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Observation of the single step links of the yrast superdeformed band in {sup 194}Pb

Description: The EUROGAM array has been used to investigate the decay out of the yrast superdeformed (SD) band in {sup 194}Pb. Eigth single step decays from the lowest observed SD states to low-lying states at normal deformation (ND) have been identified. From this observation, the excitation energy (4877 {plus_minus} 1.5 keV) and the spin (6+) of the lowest observed SD state in {sup 194}Pb are established.
Date: December 1, 1996
Creator: Hannachi, F.; Lopez-Martens, A. & Schueck, C.
Partner: UNT Libraries Government Documents Department

DOE 1994 review of nuclear physics

Description: Understanding the physics of nuclei at the limits of deformation. Superdeformed nuclei (i.e., nuclei with a major-to-minor axis ratio of {approximately}2:1) provide a unique laboratory for nuclear structure studies at the limits of observable deformation. Islands of superdeformation are predicted and found throughout the table of isotopes. We have focused our attention on the A = 190 region, since neutron deficient Hg and Pb nuclei were predicted to support a stable superdeformed minimum at zero angular momentum. We are making major contributions to the development of this region of superdeformation. We find general agreement with fully 3-D Hartree Fock calculations done with a microscopic interaction, including pairing. Our measurements test predictions in the second well which are based on extrapolation of nuclear theory determined at `normal` deformation. In addition, unusual phenomena are expected because of the large difference in shape between well I and well II states. Our experiments require the sensitivity and resolution of large scale Ge detector arrays.
Date: February 8, 1994
Creator: Becker, J.
Partner: UNT Libraries Government Documents Department

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

Signature Inversion in Odd-odd Nuclei

Description: Trends in the energy staggering of the {pi}h{sub 11/2}{nu}i{sub 13/2} and {pi}h{sub 11/2} {nu}h{sub 11/2} bands in the mass 160 and 130 regions, respectively, have been investigated in order to better understand the origin of signature inversion. While the A {approx} 160 nuclei behave in a consistent manner, a more complicated scenario is observed in the mass 130 region. As a result of our experiments on the lightest Pr nuclei, the systematics of these Z = 59 nuclei have been extended, which aids in the understanding of the latter region. Triaxial deformation, a pn interaction, and quadrupole pairing are considered as possible contributors to this effect. As all the chiral-twin bands that are known have signature inversion in the favored band, a possible link between the two phenomena should be considered.
Date: September 10, 2001
Creator: Riedinger, L.L.
Partner: UNT Libraries Government Documents Department

The Nuclear Collective Motion

Description: Current developments in nuclear structure are discussed from a theoretical perspective. First, the progress in theoretical modeling of nuclei is reviewed. This is followed by the discussion of nuclear time scales, nuclear collective modes, and nuclear deformations. Some perspectives on nuclear structure research far from stability are given. Finally, interdisciplinary aspects of the nuclear many-body problem are outlined.
Date: March 20, 2001
Creator: Nazarewicz, W.
Partner: UNT Libraries Government Documents Department

Macroscopic-microscopic mass models

Description: We discuss recent developments in macroscopic-microscopic mass models, including the 1992 finite-range droplet model, the 1992 extended- Thomas-Fermi Strutinsky-integral model, and the 1994 Thomas-Fermi model, with particular emphasis on how well they extrapolate to new regions of nuclei. We also address what recent developments in macroscopic-microscopic mass models are teaching us about such physically relevant issues as the nuclear curvature energy, a new congruence energy arising from a greater-than-average overlap of neutron and proton wave functions, the nuclear incompressibility coefficient, and the coulomb redistribution energy arising from a central density depression. We conclude with a brief discussion of the recently discovered rock of metastable superheavy nuclei near {sup 272}110 that had been correctly predicted by macroscopic-microscopic models, along with a possible new tack for reaching an island near {sup 290}110 beyond our present horizon.
Date: July 1995
Creator: Nix, J. R. & Moller, P.
Partner: UNT Libraries Government Documents Department

Superdeformation and hyperdeformation at high spin

Description: A short review of theoretical and experimental studies of superdeformation and hyperdeformation is presented. Recent results, based on calculations carried out in a four dimensional deformation space, are presented. Very extended nuclear shapes ranging in mass from A=150 to A=200 are discussed.
Date: August 1, 1995
Creator: Chasman, R.R.
Partner: UNT Libraries Government Documents Department

