, (Q/sub EC/-S/sub p/) energy differences, and new levels in the proton decay daughters. Mixed ..beta..-delayed proton decay from precursor isomers and ground states has been observed. The proton decay has been compared to statistical model calculations using Gamow-Teller (GT) ..beta..-strength functions obtained from RPA calculations with Nilsson model wave functions. For the N = 81 precursors /sup 151/Yb, /sup 149/Er, and /sup 147/Dy, pronounced structure in the proton spectra has been observed. An interpretation of this structure in the framework of ''doorway'' states is proposed. 25 refs., 6 figs., 1 tab.
Date: September 1, 1987
Creator: Nitschke, J.M.; Wilmarth, P.A.; Gilat, J.; Moeller, P. & Toth, K.S.
Partner: UNT Libraries Government Documents Department

New nuclear structure calculations and the astrophysical r-process

Description: Recent developments in nuclear-structure calculations used to calculate the nuclear properties of neutron-rich heavy elements can have a dramatic effect on astrophysical r-process calculations. In particular, in the context of the macroscopic-microscopic method, studies of the effect of the finite range of the nuclear force on the surface energy, the shape dependence of the Wigner term, new shape degrees of freedom near scission, and improved single particle potentials for neutron-rich heavy elements have led to improved calculations of the properties of heavy elements. We will discuss preliminary applications of these new models to nuclei of interest in the astrophysical r-process and the implications for nuclear cosmochronology and the existence of superheavy elements in nature. 14 refs., 6 figs.
Date: September 1, 1987
Creator: Howard, W.M.; Moeller, P.; Mathews, G.J. & Meyer, B.S.
Partner: UNT Libraries Government Documents Department

Oblate-prolate shape competition in Z = 34 to 38 nuclei

Description: Now magic numbers for deformed shapes are established at N and Z of 38 and N of 60. These shell gaps at large deformation (..beta.. approx. = 0.4) are magic when the proton and neutron shell gaps reinforce each other. Other shell gaps for 34 and 36 are predicted to be important for oblate deformation. The competition between these oblate and the 38 prolate gaps as well as the 40 spherical shell gap are considered. In /sup 71/Se coexistence of oblate (..beta.. approx. = -0.24) and large prolate (..beta.. approx. = 0.4) shapes are observed. In /sup 72/Se the excited prolate band with large deformation which coexists with the near-spherical ground state is found to dominate the yrast spectrum to 28/sup +/. The moment of inertia of this band is essentially that of a rigid body. This moment of inertia supports the suggestion that the ''super deformation'', ..beta.. approx. = 0.4, being observed in this region may be associated with a collapse of pairing.
Date: September 1, 1987
Creator: Hamilton, J.H.; Ramayya, A.V.; Zhao, X.; Maguire, C.F.; Ma, W.C.; KormickI, J. et al.
Partner: UNT Libraries Government Documents Department

Nuclear de-excitation processes following medium energy heavy ion collisions

Description: As heavy ion reaction studies have progressed from beam energies below 10 MeV/nucleon to higher energies, many non-equilibrium reaction phenomena have been observed. Among these are nucleon emission with velocities in excess of the beam velocity, incomplete momentum transfer to evaporation residue and fission-like fragments, ..gamma..-rays with energies in excess of 100 MeV, and ..pi../sup 0/ production when beam energies are below the threshold for production by the nucleon-nucleon collision mechanism. Additionally, prefission neutrons have been observed in excess of numbers expected from equilibrium models. A few of the approaches which have been applied to these phenomena are as follows: Intranuclear cascade: two body collisions are assumed to mediate the equilibration. The geometry and momentum space is followed semiclassically. The approach has many successes though it may suffer in a few applications is not following holes; TDHF considers one body processes only; in the energy regime of interest, two body processes are important so that this may not be a viable approach; Boltzmann-Uehling-Uhlenbeck or Vlasov-Uehling-Uhlenbeck (BUU/VUU) equations combine both one body and two body dynamics. The spatial and momentum evolution of the reactions are followed in a mean field. These should be the Cadillacs of the models. They are computationally tedious, and sometimes significant approximations are made in order to achieve computational tract ability; models of collective deceleration. A very simple model approach is discussed to interpret these phenomena, the Boltzmann master equation (BME). The hybrid model was the first to be applied to the question of heavy ion precompound decay, and the BME second. 26 refs., 5 figs., 2 tabs.
Date: September 1, 1986
Creator: Blann, M.
Partner: UNT Libraries Government Documents Department

