Two previously known bands in the excitation scheme of the 154 Tb nucleus have been investigated for the multipolarity and the electric/magnetic nature of the intra- and inter-band transitions. The excited states of the nucleus were populated in an alpha-beam induced reaction and the y-rays emitted therefrom were detected using an array of Compton suppressed HPGe clover detectors. The experimental findings are indicative of a shape evolution of the nucleus and development of strong triaxiality at higher spins. The multipolarities of the inter-band transitions brings forth the same. Total Routhian Surface (TRS) calculations and those in the framework of Triaxial Projected Shell Model (TPSM) have been carried out and the results corroborate the proposition on triaxiality.

Single-particle and collective excitations in 116Sb are studied using the reaction 115In(alpha, 3n) 116Sb at abeam energy of 40 MeV and investigated using gamma -ray spectroscopic techniques. The existing level scheme is extended with the observation of several new transitions. The previously known band structures are extended to higher spins. Measurements of the directional correlation from oriented states (DCO) ratio and polarization asymmetry of the observed gamma rays are carried out to assign the spin-parities of the excited levels, populated in the present work. New band structures are interpreted as being due to the coupling of the valence particles with the 2p-2h intruder states of the Sn core. Further, the collective band structures are discussed on the basis of their rotational properties, total Routhian surface calculations, and the triaxial projected shell model approach.

It is demonstrated that the Triaxial Projected Shell Model reproduces the energies and transition probabilities of the nucleus 104Ru and the rigid triaxial nucleus 112Ru. An interpretation in terms of band mixing is provided.

The positive and negative parity rotational band structures of odd-odd Nb isotopes with atomic masses 90, 92 and 94 are investigated using the theoretical framework of the projected shell model. These odd-odd nuclei are found to be ideal for investigating the significant structural changes occurring in the region situated far from the valley of stability. This is the first time that such comprehensive theoretical data for both positive and negative parities together for the odd-odd 90-94Nb isotopes have been disclosed. The g-factor and electromagnetic transition probabilities are among the various nuclear structure quantities that are examined for the first time. Using a broad configuration space for both protons and neutrons, the computed data have been anticipated up to high spin values.

A positive parity sequence of ΔI=2 γ transitions has been identified above Iπ=9/2+ state (Ex=2019 keV) in 115Sb through in-beam γ ray spectroscopic technique. Rotational features of this sequence are found similar to a low-K decoupled band. Observation of this newly identified low-K decoupled band, along with the earlier reported strongly coupled high-K band in this nucleus, provides the first experimental evidence for prolate-oblate shape coexistence associated with g9/2 proton-hole configuration around Z=50 shell closure. Experimental results are reproduced reasonably well in the frameworks of the projected shell model and the total Routhian surface calculations.

An experimental investigation of ^105Pd has revealed, for the first time, the existence of two wobbling bands both having one phonon configuration and originating from the coupling of the wobbling phonon to the ground state band and to its signature partner. The doublet one-phonon wobbling bands are, in turn, found to be the signature partner bands. These observations have been drawn from the measured ratios of the inter-band and intra-band gamma transition rates. The model calculations based on the triaxial projected shell model (TPSM) approach have been performed and are found to be in good agreement with the experimental observations. These calculations provide an insight into the nature of the observed structures at a microscopic level.

The energies and B ( E 2) transitions involving the states of the ground- and γ -bands in thirty transitional and deformed nuclei are calculated using the triaxial projected shell model (TPSM) approach. Systematic good agreement with the existing data substantiates the reliability of the model predictions. The Gamma-rotor version of the collective Bohr Hamiltonian is discussed in order to quantify the classification with respect to the triaxial shape degree of freedom. The pertaining criteria are applied to the TPSM results and the staggering of the energies of the γ -bands is analyzed in detail. An analog staggering of the intra- γ B(E2, I → I-2) is introduced for the first time. The emergence of the staggering phenomena in the transitions is explained in the terms of interactions between the bands.

The majority of atomic nuclei have deformed shapes and nearly all these shapes are symmetric with respect to reflection. There are only a few reflection asymmetric pear-shaped nuclei that have been found in actinide and lanthanide regions, which have static octupole deformation. These nuclei possess an intrinsic electric dipole moment due to the shift between the center of charge and the center of mass. This manifests in the enhancement of the electric dipole transition rates. In this article, we report on the measurement of the lifetimes of the high-spin levels of the two alternating-parity bands in 100Ru through the Doppler shift attenuation method. The estimated electric dipole transition rates have been compared with the calculated transition rates using the triaxial projected shell model without octupole deformation and are found to be an order of magnitude enhanced. Thus, the observation of seven interleaved electric dipole transitions with enhanced rates establish 100Ru as possibly the first octupole deformed nucleus reported in the A ti 100 mass region.

