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Universal correlations of nuclear observables and the structure of exotic nuclei

Description: Despite the apparent complexity of nuclear structural evolution, recent work has shown a remarkable underlying simplicity that is unexpected, global, and which leads to new signatures for structure based on the easiest-to-obtain data. As such they will be extremely valuable for use in the experiments with low intensity radioactive beams. Beautiful correlations based either on extrinsic variables such as N{sub p}N{sub n} or the P-factor or correlations between collective observables themselves have been discovered. Examples to be discussed include a tri-partite classification of structural evolution, leading to a new paradigm that discloses certain specific classes of nuclei, universal trajectories for B(E2: w{sub 1}{sup +} {r_arrow} 0{sub 1}{sup +}) values and their use in extracting hexadecapole deformations from this observable alone, the use of these B(E2) values to identify shell gaps and magic numbers in exotic nuclei, the relationship of {beta} and {gamma} deformations, and single nucleon separation energies. Predictions for nuclei far off stability by interpolation will also be discussed.
Date: Autumn 1996
Creator: Casten, R. F. & Zamfir, N. V.
Partner: UNT Libraries Government Documents Department

Superdeformation in the mass A {approximately} 80 region

Description: A new island of superdeformed nuclei with major-to-minor axis ratio of 2:1 has recently been discovered in the A {approximately} 80 medium-mass region, confirming the predictions for the existence of a large SD gap at particle number N,Z {approximately} 44. The general properties of more than 20 bands observed so far will be reviewed here, and compared with those of the superdeformed bands in the heavier nuclei.
Date: December 31, 1996
Creator: Baktash, C.
Partner: UNT Libraries Government Documents Department

In-beam gamma-ray spectrometric measurements of multi-body breakup reactions for E{sub n} between threshold and 40 MeV

Description: A system for in-beam gamma-ray spectrometric measurements to study inelastic neutron scattering has been extended to increasing incident neutron energies to study multi-body breakup reactions on light and medium-weight elements. The (n,2n{gamma}) cross sections are generally the largest; however, reactions of the types (n,{alpha}{gamma}), (n,np{gamma}) and (n,3n{gamma}) have been observed. In addition to improved understanding of reaction channels studied by other techniques, this method provides data for some reactions, e.g. {sup 56}Fe(n,3n){sup 54}Fe, which have not been observed previously.
Date: April 1995
Creator: Dickens, J. K. & Larson, D. C.
Partner: UNT Libraries Government Documents Department

Self-consistent methods in nuclear structure physics

Description: The authors present a very brief description of the Hartree Fock method in nuclear structure physics, discuss the numerical methods used to solve the self-consistent equations, and analyze the precision and convergence properties of solutions. As an application, they present results pertaining to quadrupole moments and single-particle quadrupole polarizations in superdeformed nuclei with A {approximately} 60.
Date: November 1, 1997
Creator: Dobaczewski, J.
Partner: UNT Libraries Government Documents Department

Electric monopole transitions: What they can tell us about nuclear structure

Description: A brief survey of E0 strength in a number of nuclei in different regions of the nuclear chart is presented. The connection between E0 strength and shape coexistence is reviewed. Nuclear structure information obtained from measurements of electric monopole transitions in {sup 184}Pt and {sup 187}Au is discussed. Plans for future experiments utilizing radioactive ion beams and E0 internal-pair-formation is presented.
Date: December 31, 1995
Creator: Zganjar, E.F. & Wood, J.L.
Partner: UNT Libraries Government Documents Department

Masses new and old: Measurements of 39 isotopes from {sup 51}Ca to {sup 72}Ni

Description: The most recent mass measurements using the Time-of-Flight Isochronous (TOFI) spectrometer are presented. The masses of 8 neutron-rich nuclei are reported for the first time. Good agreement between these results and a previous TOFI experiment is observed except for the most neutron-rich isotopes of vanadium through iron where the present results are more bound and in better agreement with theory. An unreasonably low two-neutron separation energy for {sup 68}Ni suggests the presence of a high-lying, long-lived isomeric state in this nucleus. These results are contrasted with the latest shell model calculations and a variety of mass model predictions. In general good agreement is found, however, an enhanced binding-energy region centered around {sup 51}Ca and {sup 52-54}Sc persists. The neutron-excess dependence of neutron and proton pairing energies in the f{sub 7/2} shell are found to be considerably weaker than those obtained in a global fit.
Date: December 1995
Creator: Vieira, D. J.; Seifert, H. L. & Wouters, J. M.
Partner: UNT Libraries Government Documents Department

