Arun Bharti

Microscopic study of deformation systematics and low-lying yrast spectra in even-even ruthenium isotopes

Abstract The yrast spectra with J max π = 10 + and the observed systematics of the low-lying states in 94–112 Ru nuclei are examined by carrying out Hartree-Fock-Bogoliubov calculations employing a pairing-plus-quadrupole-quadrupole effective interaction operating in a reasonably large valence space outside the 76 Sr core. Our calculations reveal that the systematics of the low-lying yrast states in 94–112 Ru are intricately linked with the deformation-producing tendency of np interaction when operating between spin-orbit partner (SOP) orbits. Our results indicate that such systematics depend crucially on the simultaneous increase of the relative occupation probabilities of ( d 5 2 ) π −( d 3 2 ) v and ( g 9 2 ) π −( g 7 2 ) v SO

E2 transition and QJ+ systematics of even-mass ruthenium nuclei

The yrast spectra with Jmaxpi = 10+, B(E2) transition probabilities and QJ+ values are calculated for even-even ruthenium isotopes by carrying out variation after projection (VAP) calculations in conjunction with the Hartree-Fock-Bogoliubov (HFB) ansatz employing a pairing-plus-quadrupole-quadrupole effective interaction operating in a reasonably large valence space outside the 76Sr core. Our calculations describe the shape changes as a function of mass number for ruthenium isotopes and also reveal that both the HFB technique as well as the quadrupole-plus-pairing-quadrupole model of the two-body interaction are fairly reliable in this mass region.

A MICROSCOPIC PERSPECTIVE ON STRUCTURE OF YRAST BANDS IN 100-112Ru ISOTOPES

The projected shell model (PSM) study of 100-112Ru nuclei is carried out. The reliability of the ground state wave functions is checked by reproducing yrast spectra and electromagnetic properties. The results of calculations indicate that the observed deformation systematics in 100-112Ru isotopes depends on the increase of occupation probability of (1h11/2)ν orbit and the deformation producing tendency of n–p interaction operating between spin orbit partner (SOP) orbits (d5/2)π-(d3/2)ν and (g9/2)π-(g7/2)ν. Besides this, the results on band diagrams show that the yrast spectra in Ru isotopes do not arise from a single intrinsic state only but also from multi-quasiparticle states.

THEORETICAL INVESTIGATION OF POSITIVE PARITY BAND STRUCTURE OF Y AND Nb ISOTOPES

The positive parity band structure of odd mass neutron-rich 97–103Y and 99–105Nb nuclei has been studied using microscopic technique known as the projected shell model (PSM) with the deformed single-particle states generated by the standard Nilsson potential. The nuclear structure properties like yrast spectra, energy splitting, moment of inertia, rotational frequencies and reduced transition probabilities B(M1) and B(E2) have been calculated and their comparison with the available experimental data has been made. A shape evolution has also been predicted in these isotopes as one moves from 97Y to 99Y and 99Nb to 101Nb. The PSM calculations also demonstrate the multi-quasiparticle structure in these nuclei.

Theoretical study of neutron-rich 107,109,111,113Rh isotopes

A theoretical study of the structure of some odd mass Rh nuclei in the A ~ 100 mass region is carried out by using the angular momentum projection technique implemented in the projected shell model (PSM). The influence of the high-j orbitals (h11/2 for neutrons and g9/2 for protons) on the structure of 107–113Rh isotopes is investigated in the present case by assuming an axial symmetry in the deformed basis. For these isotopes, the structure of multi-quasi-particle qp bands is studied along the yrast line in detail. Further, the phenomenon of back-bending is also studied theoretically and is found to be in agreement with the experimental data. The reduced transition probabilities, i.e., B(E2) and B(M1) for the yrast band are also obtained from the PSM wave functions for the first time, thereby providing an opportunity for the experimentalists to work for this data.

MICROSCOPIC STUDY OF NEGATIVE PARITY YRAST STATES IN NEUTRON-DEFICIENT 119–127Ba ISOTOPES

The negative parity yrast bands of neutron-deficient 119–127Ba nuclei are studied by using the Projected Shell Model approach. Energy levels, transition energies and B(M1)/B(E2) ratios are calculated and compared with the available experimental data. The calculations reproduce the band head spins of negative parity yrast bands and indicate the multi-quasiparticle structure for these bands.

Theoretical investigation of nuclear structure properties of 144Gd, 146Dy and 148Er isotones

Some N=80 isotones (144Gd, 146Dy and 148Er) have been studied by using the HFB framework and the nuclear structure properties like yrast spectra, subshell occupation numbers and quadrupole moments have been obtained. Intrinsic quadrupole moments obtained from HFB calculations show a gradual increase as one moves from 144Gd to 148Er indicating, thereby, an increase in deformation, which is in agreement with the experimental results. From the results of subshell occupation numbers, it is clear that subshells 3s1/2, 2d3/2, 2d5/2, 1g7/2 and 1h11/2 of protons are contributing towards the development of deformation as one moves from 144Gd to 148Er.

Study of odd mass 115−125Sb isotopes with the projected shell model calculations

The projected shell model (PSM) with the deformed single-particle states, generated by the standard Nilsson potential, is applied to study the negative-parity high spin states of 115–125Sb nuclei. The nuclear structure quantities like band structure and back-bending in moment of inertia have been calculated with PSM method and are compared with the available experimental data. In addition, the reduced transition probabilities, i.e., B(E2) and B(M1), are also obtained for the yrast band of these isotopes for the first time by using PSM wave function. A multi-quasiparticle structure has been predicted for 115–125Sb isotopes by the present PSM calculations.

Study of yrast structures in 55,57Cr

The characteristic nuclear structure properties of yrast bands of 55,57Cr have been investigated by using two body effective interactions incorporated in phenomenological axial framework. In order to check the validity of the chosen framework as well as chosen valence space, the calculated results are compared with the available experimental data and a good agreement has been found from the comparison. The back-bending in moment of inertia has also been studied and attributed to the alignment of odd g9/2 neutron along the rotation axis.

Theoretical study of band structure of odd-mass 115,117I isotopes

By using the microscopic approach of Projected Shell Model (PSM), negative-parity band structures of odd mass neutron-rich 115,117I nuclei have been studied with the deformed single-particle states generated by the standard Nilsson potential. For these isotopes, the band structures have been analyzed in terms of quasi-particles configurations. The phenomenon of back bending in moment of inertia is also studied in the present work.