Superdeformed shapes and configurations in thallium nuclei

Description: Superdeformation studies in {sup 189,191,192}Tl at Gammasphere are discussed. New results on {sup 191}Tl are the observation of interband transitions between the signature partner E2 bands and the measurement of an average quadrupole moment (Q{sub 0} = 18 {+-} 1 eb) for these superdeformed structures. These data enable them to derive absolute M1 strengths and confirm that the 81st proton occupies the [642]5/2 orbital. Tentative data for one superdeformed sequence in {sup 189}Tl are consistent with the prediction of a decrease in quadrupole deformation for the lightest nuclei at the limit of this island of superdeformation.
Date: September 1997
Creator: Reviol, W.; Mueller, W. F. & Riedinger, L. L.
Partner: UNT Libraries Government Documents Department

Progress Report on Nuclear Spectroscopic Studies

Description: The experimental program in nuclear physics at the University of Tennessee, Knoxville, is led by Professors Carrol Bingham, Lee Riedinger, and Soren Sorenseni who respectively lead the studies of the exotic decay modes of nuclei far from stability, the program of high-spin research, and our effort in relativistic heavy-ion physics. Over the years, this broad program of research has been successful partially because of the shared University resources applied to this group effort. The proximity of the Oak Ridge National Laboratory has allowed us to build extremely strong programs of joint research, and in addition to play an important leadership role in the Joint Institute for Heavy Ion Research (JIHIR). Our experimental program is also very closely linked with those at other national laboratories: Argonne (collaborations involving the Fragment Mass Analyzer (FMA) and {gamma}-ray arrays), Brookhaven (the RHIC and Phenix projects), and Berkeley (GAMMASPHERE). We have worked closely with a variety of university groups in the last three years, especially those in the UNISOR and now UNIRIB collaborations. And, in all aspects of our program, we have maintained close collaborations with theorists, both to inspire the most exciting experiments to perform and to extract the pertinent physics from the results. The specific areas discussed in this report are: properties of high-spin states; study of low-energy levels of nuclei far from stability; and high energy heavy-ion physics.
Date: January 16, 1996
Creator: Bingham, C. R.; Riedinger, L. L. & Sorensen, S. P.
Partner: UNT Libraries Government Documents Department

Universal correlations of nuclear observables and new signatures of structure in exotic nuclei: A review

Description: Recently, several nearly universal correlations of nuclear observables, spanning nuclei from singly magic to rotor, have been discovered. The simple global behavior revealed by these correlations discloses new signatures of structure that require a knowledge only of the energies of the first two excited states in even-even nuclei and the B(E2 : 2{sub 1}{sup +} {yields} 0{sub 1}{sup +}) value. Since these are the simplest to-obtain data in new nuclei in unexplored regions, they should be especially valuable in radioactive beam studies of nuclei far from stability where the data will necessarily be sparse compared to that with which is accustomed. This report reviews some of these recent developments.
Date: November 1, 1995
Creator: Casten, R.F. & Zamfir, N.V.
Partner: UNT Libraries Government Documents Department

Test of {Delta}I = 2 staggering in the superdeformed bands of {sup 194}Hg

Description: The presence of {Delta}I = 2 staggering in the three known superdeformed bands of {sup 194}Hg has been reexamined in a new experiment with Gammasphere. A relative accuracy of better than 30 eV was achieved for most transition energies. No statistically significant oscillations in the transition energies were found for band 1 while staggering patterns were observed in bands 2 and 3. The statistical significance of the observed effects was analyzed. The patterns display some similarities with expectations based on a band crossing picture, even though such a picture cannot reproduce the observations in a straightforward way. No evidence was found for additional superdeformed bands in {sup 194}Hg which could account for possible band-crossings.
Date: June 5, 1996
Creator: Kruecken, R.; Deleplanque, M.A.; Lee, I.Y. & Asztalos, S.
Partner: UNT Libraries Government Documents Department

How close are hyperdeformed states to the scission point?