A systematic investigation of the wobbling band structures observed in odd-mass nuclei of $^{161,163,165,167}$Lu, $^{167}$Ta $^{131}$Cs, $^{135}$Pr, $^{151}$Eu, $^{183}$Au, $^{133}$Ba, $^{105}$Pd, $^{133}$La, $^{187}$Au and $^{127}$Xe is performed using the triaxial projected shell model (TPSM) approach. It is demonstrated that all the studied band structures have transverse wobbling mode, except for $^{133}$La, $^{187}$Au (negative parity), $^{183}$Au (positive parity) and $^{127}$Xe nuclei where the wobbling frequency increases with spin, indicating that the collective motion has a longitudinal character. To elucidate further the wobbling nature of the band structures, electromagnetic transition probabilities have been evaluated and it is observed that inter-band transitions are dominated by $E2$ rather than $M1$ as expected for a typical signature partner band. It is shown that TPSM approach provides a reasonable description of all the measured properties of the studied nuclei.

High spin states in the 96Tc nucleus were populated in the As-75(Si-28, 4p3n) fusion-evaporation reaction at E lab = 120 MeV and the de-excitations were investigated through in-beam gamma-ray spectroscopic techniques using indian national gamma array spectrometer consisting of 18 clover Ge detectors. The present level scheme of the Tc-96 nucleus has been extended substantially with the addition of about forty five new gamma transitions. The level structures in Tc-96 have been established up to excitation energy similar to 10 MeV and angular momentum similar to 25PLANCK CONSTANT OVER TWO PI. Level structures of 96Tc nucleus are discussed in the framework of triaxial projected shell model calculations.

A comprehensive analysis of high spin band structures for odd mass ^117-127 I nuclei is performed using Triaxial Projected Shell Model (TPSM) approach. Using suitable values for the relevant parameters, the estimated energy spectrum of odd mass ^117-127 I agrees well with the experimental results The potential energy surfaces reveal that the isotopes are heading from γ -softness towards rigidity. The current analysis further revealed that the typical band crossing along the yrast as well as the yrare line is caused by the three-quasipaticle band crossing the one-quasiparticle band. Further, transitional probabilities [B(E2) and B(M1)] have been computed and found to be consistent with the available experimental data. Chirality in ^123 I has also been discussed.

The normal deformed bands of [Formula: see text]Lu isotopes have been studied by using projected shell model approach. The band head spins, configurations and energies of all the normal deformed bands are reproduced well by the above said approach. The present calculations have predicted [Formula: see text] band head spin for [523]7/2 − bands of [Formula: see text]Lu. The observed systematics of aligned angular momenta and the experimental differences in frequencies around the backbends for all the normal deformed bands are reproduced well by the theoretical results. Besides this, the observed backbends or upbends in these isotopes may be ascribed to the alignment of a pair of neutrons in the neutron [Formula: see text] orbital. Although the theoretical [Formula: see text] values obtained from the projected shell model wavefunctions overestimate the experimental [Formula: see text] values in [Formula: see text]Lu, yet they are close to the measured values, considering the precision of measurement. The reduction in the theoretical [Formula: see text] values around the band crossing region may be ascribed to change in nuclear structure of yrast bands due to neutron pair alignment in [Formula: see text] orbital.

A systematic study on the structural evolution induced by the change in neutron number as well as by the increase in angular momentum for even-even 160−178 Yb isotopes has been made using the triaxial projected shell model (TPSM). A detailed analysis of γ-vibrational bands built on ground state has been presented in addition to the yrast band for these nuclei in the present study. The structural changes arising with the increase in neutron number have been quite extensively explained with the help of some interesting nuclear phenomenon. The characteristics of energy ratio and staggering parameter indicate the shape evolution from γ-soft to rigid rotational nuclei as one moves from 160 to 178 Yb. Additionally, the calculated electric quadrupole reduced probabilities B(E2), both in-band and inter-band, and gyro-magnetic factors present a reasonably good agreement with the experimental results.

The projected shell model has been employed to study the energy levels and alignment frequencies of the normally deformed bands of light lutetium isotopes. Band head spins and configurations have been reproduced for all the positive parity bands of 161-165Lu isotopes and negative parity bands of 163Lu. The theoretical aligned angular momenta reasonably reproduced the observed backbends and their corresponding rotational frequencies for all the experimentally observed normally deformed bands. Moreover, I = 7/2- state is predicted as band head spin for negative parity yrast bands of 161,165Lu. The negative parity yrast bands of 161,165Lu are predicted to have 1r 1h11/2[523]7/2- configuration. Further, the calculated B(E2) values of 165Lu show reasonable agreement with the available experimental data. The dip predicted in the B(E2) values may be interpreted due to the alignment of a pair of neutrons in the neutron 1i13/2 orbital of all yrast bands of 161-165Lu. (c) 2022 Elsevier B.V. All rights reserved.

