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Results from the First {sup 249}Cf + {sup 48}Ca Experiment

Description: The present paper reports the results of an attempt aimed at the synthesis of element 118 in the reaction {sup 249}Cf({sup 48}Ca,3n){sup 294}118. The experiment was performed employing the Dubna Gas-filled Recoil Separator and the U400 heavy-ion cyclotron at FLNR, JINR, Dubna. In the course of a 2300-hour irradiation of an enriched {sup 249}Cf target (0.23 mg/cm{sup 2}) with a beam of 245-MeV {sup 48}Ca ions, we accumulated a total beam dose of 2.5 x 10{sup 19} ions. We detected two events that may be attributed to the formation and decay of nuclei with Z=118. For one event, we observed a decay chain of two correlated {alpha}-decays with corresponding energies and correlation times of E{sub {alpha}1} = 11.65 {+-} 0.06 MeV, t{sub {alpha}1} = 2.55 ms and E{sub {alpha}2} = 10.71 {+-} 0.17 MeV, t{sub {alpha}2} = 42.1 ms and, finally, a spontaneous fission with the sum of the kinetic energies of the fission fragments E{sub tot} = 207 MeV (TKE {approx} 230 MeV) and t{sub SF} = 0.52 s. In the second event chain, the recoil nucleus decayed into two fission fragments with E{sub tot} = 223 MeV (TKE {approx} 245 MeV) 3.16 ms later, without intervening {alpha} decays. The probabilities that these events were caused by the chance correlations of unrelated signals are negligible. Both events were observed at an excitation energy of the compound nucleus {sup 297}118 of E* = 30.0 {+-} 2.4 MeV, close to the expected maximum of the 3n-evaporation channel. The relationship between the decay energy Q{sub {alpha}} and decay period T{sub {alpha}} shows that sequential {alpha}-transitions in the first event correspond to the decay chain with Z = 118{_}116{_}114. Decay characteristics of the newly observed nuclides are compared with radioactive decay properties of the even-even isotopes with Z = 116, 114 and 112 ...
Date: February 3, 2003
Creator: Oganessian, Y T; Utyonkov, V K; Lobanov, Y V; Abdullin, F S; Polyakov, A N; Shirokovsky, I V et al.
Partner: UNT Libraries Government Documents Department

Experimental test of nuclear magnetization distribution and nuclear structure models

Description: Models exist that ascribe the nuclear magnetic fields to the presence of a single nucleon whose spin is not neutralized by pairing it up with that of another nucleon; other models assume that the generation of the magnetic field is shared among some or all nucleons throughout the nucleus. All models predict the same magnetic field external to the nucleus since this is an anchor provided by experiments. The models differ, however, in their predictions of the magnetic field arrangement within the nucleus for which no data exist. The only way to distinguish which model gives the correct description of the nucleus would be to use a probe inserted into the nucleus. The goal of our project was to develop exactly such a probe and to use it to measure fundamental nuclear quantities that have eluded experimental scrutiny. The need for accurately knowing such quantities extends far beyond nuclear physics and has ramifications in parity violation experiments on atomic traps and the testing of the standard model in elementary particle physics. Unlike scattering experiments that employ streams of free particles, our technique to probe the internal magnetic field distribution of the nucleus rests on using a single bound electron. Quantum mechanics shows that an electron in the innermost orbital surrounding the nucleus constantly dives into the nucleus and thus samples the fields that exist inside. This sampling of the nucleus usually results in only minute shifts in the electron´┐Ż s average orbital, which would be difficult to detect. By studying two particular energy states of the electron, we can, however, dramatically enhance the effects of the distribution of the magnetic fields in the nucleus. In fact about 2% of the energy difference between the two states, dubbed the hyperfine splitting, is determined by the effects related to the distribution of ...
Date: February 26, 1999
Creator: Beirsdorfer, P; Crespo-Lopez-Urrutia, J R & Utter, S B
Partner: UNT Libraries Government Documents Department

Measurement of the deuteron elastic structure functions up to large momentum transfers