Description: The HFB method with the Gogny force is used to study the effects of reflection asymmetry at I = 0{h_bar} on the barriers separating superdeformed and hyperdeformed minima from fission in the {sup 176}W and {sup 168}Yb nuclei. The fission barrier for the HD minimum is reduced by 5 MeV in {sup 176}W when reflection asymmetry is taken into account.
Date: December 1, 1996
Creator: Robledo, L.M.; Egido, J.L. & Chasman, R.R.
Partner: UNT Libraries Government Documents Department

Effects of shape differences in the level densities of three formalisms of calculated cross sections

Description: Effects of shape differences in the level densities of three formalisms on calculated cross sections and particle emission spectra are described. Reactions for incident neutrons up to 20 MeV on {sup 58}Ni are chosen for illustrations. Level-density parameters for one of the formalisms are determined from the available neutron resonance data for one residual nuclide in the binary channels and from fitting the measured (n, n{prime}), (n, p), and (n, {alpha}) cross sections for the other two residual nuclides. Level-density parameters for the other two formalisms are determined such that they yield the same values as the above one at two selected energies. This procedure forces the level densities from the three formalisms used for the binary part of the calculation to be as close as possible. The remaining differences are in their energy dependences (shapes). It is shown that these shape differences alone are enough to cause the calculated cross sections and particle emission spectra to be different by up to 60%.
Date: September 1, 1995
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Theoretical nuclear structure and astrophysics. Progress report for 1993--1995

Description: This research effort is directed toward theoretical support and guidance for the developing fields of radioactive ion beam (RIB) physics, computational and nuclear astrophysics, and the interface between these disciplines. The authors are concerned both with the application of existing technologies and concepts to guide the initial RIB program, and the development of new ideas and new technologies to influence the longer-term future of nuclear structure physics and astrophysics. The authors report substantial progress in both areas. One measure of progress is publications and invited material. The research described here has led to more than 70 papers that are published, accepted, or submitted to refereed journals, and to 46 invited presentations at conferences and workshops.
Date: December 31, 1995
Creator: Guidry, M.W.; Nazarewicz, W. & Strayer, M.R.
Partner: UNT Libraries Government Documents Department

Fine structure in deformed proton emitters.

Description: In a recent experiment to study the proton radioactivity of the highly deformed {sup 131}Eu nucleus, two proton lines were detected. The higher energy one was assigned to the ground-state to ground-state decay, while the lower energy, to the ground-state to the 2{sup +} state decay. This constitutes the first observation of fine structure in proton radioactivity. With these four measured quantities, proton energies, half-life and branching ratio, it is possible to determine the Nilsson configuration of the ground state of the proton emitting nucleus as well as the 2{sup +} energy and nuclear deformation of the daughter nucleus. These results will be presented and discussed.
Date: December 7, 1999
Creator: Sonzogni, A. A.; Davids, C. N.; Woods, P. J.; Seweryniak, D.; Carpenter, M. P.; Ressler, J. J. et al.
Partner: UNT Libraries Government Documents Department

Many-Body Correlations in Nuclei and Quantum Dots

Description: Confined quantum many-body systems of a given particle number exhibit a variety of intrinsic shape characteristics as a function of increasing external field and internal thermal excitation. The shell model is an important tool for the theoretical description of these various structures and transitions in nuclei. Another system in which correlations beyond the mean field may play an important role is semiconductor quantum dots. In this Proceedings, the author compares nuclei and quantum dots and their various deformation properties. The author reports on shell-model calculations in nuclei and some recent mean-field calculations of the thermal properties of quantum dots.
Date: August 31, 2001
Creator: Dean, D. J.
Partner: UNT Libraries Government Documents Department

Phase transitions in nuclear physics

Description: A critical overview of the low energy phase transitions in nuclei is presented with particular attention to the 2nd (1st) order pairing phase transitions, and to the 1st order liquid-vapor phase transition. The role of fluctuations in washing out these transitions is discussed and illustrated with examples. A robust indicator of phase coexistence in multifragmentation is presented.
Date: August 1, 1997
Creator: Moretto, L.G.; Phair, L. & Wozniak, G.J.
Partner: UNT Libraries Government Documents Department