Single particle effects in precompound decay reactions

Description: Precompound decay models generally rely on use of a partial state density (PSD) formula which is generated using an assumed equidistantly spaced set of single particle levels. This is a reasonable assumption for mid-shell nuclei; however it has been demonstrated that quite large errors may be introduced by making the equidistant spacing assumption for nuclei which have neutron or proton numbers near or at major shell closures. This work reviews the simple qualitative considerations of those deviations expected for near closed shell nuclei, these expectations are compared with experimental results, and steps are taken to implement use of partial state densities calculated with more realistic sets of single particle levels in precompound decay calculations. This is done for the case of Zr targets. 13 refs., 14 figs.
Date: September 1, 1986
Creator: Blann, M.; Komoto, T.; Reffo, G.; Fabbri, F. & Grimes, S.M.
Partner: UNT Libraries Government Documents Department

Shell model calculations of /sup 90,88/Zr and /sup 90,88/Y

Description: Conventional spherical shell model calculations have been undertaken to describe /sup 90,88/Zr and /sup 90,88/Y. In these large scale calculations valence orbitals included 1f/sub 5/2/,2p/sub 3/2/,2p/sub 1/2/, and 1g/sub 9/2/. The d/sub 5/2/ orbital was included for /sup 90/Y and for high-spin calculations in /sup 90/Zr. Restrictions were placed on orbital occupancy so that the basis set amounted to less than 25,000 Slater determinants. Calculations were done with a local, state independent, two-body interaction with single Yukawa form factor. Predicted excitation energies and electromagnetic transition rates are compared with recent experimental results. 6 refs., 2 figs.
Date: September 3, 1985
Creator: Becker, J.A. & Bloom, S.D.
Partner: UNT Libraries Government Documents Department

Trends in the study of light proton rich nuclei

Description: Recent work in light proton-rich nuclei is reviewed. Evidence for the first T/sub z/ = -5/2 nuclide, /sup 35/Ca, is presented. The mechanisms of two-proton emission following beta-decay is investigated. Future directions in this field are discussed. 23 refs., 5 figs. (WRF)
Date: September 1, 1985
Creator: Moltz, D.M.; Aysto, J.; Hotchkis, M.A.C. & Cerny, J.
Partner: UNT Libraries Government Documents Department

Microscopic calculation for deformed nuclei

Description: The microscopic basis of the Interacting Boson Model for deformed nuclei is discussed. The IBM Hamiltonian is constructed microscopically in the following two steps. In the first step, the collective nucleon pairs of J = 0/sup +/ (S), 2/sup +/ (D), etc. are mapped onto the corresponding bosons. Nucleon-nucleon interactions are also mapped onto boson-boson interactions. This mapping method for deformed nuclei was proposed recently, and it turned out that this method is consistent with the Hartree-Fock-Bogoliubov + angular momentum projection calculation. Low-lying collective states primarily consist of S and D pairs. Consequently, the corresponding boson states mainly consist of s and d bosons, while there are some admixture of g-bosons. In the second step, effects of these g-bosons are included within the s-d boson space by a unitary transformation which transforms a combination of d and g bosons into a new d-boson. By minimizing the coupling between new d and g bosons with an appropriate mixing angle, one can neglect the coupling and obtain the IBM Hamiltonian with s and d bosons. It is demonstrated that the s-d Hamiltonian thus derived indeed reproduces spectra of the original s-d-g Hamiltonian.
Date: September 24, 1984
Creator: Otsuka, Takaharu
Partner: UNT Libraries Government Documents Department

Modeling level structures of odd-odd deformed nuclei

Description: A technique for modeling quasiparticle excitation energies and rotational parameters in odd-odd deformed nuclei has been applied to actinide species where new experimental data have been obtained by use of neutron-capture gamma-ray spectroscopy. The input parameters required for the calculation were derived from empirical data on single-particle excitations in neighboring odd-mass nuclei. Calculated configuration-specific values for the Gallagher-Moszkowski splittings were used. Calculated and experimental level structures for /sup 238/Np, /sup 244/Am, and /sup 250/Bk are compared, as well as those for several nuclei in the rare-earth region. The agreement for the actinide species is excellent, with bandhead energies deviating 22 keV and rotational parameters 5%, on the average. Corresponding average deviations for five rare-earth nuclei are 47 keV and 7%. Several applications of this modeling technique are discussed. 18 refs., 5 figs., 4 tabs.
Date: September 7, 1984
Creator: Hoff, R.W.; Kern, J.; Piepenbring, R. & Boisson, J.P.
Partner: UNT Libraries Government Documents Department