A. Dhal

Shape coexistence and high spin states in {sup 52}Cr

High spin states in {sup 52}Cr have been populated by means of the reaction {sup 27}Al({sup 28}Si,3p){sup 52}Cr at a beam energy of 70 MeV and studied with an array, consisting of eight Compton-suppressed clover germanium detectors. Eleven new {gamma} rays have been assigned to {sup 52}Cr and placed in the level scheme. The level structure of {sup 52}Cr has been extended up to E{sub x}{approx_equal}10 MeV. Spins and parities have been assigned to many of the levels on the basis of directional correlations and linear polarization measurements. The band structures are discussed in the framework of cranked Woods-Saxon and deformed Hartree-Fock (HF) models. Both the oblate and prolate orbits are considered for J projection in the HF model. The K=0{sup +} band is properly understood if we consider the J projection from both prolate and oblate orbits and collectivity shown by the K=4{sup +} band to be accounted for by taking the J projection from prolate HF configurations. Thus there is prolate and oblate shape coexistence in {sup 52}Cr.

Indian National Gamma Array at IUAC

Indian National Gamma Array (INGA) is a 4π multi-detector gamma-ray spectrometer based on twenty four Compton-suppressed Clover Germanium detectors with a total photo peak efficiency ~ 5 %. INGA was designed to perform high resolution gamma-ray spectroscopy to study nuclear structure at high spins with stable ion beams at Inter University Accelerator Centre (IUAC). Description of the facility and performance of the array are presented in this paper. Since its commissioning, a number of nuclear spectroscopic investigations have been carried out using the array.

High Spin Spectroscopy and Shape Evolution in 105 Cd

High spin states in 105Cd were studied using 16O beam on 92Mo reaction at an incident beam energy of 75 MeV. The level scheme of 105Cd has been observed up to an excitation energy of 10.8 MeV with the addition of 30 new gamma transitions to the previous work. Spin and parity for most of the reported levels are assigned from the DCO ratios and linear polarization measurements. The microscopic origin of the investigated band structures is discussed in the context of triaxial projected shell model. The energies of observed positive and negative parity bands agree with the predictions of the TPSM by considering triaxial deformation for the observed excited band structures. The shape evolution with increasing angular momentum is explained in the framework of Cranked Shell Model and the Total Routhian Surface calculations.

Band structure and shape coexistence in {sub 56}{sup 135}Ba{sub 79}

Excited states of {sub 56}{sup 135}Ba{sub 79} at high spins are studied using the reaction {sup 130}Te({sup 9}Be,4n){sub 56}{sup 135}Ba{sub 79} at 42.5-MeV beam energy. The earlier known level scheme is extended up to 6.4-MeV excitation energy and (37/2)(Planck constant/2pi) spin with the addition of several transitions. We have performed polarization asymmetry measurements for some of the strong transitions by using a Clover detector to assign the parity. A comparison of experimental data with the results of tilted axis cranking calculations based on various configurations indicates the coexistence of multiple minima in the triaxial deformation (gamma), whereas axial symmetric deformation (epsilon{sub 2}) remains constant around 0.09.

High spin states in {sup 139}Pm

The odd mass nucleus {sup 139}Pm has been studied to high spins through the {sup 116}Cd({sup 27}Al,4n){sup 139}Pm reaction at an incident beam energy of 120 MeV. The de-exciting {gamma}-rays were detected using an array of 12 Compton suppressed Ge detectors. A total of 46 new levels have been proposed in the present work as a result of the observation of 60 new {gamma}-rays. Four new bands including a {delta}J=1 sequence have been identified and all the earlier reported bands, other than the yrast band, have been extended to higher spins and excitation energy. The spin assignments for most of the newly reported levels have been made using the observed coincidence angular anisotropy. Tilted axis cranking calculations support the interpretation of two of the observed magnetic dipole sequences as examples of magnetic rotational bands.

Shape evolution of the highly deformed {sup 75}Kr nucleus examined with the Doppler-shift attenuation method

High-spin states of the {sup 75}Kr nucleus have been populated via the {sup 50}Cr({sup 28}Si,2pn){sup 75}Kr reaction at an incident beam energy of 90 MeV. Lifetimes of nine states up to spin I=33/2 for the positive-parity band and seven states up to I=27/2 for the negative-parity band have been measured using the Doppler-shift attenuation method. The deduced transition quadrupole moments Q{sub t} of these bands have been compared to the projected shell-model calculations to gain insight into the evolution of collectivity for the two experimentally studied bands in {sup 75}Kr.

Triaxial shape coexistence and new aligned band in {sup 178}Os

High spin states in {sup 178}Os were studied by means of {sup 165}Ho({sup 20}Ne,p6n){sup 178}Os fusion evaporation reaction at a beam energy of 150 MeV, using a clover detector array. Several new transitions belonging to {sup 178}Os were placed in a level scheme and a new aligned rotational band was observed in addition to earlier known bands. Spin-parity assignments for most of the proposed levels were made using the deduced directional correlation orientation and polarization measurements for the de-exciting transitions. Experimental results are compared with the projected angular momentum deformed Hartree-Fock model calculations and cranked Woods-Saxon model calculations. This nucleus is predicted to be prolate deformed in the ground state but the {gamma}-softness at higher excitation is revealed by the cranked Woods-Saxon model and the geometrical asymmetric model calculations.

HIGH SPIN STATES IN 139Pm

The odd mass nucleus 139 Pm has been studied to high spins through the 116 Cd( 27 A1,4n) 139 Pm reaction at an incident beam energy of 120 MeV. The de-exciting γ-rays were detected using an array of 12 Compton suppressed Ge detectors. A total of 46 new levels have been proposed in the present work as a result of the observation of 60 new γ-rays. Four new bands including a ΔJ = 1 sequence have been identified and all the earlier reported bands, other than the yrast band, have been extended to higher spins and excitation energy. The spin assignments for most of the newly reported levels have been made using the observed coincidence angular anisotropy. Tilted axis cranking calculations support the interpretation of two of the observed magnetic dipole sequences as examples of magnetic rotational bands.