Nuclear structure research. Annual progress report

Description: The most significant development this year has been the realization of a method for estimating EO transition strength in nuclei and the prediction that the de-excitation (draining) of superdeformed bands must take place, at least in some cases, by strong EO transitions. A considerable effort has been devoted to planning the nuclear structure physics that will be pursued using the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge. A significant effort has been devoted to HRIBF target development. This is a critical component of the HRIBF project. Exhaustive literature searches have been made for a variety of target materials with emphasis on thermodynamic properties. Vapor pressure measurements have been carried out. Experimental data sets for radioactive decays in the very neutron-deficient Pr-Eu and Ir-Tl regions have been under analysis. These decay schemes constitute parts of student Ph.D. theses. These studies are aimed at elucidating the onset of deformation in the Pr-Sm region and the characteristics of shape coexistence in the Ir-Bi region. Further experiments on shape coexistence in the neutron-deficient Ir-Bi region are planned using {alpha} decay studies at the FMA at ATLAS. The first experiment is scheduled for later this year.
Date: July 31, 1995
Creator: Wood, J.L.
Partner: UNT Libraries Government Documents Department

Experimental and phenomenological approaches to the structure of exotic nuclei

Description: The structure of exotic nuclei that will become accessible with radioactive beams, especially in extremely neutron-rich nuclei where there is a large ``lever arm`` from the valley of stability, is likely to be quite different from anything we have yet encountered. There have been suggestions of radically-different shell structure due, for example, to more-rounded shell potentials (no ``l{sup 2}`` term in the Nilsson potential) or to weaker l{center_dot}s interactions. Also, the weak binding of the outermost nucleons, the coupling to the continuum, changes in residual p-n and pairing interactions, will all contribute to new types of structure and collectivity. Among other effects, magic numbers are likely to lose their robustness; sequences of shell model orbits might be altered in major ways; the onset, manifestations, and evolution of collectivity could be different; unique parity orbits may revert to their parent shells. Radioactive beams will provide the opportunity to study these exotic nuclei, but, at the same time, the amount of data obtainable win be much less than we are accustomed to. Hence, it will be necessary to develop highly-efficient experimental approaches on the one hand, and new signatures of structure, based on the simplest-to-obtain data, on the other. Recently, progress has been made in both areas, and this work is discussed below.
Date: July 1, 1995
Creator: Casten, R.F. & Zamfir, N.V.
Partner: UNT Libraries Government Documents Department

Gross shell structure of moments of inertia

Description: Average yrast moments of inertia at high spins, where the pairing correlations are expected to be largely absent, were found to deviate from the rigid-body values. This indicates that shell effects contribute to the moment of inertia. We discuss the gross dependence of moments of inertia and shell energies on the neutron number in terms of the semiclassical periodic orbit theory. We show that the ground-state shell energies, nuclear deformations and deviations from rigid-body moments of inertia are all due to the same periodic orbits.
Date: July 1, 2002
Creator: Deleplanque, M.A.; Frauendorf, S.; Pashkevich, V.V.; Chu, S.Y. & Unzhakova, A.
Partner: UNT Libraries Government Documents Department

Correlations in nuclear observables: Towards a synthesis of structural evolution

Description: Global plots of simple nuclear observables reveal new correlations that are compact and universal. These correlations highlight the behavior of ``deviant`` nuclei, disclosing the presence of degrees of freedom not otherwise visible. Correlations of yrast energies show that nearly all nuclei fall into a tripartite classification of seniority, anharmonic vibrator and rotor regimes. These regimes are connected by rapidly evolving zones showing critical phase transitional behavior.
Date: August 1, 1993
Creator: Casten, R. F.; Zamfir, N. V. & Brenner, D. S.
Partner: UNT Libraries Government Documents Department

Nuclear physics: Macroscopic aspects

Description: A systematic macroscopic, leptodermous approach to nuclear statics and dynamics is described, based formally on the assumptions {h_bar} {yields} 0 and b/R << 1, where b is the surface diffuseness and R the nuclear radius. The resulting static model of shell-corrected nuclear binding energies and deformabilities is accurate to better than 1 part in a thousand and yields a firm determination of the principal properties of the nuclear fluid. As regards dynamics, the above approach suggests that nuclear shape evolutions will often be dominated by dissipation, but quantitative comparisons with experimental data are more difficult than in the case of statics. In its simplest liquid drop version the model exhibits interesting formal connections to the classic astronomical problem of rotating gravitating masses.
Date: December 1, 1993
Creator: Swiatecki, W. J.
Partner: UNT Libraries Government Documents Department