Description: The cross section for elastic electron-deuteron scattering was measured in JLab experiment 91-026. The deuteron elastic structure functions A(Q{sup 2}) and B(Q{sup 2}) have been extracted from this data. The final results for the ``electric'' structure function A(Q{sup 2}), in the range of 0.7 less than or equal to Q{sup 2} less than or equal to 6.0 (GeV/c){sup 2} are presented. Preliminary results for the ``magnetic'' structure function B(Q{sup 2}) are presented in the range of 0.7 less than or equal to Q{sup 2} less than or equal to 1.35 (GeV/c){sup 2}. These data are compared with theoretical predictions of both meson-nucleon and quark-gluon based models.
Date: February 1, 1999
Creator: de Jager, Kees
Partner: UNT Libraries Government Documents Department

What invariant one-particle multiplicity distributions and two-particle correlations are telling us about relativistic heavy-ion collisions

Description: The authors have used a nine-parameter expanding source model that includes special relativity, quantum statistics, resonance decays, and freeze-out on a realistic hypersurface in spacetime to analyze in detail invariant {pi}{sup +}, K{sup +}, and K{sup {minus}} one-particle multiplicity distributions and {pi}{sup +} and {pi}{sup {minus}} two-particle correlations in nearly central collisions of Pb + Pb at p{sub lab}/A = 158 GeV/c. These studies confirm an earlier conclusion for nearly central collisions of Si + Au at p{sub lab}/A = 14.6 GeV/c that the freeze-out temperature is less than 100 meV and that both the longitudinal and transverse collective velocities -- which are anti-correlated with the temperature -- are substantial. The authors also reconciled their current results with those of previous analyses that yielded a much higher freeze-out temperature of approximately 140 meV for both Pb + Pb collisions at p{sub lab}/A = 158 GeV/c and other reactions. One type of analysis was based upon the use of a heuristic equation that neglects relativity to extrapolate slope parameters to zero particle mass. Another type of analysis utilized a thermal model in which there was an accumulation of effects from several approximations. The future should witness the arrival of much new data on invariant one-particle multiplicity distributions and two-particle correlations as functions of bombarding energy and/or size of the colliding nuclei. The proper analysis of these data in terms of a realistic model could yield accurate values for the density, temperature, collective velocity, size, and other properties of the expanding matter as it freezes out into a collection of noninteracting hadrons. A sharp discontinuity in the value of one or more of these properties could conceivably be the long-awaited signal for the formation of a quark-gluon plasma or other new physics.
Date: February 1, 1998
Creator: Nix, J.R.; Strottman, D.; Hecke, H.W. van; Schlei, B.R.; Sullivan, J.P. & Murray, M.J.
Partner: UNT Libraries Government Documents Department

The 1992 FRDM mass model and unstable nuclei

Description: We discuss the reliability of a recent global nuclear-structure calculation in regions far from {beta} stability. We focus on the results for nuclear masses, but also mention other results obtained in the nuclear-structure calculation, for example ground-state spins. We discuss what should be some minimal requirements of a nuclear mass model and study how the macroscopic-microscopic method and other nuclear mass models fullfil such basic requirements. We study in particular the reliability of nuclear mass models in regions of nuclei that were not considered in the determination of the model parameters.
Date: February 1, 1994
Creator: Moeller, P. & Nix, R. J.
Partner: UNT Libraries Government Documents Department

Mass model for unstable nuclei

Description: We present some essential features of a macroscopic-microscopic nuclear-structure model, with special emphasis on the results of a recent global calculation of nuclear masses. We discuss what should be some minimal requirements of a nuclear mass model and study how the macroscopic-microscopic method and other nuclear mass models fulfil such basic requirements. We study in particular the reliability of nuclear mass models in regions of nuclei that were not considered in the determination of the model parameters.
Date: February 1, 1994
Creator: Moeller, P. & Nix, J. R.
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

