High-spin Phenomena Research Articles

Study of high spin phenomena in even-even dysprosium isotopes by using projected shell model

Study of high spin phenomena in even-even dysprosium isotopes by using projected shell model

High-spin phenomena in 194Hg

High-spin states in the isotope 194Hg were populated using the 150Nd(40Ca,4n) reaction at a beam energy of 213 MeV. The analysis of γ-γ coincidences, which were detected using the EUROGAM detector array, has revealed two new structures at excitation energies above 6 MeV and at moderate spin. The first one could be interpreted as a manifestation of a band termination phenomenon while the second one is associated with a single-particle decay mode.

Recent results from digital INGA at BARC–TIFR Pelletron Linac Facility and future plans

An experimental campaign aimed at studying various high spin phenomena using the Indian National Gamma Array (INGA) at the BARC–TIFR Pelletron Linac Facility has been successfully completed. The array consisting of a large number of Compton-suppressed clover detectors was coupled to a digital data acquisition system with 96 channels. The present system provides higher throughput, better energy resolution and better stability of gain for the multidetector Compton-suppressed clover array compared to its previous conventional system with analog shaping. Selected results from this array are discussed which highlight the exotic shapes, novel excitation modes and interesting isomers of the nuclei. The preliminary results from the experimental efforts to improve the sensitivity and capability of the array by adding ancillary detectors are also described briefly.

Triaxial projected shell model study of chiral rotation in odd–odd nuclei

Chiral rotation observed in 128Cs is studied using the newly developed microscopic triaxial projected shell model (TPSM) approach. The observed energy levels and the electromagnetic transition probabilities of the nearly degenerate chiral dipole bands in this isotope are well reproduced by the present model. This demonstrates the broad applicability of the TPSM approach, based on a schematic interaction and angular-momentum projection technique, to explain a variety of low- and high-spin phenomena in triaxial rotating nuclei.

Nuclear structure in odd-odd nuclei,144<~A<~194

A comprehensive review of the present understanding, both theoretical and experimental, of intrinsic and rotational level structures in medium-heavy deformed odd-odd nuclei is presented. A discussion of the various experimental methods is presented, emphasizing the need for a variety of experimental approaches. The odd-odd nuclei that are immediately amenable to fruitful additional study are pointed out. A discussion of the intrinsic level structures, Gallagher-Moszkowski (GM) splittings, Newby (N) shifts, and role of the residual $p\ensuremath{-}n$ interaction is presented. Currently available data in the rare-earth region allow the empirical determination of 137 GM splittings and 36 N shifts for 25 odd-odd nuclei in the mass region 152\ensuremath{\leqslant}$A$\ensuremath{\leqslant}188. A new parametrization of the residual $p\ensuremath{-}n$ interaction is presented which also takes into account the 27 GM splittings and 12 N shifts from the actinide region. Newly discovered features of rotational bands, such as odd-even staggering, and other high-spin phenomena, such as signature inversion and delay in bandcrossing frequency, are discussed. The role of higher-order Coriolis coupling is pointed out. Systematics of the two-quasiparticle excitations, shape coexistence, isomers, and four-quasiparticle states are presented. Calculated results of the two-quasiparticle intrinsic excitations using two methods, the intrinsic level spacings for odd-A neighboring nuclei and the quasiparticle-plus-phonon coupling model, are compared with experiment.

High spin spectroscopy with the projected shell model

We review recent applications of the projected shell model to the high spin spectroscopy. In particular, various high spin phenomena related to band crossing and signature dependence, for which the standard cranked shell model encounters difficulties, are extensively discussed.

High-spin phenomena in 174Os

High-spin states of 174Os have been investigated by means of the 146Nd( 32S,4n) 174Os reaction using the ESSA30 multidetector system. The decay is dominated by the ground-state positive-parity band, two negative-parity 4 − and 5 − bands and another band starting at spin 9. Deformed shell-model calculations have been carried out to interpret the observed band structures. The role of the strongly shape-driving, non-aligned, π h 9 2 configuration in the low-spin region of the ground-state band is discussed. The first band crossing is interpreted as due to the ν i 13 2 alignment. The two lowest side-bands are understood in terms of coupling to octupole excitations.

High-spin phenomena in atomic nuclei

A description of high-spin phenomena in atomic nuclei is presented from both the experimental and theoretical points of view. The characteristic features of collective nuclear motion, such as rotational bands, band crossings, and backbending, as well as noncollective aspects, like high-spin isomers and irregular decay patterns, are discussed in detail. Recent achievements of the cranking model including the independent quasiparticle and the shell correction methods are reviewed. Changes in the structure of nuclei excited up to the highest possible angular momenta are analyzed; in particular, angular momentum alignment effects, shape changes, possible phase transitions, and sudden rearrangements in the single-particle structure are discussed. Phenomena related to the nuclear quasicontinuum spectra are also examined.

Strength of the Qπ · Qν interaction and the strong-coupled pseudo-SU(3) limit

The suitability of pseudo SU(3) strong coupled wave functions in representing the normal parity part of yrast eigenstates of systems with protons and neutrons filling different major shells and interacting with one another via a Q π · Q ν interaction is explored. In addition, we find that the overlaps of yrast eigenstates of H with the leading SU(3) symmetry follow the correlation of Q · Q with H very closely and are large even when Q π · Q ν contributes less than half to the full width of the eigenvalue spectrum of H. The results sugges that the pseudo-SU(3) coupling scheme will prove useful in microscopic shell-model studies of high-spin phenomena in rare earth and actinide nuclei.

Microscopic look at backbending

A shell-model calculation of high-spin phenomena in the highly neutron deficient Ba-Ce-Nd region is reported. An inert spherically symmetric $Z=50=N$ core is assumed with extracore nucleons distributed among the ${g}_{\frac{7}{2}}$, ${d}_{\frac{5}{2}}$, ${d}_{\frac{3}{2}}$, ${s}_{\frac{1}{2}}$ normal-parity orbitals and the unique parity ${h}_{\frac{11}{2}}$ orbital with the number of particles within each set fixed. The normal-parity subspace is further truncated to a single irreducible representation of pseudo SU(3) made effective through the mapping $({g}_{\frac{7}{2}}{d}_{\frac{5}{2}}{d}_{\frac{3}{2}}{s}_{\frac{1}{2}})\ensuremath{\rightarrow}({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{f}}_{\frac{7}{2}}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{f}}_{\frac{5}{2}}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{p}}_{\frac{3}{2}}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{p}}_{\frac{1}{2}})$. A five-dimensional quasispin classification is used for the unique-parity ${h}_{\frac{11}{2}}$ space which is restricted to states with seniority zero and two. Using a surface delta interaction we are able to reproduce the observed backbending in $_{56}^{126}\mathrm{Ba}_{70}$. The model affords a microscopic look at Coriolis antipairing and pair realignment phenomena.