Transverse wobbling was investigated in the 151Eu nucleus by populating the excited states using 148Nd(7Li, 4n)151Eu at a beam energy of 30 MeV. Three new interconnecting transitions have been placed between the two negative parity bands. The M1/E2 character of the interconnecting AI =1 transitions between the negative parity bands was extracted from the mixing ratios using the RDCO and linear polarization method. The spin and parity of the states of different bands have also been assigned. The dominant E2 character of the interlinking transitions between the yrast and first phonon wobbling band and the dominant M1 character between the yrast band and its signature partner band indicate the presence of transverse wobbling in the 151Eu nucleus. It is further demonstrated that the triaxial projected shell model approach describes the observed experimental properties.

Structures of negative parity multi-quasiparticle states in Xe-127 have been investigated through in-beam gamma-ray spectroscopy. Excited states were populated via the Sn-122(Be-9, 4n gamma)Xe-127 fusion-evaporation reaction at E-beam = 48 MeV. Two new negative parity bands have been identified and their structures have been discussed using the triaxial projected shell model (TPSM) approach. One of the bands is established above the I-pi = 27/2(-) state at 3702 keV and based on the experimental inferences and TPSM results, this band is interpreted as a gamma-band built on a three-quasineutron configuration. The second sequence, found above I-pi = 31/2(-) state at 4848 keV, is proposed to have a two-proton aligned configuration (nu h(11/2) circle times pi h(11/2)(2)), considering the properties of this band with the neighbouring isotopes. The analysis of the TPSM wave function substantiates the proposed interpretation of this band.

The microscopic origin of the $γ$-softness (fluctuations in the triaxiality parameter $γ$ of the nuclear shape) observed in atomic nuclei is studied in the framework of the triaxial projected shell model approach, which is based on the deformed mean-field picture with multi-quasiparticle configuration space. It is demonstrated that the coupling to quasiparticle excitations drives the system from a $γ$-rigid to a $γ$-soft pattern. As an illustrative example for a $γ$-soft nucleus, a detailed study has been performed for the $^{104}$Ru nucleus. The experimental energies and a large sample of measured $E2$ matrix elements available for this nucleus are reproduced quite accurately. The shape invariant analysis of the calculated $E2$ matrix elements elucidates the $γ$-soft nature of $^{104}$Ru.

The current work exhibits the effective implementation of the triaxial projected shell model (TPSM) to explore the non–axial features displayed by 82−88 Ge and 66−74 Se isotopes located close to the shell closures at Z = 28 and N = 50.The interaction of excited band structures with the ground state seems to have a profound and considerable impact on the pattern of deformation of these nuclei. The systematic comparison and analysis of the deformation systematics of E ( 2_1^+ ) and R 4/2 ratio reflect the γ -soft nature of the neutron-deficient Se isotopes, whereas neutron-rich Ge isotopes demonstrate a shape transition from spherical to γ -soft nature. The application of TPSM in the present work not only yields the yrast band but also brings forth γ - and 2 γ -vibrational band spectra upto high spins for the first time. To properly comprehend the evolution of intrinsic nuclear structural features of the studied even-even Ge and Se isotopic chains, numerous other nuclear structure properties, such as back-bending in MOI, variation of g-factor with angular momentum, and reduced transition probabilities of γ - and g -band, have also been covered within the deformed triaxial basis. The TPSM results, generated by using the most appropriate values of parameters in the Hamiltonian for studied even-even Ge and Se isotopic chains, are in reasonable accordance with their experimental counterparts as well as other theoretical results.

The triaxial projected shell model (TPSM) approach is generalized to investigate the negative parity band structures in even-even systems. In the earlier version of the TPSM approach, the quasiparticle excitations were restricted to one major oscillator shell and it was possible to study only positive parity states in even-even systems. In the present extension, the excited quasiparticles are allowed to occupy two major oscillator shells, which makes it possible to generate the negative parity states. As a major application of this development, the extended approach is applied to elucidate the negative parity high-spin band structures in $^{102-112}$Ru and it is shown that energies obtained with neutron excitation are slightly lower than the energies calculated with proton excitation. However, the calculated aligned angular momentum ($i_x$) clearly separates the two spectra with neutron $i_x$ in reasonable agreement with the empirically evaluated $i_x$ from the experimental data, whereas proton $i_x$ shows large deviations. Furthermore, we have also deduced the transition quadrupole moments from the TPSM wavefunctions along the negative-parity yrast- and yrare- bands and it is shown that these quantities exhibit rapid changes in the bandcrossing region.

The present work demonstrates the application of multi-quasiparticle triaxial projected shell model (TPSM) to investigate the band structures of 98−106Ru isotopes. These nuclei, falling in the mass region A ~ 100 of nuclear chart, exhibit a variety of interesting properties including the description of band structures with well developed γ- and 2γ-bands. By performing the exact three-dimensional angular-momentum projection technique used in TPSM, a reliable description of yrast and near yrast bands is presented in detail in the present work. The discussion on the importance of 2-quasiparticle neutron bands with K = 1 and K = 3 has proven to be quite substantial in describing various structural properties of these nuclei. It is reported that the comparison of calculations and experiments yields good agreement and a reasonable description of structure variations, transition rates and many other observed properties of isotopes under consideration has been quite systematically provided.