Shell model calculations for exotic nuclei

Description: In this paper we review the progress of the shell-model approach to understanding the properties of light exotic nuclei (A < 40). By shell-model'' we mean the consistent and large-scale application of the classic methods discussed, for example, in the book of de-Shalit and Talmi. Modern calculations incorporate as many of the important configurations as possible and make use of realistic effective interactions for the valence nucleons. Properties such as the nuclear densities depend on the mean-field potential, which is usually separately from the valence interaction. We will discuss results for radii which are based on a standard Hartree-Fock approach with Skyrme-type interactions.
Date: February 1, 1990
Creator: Brown, B.A. (Michigan State Univ., East Lansing, MI (USA)); Warburton, E.K. (Brookhaven National Lab., Upton, NY (USA)) & Wildenthal, B.H. (New Mexico Univ., Albuquerque, NM (USA). Dept. of Physics and Astronomy)
Partner: UNT Libraries Government Documents Department

Report to the DOE Nuclear Data Committee 1987

Description: Both measurements and calculations in the field of nuclear data applications are reported. New measurements include the discovery of two new Lr isotopes, the energy-level structure of Mo-93, a probe of the shell crossing at A = 40 via beta decay (experiment and theory), proton and neutron transition densities in Li-6 and Li-7 from a comparative study of proton and neutron scattering at 24 MeV, measurement of the neutron induced fission cross section of Cm-242, quadrupole moments and spectroscopy of Po-210 with Bi-209(t,2n) reaction, excitation functions for Y-89 + p over the range 5 to 40 MeV, excitation functions for Y-89 + d over the range 3 to 40 MeV, and the nuclear structure of Th-231. New calculations reported include the gamma ray cascades in the code ALICE, low energy neutron capture of neutron rich target nuclides, exploratory (n,f) cross section calculations for the U-235 1/2+ isomer, calculated photon induced isomer production in Lu-176 and its impact on the use of Lu-176 as a stellar chronometer and/or thermometer, disagreement between measured capture gamma ray spectra and calculations, electromagnetic moments for Sr-88 and Sr-86, shell model calculations of first forbidden beta decay in the mass 40 region, and dipole strength function studies in the actinide mass region. 8 refs., 7 figs., 2 tabs. (DWL)
Date: February 1, 1987
Creator: Lanier, R.G. & White, R.G.
Partner: UNT Libraries Government Documents Department

PRECO-D2: program for calculating preequilibrium and direct reaction double differential cross sections

Description: The code PRECO-D2 uses the exciton model for preequilibrium nuclear reactions to describe the emission of particles with mass numbers of 1 to 4 from an equilibrating composite nucleus. A distinction is made between open and closed configurations in this system and between the multi-step direct (MSD) and multi-step compound (MSC) components of the preequilibrium cross section. Additional MSD components are calculated semi-empirically to account for direct nucleon transfer reactions and direct knockout processes involving cluster degrees of freedom. Evaporation from the equilibrated composite nucleus is included in the full MSC cross section. Output of energy differential and double differential cross sections is provided for the first particle emitted from the composite system. Multiple particle emission is not considered. This report describes the reaction models used in writing PRECO-D2 and explains the organization and utilization of the code. 21 refs.
Date: February 1, 1985
Creator: Kalbach, C.
Partner: UNT Libraries Government Documents Department

Inelastic strong interactions at high energies. Annual progress report, June 1, 1979-May 1, 1980. [Univ. of Cincinnati, 6/1/79-5/1/80]

Description: Investigations in the area of Grand Unified Field Theories were begun. Various ways of breaking the SU(5) symmetric theory of Georgi and Glashow were studied. As usual, an approx. 24 of Higgs breaks the symmetry from SU(5) to SU(3)/sub c/xSU(2)xU(1). It was found that an approx. 45 of Higgs is acceptable for breaking the symmetry from SU(3)/sub c/xSU(2)xU(1) to SU(3)/sub c/xU(1)/sub em/. In addition phenomenologically correct quark-lepton mass ratios are obtained by use of renormalization-group techniques if there are 6 generations of particles in the theory. Efforts directed at the development of approximate methods for extracting information from quantum field theories were continued. The quantum mechanics of polynomial potentials as a model for quantum field theories was investigated. A perturbation expansion for the energy levels and wave functions was constructed and has been proven to be convergent for arbitrary values of the coupling constants, in contrast to ordinary perturbation expansions that have a zero radius of convergence. The physical significance of the new perturbation expansions was explored both in the weak and strong coupling limits.
Date: February 1, 1980
Creator: Suranyi, P.
Partner: UNT Libraries Government Documents Department