The role of statistics and thermodynamics in nuclear multifragmentation

Description: The natural limit of binomial reducibility in nuclear multifragmentation is observed in excitation functions for intermediate mass fragments (IMF) of a given element Z. The multiplicity distributions for each window of transverse energy are Poissonian. Thermal scaling is observed in the linear Arrhenius plots constructed from the average multiplicity of each element. Emission barriers are extracted from the slopes of the Arrhenius plots and their possible origin is discussed.
Date: March 1, 1998
Creator: Moretto, L. G.; Beaulieu, L.; Phair, L. & Wozniak, G. J.
Partner: UNT Libraries Government Documents Department

Study of nuclear fragment emission in proton heavy nucleus collision from 10 to 500 GeV/c

Description: We propose to measure the double differential cross section of nuclear fragments (2 less than or equal to Z less than or equal to 16), for a given incident momentum, produced by proton heavy nucleus (20 less than or equal to Z less than or equal to 80) collisions in the 10 to 500 GeV/c momentum range. Recent experimental results and theoretical speculations suggest collective nuclear motion is initiated by the passage of a fast proton through a heavy nucleus. The novel feature of this experiment is the determination of the energy dependence of the excitation mechanism. Because nuclear fragments are best studied from thin targets, one needs a very high beam flux to obtain sufficient event rates. These considerations make the Internal Target Area with a heavy gas jet target the ideal place to initiate our experimental program. The detection system will consist of four conventional $delta$E- E semiconductor telescopes. (auth)
Date: September 16, 1975
Partner: UNT Libraries Government Documents Department

The P-factor and atomic mass systematics: Application to medium mass nuclei

Description: The P formalism was applied to atomic mass systematics for medium and heavy nuclei. The P-factor linearizes the structure-dependent part of the nuclear mass in those regions which are free from subshell effects indicating that the attractive quadrupole p-n force plays an important role in determining the binding of valence nucleons. Where marked non-linearities occur, the P-factor provides a means for recognizing subshell closures and/or other structural features not embodied in the simple assumptions of abrupt shell or subshell changes. These are thought to be regions where the monopole part of the p-n interaction is highly orbit dependent and alters the underlying single-particle structure as a function of A, N or Z. Finally, in those regions where the systematics are smooth and subshells are absent, the P-factor provides a means for predicting masses of some nuclei far-from-stability by interpolation rather than by extrapolation. 5 figs.
Date: January 1, 1988
Creator: Brenner, D.S.; Haustein, P.E. & Casten, R.F.
Partner: UNT Libraries Government Documents Department

Preliminary considerations of an intense slow positron facility based on a sup 78 Kr loop in the high flux isotopes reactor

Description: Suggestions have been made to the National Steering Committee for the Advanced Neutron Source (ANS) by Mills that provisions be made to install a high intensity slow positron facility, based on a {sup 78}Kr loop, that would be available to the general community of scientists interested in this field. The flux of thermal neutrons calculated for the ANS is E + 15 sec{sup {minus}1} m{sup {minus}2}, which Mills has estimated will produce 5 mm beam of slow positrons having a current of about 1 E + 12 sec {sup {minus}1}. The intensity of such a beam will be a least 3 orders of magnitude greater than those presently available. The construction of the ANS is not anticipated to be complete until the year 2000. In order to properly plan the design of the ANS, strong considerations are being given to a proof-of-principle experiment, using the presently available High Flux Isotopes Reactor, to test the {sup 78}Kr loop technique. The positron current from the HFIR facility is expected to be about 1 E + 10 sec{sup {minus}1}, which is 2 orders of magnitude greater than any other available. If the experiment succeeds, a very valuable facility will be established, and important formation will be generated on how the ANS should be designed. 3 refs., 1 fig.
Date: January 1, 1990
Creator: Hulett, L.D. Jr.; Donohue, D.L.; Peretz, F.J.; Montgomery, B.H. & Hayter, J.B.
Partner: UNT Libraries Government Documents Department

Workshop on nuclear structure at moderate and high spin: Slide report

Description: The workshop was scheduled to coincide with the beginning of operation of a number of large arrays of Compton-suppressed germanium detectors. The workshop was divided into 14 sessions containing 3 presentations each. The topics of these sessions were superdeformation, heavy rare earths, single-particle configurations, band termination, continuum properties, light rare-earths, new techniques, high temperatures, transfer reactions, transition region, shapes, lifetimes, and moments. This publication consists of the slides used in all of the presentations at the workshop.
Date: October 1, 1986
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

