Nuclear structure studies of medium-mass nuclei using large Ge arrays

The advent of large Ge arrays and their ancillary detectors has greatly advanced spectroscopic studies of the medium-mass nuclei. These nuclei undergo rapid shape changes as a function of spin, excitation energy and particle number and, thus, provide a unique laboratory to test and refine a variety of theoretical models. Following a brief review of the physics motivation, some of the highlights of the experimental results obtained with the help of these powerful detector systems will be discussed. Among results presented here are the newly-discovered island of superdeformation in the A{approximately}80 mass region, and the high-spin band structures in the N{approximately}Z nuclei. These band structures may be understood in the framework of the conventional cranking models, without the introduction of additional T=0 neutron-proton pairing correlations

Diffusion of Lithium Ions in Lithium-Argyrodite Solid-State Electrolytes from Equilibrium and Nonequilibrium Molecular Dynamics Simulations

The use of solid-state electrolytes to provide safer, next-generation rechargeable batteries is becoming more feasible as new materials with greater stability and higher ionic diffusion coefficients are designed. However, accurate determination of diffusion coefficients in solids is problematic and reliable calculations are highly sought-after. In this paper we compare diffusion coefficients calculated using nonequilibrium and equilibrium ab initio molecular dynamics simulations for highly diffusive solid-state electrolytes for the first time, to demonstrate the accuracy that can be obtained. Moreover, we show that ab initio nonequilibrium molecular dynamics can be used to determine diffusion coefficients when the diffusion is too slow for it to be feasible to obtain them using ab initio equilibrium simulations. Thereby, using ab initio nonequilibrium molecular dynamics simulations we are able to obtain accurate estimates of the diffusion coefficients of Li ions in Li$_6$PS$_5$Cl and Li$_5$PS$_4$Cl$_2$, two promising electrolytes for all-solid-state batteries. Furthermore, these calculations show that the diffusion coefficient of lithium ions in Li$_5$PS$_4$Cl$_2$ is higher than many other potential all-solid-state electrolytes, making it promising for future technologies. The reasons for variation in conductivities determined using computational and experimental methods are also discussed. It is demonstrated that small degrees of disorder and vacancies can result in orders of magnitude differences in diffusivities of Li ions in Li$_6$PS$_5$Cl, and these factors are likely to contribute to inconsistencies observed in experimentally reported values. Notably, the introduction of Li-vacancies and disorder can enhance the ionic conductivity of Li$_6$PS$_5$Cl.Comment: 32 pages, 8 figures, 2 table

Prompt Alpha Decay of a Well-deformed Band in 58Ni

Two excited well-deformed bands have been observed in the semi-magic nucleus Ni-58. One of the bands was observed to partially decay by emission of a prompt discrete alpha particle that feeds the 2949 keV 6(+) spherical yrast state in the daughter nucleus Fe-54. This constitutes the first observation of prompt alpha emission from states lying in the deformed secondary minimum of the nuclear potential. gamma -ray linking transitions via several parallel paths establish the spin. parity, and excitation energy of this deformed band in Ni-58

Prompt Alpha Decay of a Well-deformed Band in 58Ni

Two excited well-deformed bands have been observed in the semi-magic nucleus Ni-58. One of the bands was observed to partially decay by emission of a prompt discrete alpha particle that feeds the 2949 keV 6(+) spherical yrast state in the daughter nucleus Fe-54. This constitutes the first observation of prompt alpha emission from states lying in the deformed secondary minimum of the nuclear potential. gamma -ray linking transitions via several parallel paths establish the spin. parity, and excitation energy of this deformed band in Ni-58

Tests and applications of self-consistent cranking in the interacting boson model

The self-consistent cranking method is tested by comparing the cranking calculations in the interacting boson model with the exact results obtained from the SU(3) and O(6) dynamical symmetries and from numerical diagonalization. The method is used to study the spin dependence of shape variables in the $sd$ and $sdg$ boson models. When realistic sets of parameters are used, both models lead to similar results: axial shape is retained with increasing cranking frequency while fluctuations in the shape variable $\gamma$ are slightly reduced.Comment: 9 pages, 3 ps figures, Revte

Magnetic moments of 2 1 + states in 124,126,128 Sn

The g factors of the first-excited states of stable 124Sn and radioactive 126,128Sn were measured by the recoil-in-vacuum method with comparatively high precision. The experiments were performed at the Holifield Radioactive Ion Beam Facility by Coulomb e

Time-odd components in the mean field of rotating superdeformed nuclei

Rotation-induced time-odd components in the nuclear mean field are analyzed using the Hartree-Fock cranking approach with effective interactions SIII, SkM*, and SkP. Identical dynamical moments ${{\cal J}^{(2)}}$ are obtained for pairs of superdeformed bands $^{151}$Tb(2)--$^{152}$Dy(1) and $^{150}$Gd(2)--$^{151}$Tb(1). The corresponding relative alignments strongly depend on which time-odd mean-field terms are taken into account in the Hartree-Fock equations.Comment: 23 pages, ReVTeX, 6 uuencoded postscript figures include

First-excited state g factor of Te 136 by the recoil in vacuum method

The g factor of the first 2+ state of radioactive 136Te with two valence protons and two valence neutrons beyond double-magic 132Sn has been measured by the recoil in vacuum (RIV) method. The lifetime of this state is an order of magnitude longer than the lifetimes of excited states recently measured by the RIV method in Sn and Te isotopes, requiring a new evaluation of the free-ion hyperfine interactions and methodology used to determine the g factor. The calibration data are reported and the analysis procedures are described in detail. The resultant g factor has a similar magnitude to the g factors of other nuclei with an equal number of valence protons and neutrons in the major shell. However, an unexpected trend is found in the g factors of the N=84 isotones, which decrease from 136Te to 144Nd. Shell model calculations with interactions derived from the CD Bonn potential show good agreement with the g factors and E2 transition rates of 2+ states around 132Sn, confirming earlier indications that 132Sn is a good doubly magic core

Study of spin-temperature effects using energy-ordered continuum gamma-ray spectroscopy technique

We have investigated a new continuum {gamma}-ray spectroscopy technique which is based on the detection of all emitted {gamma} rays in a 4{pi} detector system, and ordering them according to their energies on an event-by-event basis. The technique allows determination of gamma strength functions, and rotational damping width as a function of spin and temperature. Thus, it opens up the possibility of studying the onset of motional narrowing, order-to-chaos transition, and the mapping of the evolution of nuclear collectivity with a spin and temperature. Application of the technique for preferential entry-state population, exit-channel selection, and feeding of the discrete states via selective pathways will be discussed. 20 refs., 4 figs