Thermodynamic interpretation of multiparticle emission in relativistic heavy ion collisions

Description: The scattering of the heavy ion Ne from NaF is analyzed at relativistic energy. The spectra of the emission fragments are studied for evidence of a thermodynamic-hydrodynamic collective motion. The spectra of pion, deuteron, and proton emission are fitted for fixed beam and target. The fit is consistent with an interpretation of an expanding hot fluid of interacting nucleons. 2 figures.
Date: February 1, 1980
Creator: Gleeson, A.M. & Raha, S.
Partner: UNT Libraries Government Documents Department

Coupled channel alpha decay theory for even- and odd-mass light and heavy nuclei

Description: Four major approaches to the theoretical calculation of alpha decay widths were examined for light and heavy, even- and odd-mass nuclei. Application of the microscopic shell model rate theory as well as macroscopic models utilizing the coupled-channel formalism were studied. Use of the R-matrix and S-matrix theories have been applied in order to overcome problems involving dependency on the connection radius and nuclear potential parameters of the relative and absolute alpha decay widths. 105 references. (JFP)
Date: February 1, 1978
Creator: Rauscher, E.A.
Partner: UNT Libraries Government Documents Department

Nuclear data development and shield design for neutrons below 60 MeV

Description: A nuclear data library was created for medium-energy-neutron-transport calculations. The 60-group library includes P/sub 5/ cross sections in standard LASL format for H, B, C, N, O, Si, Fe, and W. The 60-group structure was chosen from a sensitivity analysis of a thick iron shield calculated with a 50-MeV deuteron-on-beryllium neutron source spectrum and a 121-group cross-section set. The library combines processed ENDF/B-IV cross-section data below 20 MeV and higher-energy cross-section parameters calculated with the intranuclear-cascade and evaporation model. A 6-group version of the library is used in the design of a shield-collimator unit for fast-neutron radiotherapy. While the shield is specific for the 50-MeV d/sup +/--Be neutron source presently used in cancer therapy at Texas A and M University, the cross sections and methods developed are applicable to the problems of medium-energy-neutron shielding in general. 28 figures, 21 tables, 132 references.
Date: February 1, 1978
Creator: Wilson, W.B.
Partner: UNT Libraries Government Documents Department

Scattering of 14-Mev Neutrons From Nitrogen and Oxygen

Description: The differential cross sections for elastic scattering of 14-Mev neutrons from nitrogen and oxygen were measured in the angular range from 17 to 140 deg , using liquid targets and annular ring geometry. Inelastic scattering to the 2.31 and 3.95-Mev levels in N/sup 14/ and to the levels near 6 and 7 Mev in O/sup 16/ was investigated over a more restricted angular range. The 2.31-Mev level in N/sup 14/ was not excited appreciably, in disagreement with previously reported results. For both elements, the elastic scattering cross sections (determined to an accuracy of 10%) were found to be appreciably higher than the optical model predictions by Rjorklund and Fernbach for scatterirg angles larger than 70 deg . The inelastic cross sections measured are, within experimental accuracy, the same as the corresponding (p,p') cross sections. (auth)
Date: February 27, 1963
Creator: Bauer, R. W.; Anderson, J. D. & Christensen, L. J.
Partner: UNT Libraries Government Documents Department

On Closed Shells in Nuclei

Description: It has been suggested in the past that special numbers of neutrons or protons in the nucleus form a particularly stable configuration.{sup1} The complete evidence for this has never been summarized, nor is it generally recognized how convincing this evidence is. That 20 neutrons or protons (Ca{sup40}) form a closed shell is predicted by the Hartree model. A number of calculations support this fact.{sup2} These considerations will not be repeated here. In this paper, the experimental facts indicating a particular stability of shells of 50 and 82 protons and of 50, 82, and 126 neutrons will be listed.
Date: February 1, 1948
Creator: Mayer, M.G.
Partner: UNT Libraries Government Documents Department