ENDF-201: ENDF/B-VI summary documentation

Description: Responsibility for oversight of the ENDF/B Evaluated Nuclear Data file lies with the Cross Section Evaluation Working Group (CSEWG), which is comprised of representatives from various governmental and industrial laboratories in the United States. Individual evaluations are provided by scientists at several US laboratories, including significant contributions by scientists from all over the world. In addition, ENDF/B-VI includes for the first time complete evaluations for three materials that were provided from laboratories outside the US. All data are checked and reviewed by CSEWG, and the data file is maintained and issued by the National Nuclear Data Center at Brookhaven National Laboratory. The previous version of the library, ENDF/B-V, was issued in 1979, and two revisions to the data file were provided in subsequent years, the latest occurring in 1981. A total of 75 new or extensively modified neutron sublibrary evaluations are included in ENDF/B-VI, and are summarized in this document. One incident proton sublibrary is described for Fe{sup 56}. The remaining evaluations in ENDF/B-VI have been carried over from earlier versions of ENDF, and have been updated to reflect the new formats. The release of ENDF/B-VI was carried out between January and June of 1990, with groups of materials being released on tapes.'' Table 1 is an index to the evaluation summaries, and includes the material identification or MAT number, the responsible laboratory, and the tape'' number. These evaluations have been released without restrictions on their distribution or use.
Date: October 1, 1991
Creator: Rose, P.F. (comp.)
Partner: UNT Libraries Government Documents Department

Some perspectives on high-spin physics. [Concluding talk]

Description: This report consists of a talk presented at the conclusion of a meeting. As is typical, this talk does not truly summarize what was said at the meeting; the author acknowledges that he discusses several areas of interest to him - some of which were covered at the meeting and some of which were not. High-spin phenomena are divided into collective and noncollective regions, each of which exhibits resolved and unresolved ..gamma.. rays. Rotational spectra in the unresolved collective region are discussed; correlations between ..gamma..-ray energy and spin and between ..gamma..-ray energies in a rotational nucleus are pointed out. In the resolved noncollective region, the spectrum of /sup 152/Dy exhibits a straight line when energy is plotted vs I(I+1); it is concluded that shell effects explain this behavior. In summary, the author in his talk has tried to indicate areas of current research interest. 10 figures. (RWR)
Date: August 1, 1979
Creator: Stephens, F.S.
Partner: UNT Libraries Government Documents Department

Nuclear states and shapes at high spin. [Good review]

Description: As angular momentum is added to a nucleus, the balance of forces acting upon it to determine its shape, moment of inertia, mode of rotation, and type of level structure may undergo a series of changes. At relatively low spins a deformed nucleus will rotate collectively, and one may see the effect of Coriolis antipairing in gradually increasing the moment of inertia. Around spin 12 to 16 h-bar there may be an abrupt change (backbending) when a pair of high-j nucleons unpairs and the nucleons align with the axis of rotation; this process allows the nucleus to slow its collective rotation. This process, the start of a sharing of angular momentum between single-particle motion and the collective rotation, gives a lower total energy and corresponds to a change toward triaxiality in the shape of the nucleus. At much higher spins discrete ..gamma..-ray transitions can no longer be observed. This is the regime of continuum spectra; all the information on these high-spin states (to 65 h-bar) is contained in these continuum cascades. Knowledge is accumulating on how to study these spectra, experimentally and theoretically, and new techniques offer promise of revealing a great deal of information about the shapes and properties of very high spin states. 71 references, 34 figures.
Date: August 1, 1980
Creator: Diamond, R.M.
Partner: UNT Libraries Government Documents Department

Theory of Moessbauer line broadening due to diffusion

Description: We have calculated the line broadening of the Moessbauer line due to diffusion of Moessbauer atoms via single vacanices. We take into account the perturbation of vacancy jumps in the neighbourhood of an impurity Moessbauer atom (e.g. Fe in Al) using the 5-frequency model. The anisotropy of the line width is given by the Fourier transform of the final distribution of a Moessbauer atom after an encounter with a vacancy. This distribution is calculated by Monte Carlo computer simulation. 3 figures, 1 tables.
Date: December 1, 1981
Creator: Schroeder, K.; Wolf, D. & Dederichs, P.H.
Partner: UNT Libraries Government Documents Department