I. Ray

Characteristics of a Compton suppressed Clover detector up to 5 MeV

The Clover detectors in their addback mode are excellent tools for detecting high-energy gamma rays ðX2 MeVÞ: The characteristics ofthese detectors, at energies above 2 MeV ; are usually determined from simulation data or from extrapolation ofthe empirical data. This is the first time that the characteristics ofa Compton suppressed Clover germanium detector have been studied up to 5 MeV using a radioactive 66 Ga ðT1=2 ¼ 9:41 hÞ source. r 2002 Elsevier

Band structure of 79Br

Abstract High-spin states of 79Br have been studied in the reaction 76 Ge( 7 Li , 4nγ) at 32 MeV. A gamma-detector array with twelve Compton-suppressed HPGe detectors was used. The positive-parity yrast states, interpreted as a rotationally aligned g 9 2 proton band, and the negative-parity ground state band have been extended to spins of ( 33 2 + ) and ( 25 2 − ), respectively. Lifetime measurements indicate that both bands have a similar quadrupole deformation of β2 ∼ 0.2. The positive-parity α = −1 2 band has been identified. Several new inter-band transitions are observed. A cranked-shell model analysis shows that the νg 9 2 alignments occur in the positive-parity and the negative-parity bands at rotational frequencies of ℏω ∼ 0.6 and 0.4 MeV, respectively. The level energies and the electromagnetic properties of the g 9 2 band can be well reproduced by a particle-rotor model calculation with an axially symmetric core.

Structure of positive-parity yrast band in 80 Br

Abstract The states of the positive-parity yrast band in 80 Br have been investigated using the 76 Ge( 7 Li, 3n γ ) reaction at a beam energy of 32 MeV. The band has been extended up to 4450 keV with a spin of (14 + ). Unambiguous spin assignments are made for states up to 2944.0 keV and γ -ray multipole mixing ratios are determined for several ΔJ=1 transitions. Lifetimes studies for the 10 + , 11 + and 12 + states provide an estimate of the quadrupole deformation in this band. Cranking model analysis of the experimental data reveals a signature inversion at a spin of 12 ℏ and a probable neutron alignment at ℏω≈0.7 MeV. The results are discussed within the framework of the systematics of similar bands in the lighter Br isotopes and the cranked-shell model. In addition, a new positive-parity and two negative-parity sequences have been identified.

Shape coexistence inHo153

The high-spin states in 153Ho, have been studied by 139 57 La(20Ne, 6n) reaction at a projectile energy of 139 MeV at Variable Energy Cyclotron Centre (VECC), Kolkata, India, utilizing an earlier campaign of Indian National Gamma Array (INGA) setup. Data from gamma-gamma coincidence, directional correlation and polarization measurements have been analyzed to assign and confirm the spins and parities of the levels. We have suggested a few additions and revisions of the reported level scheme of 153Ho. The RF-gamma time difference spectra have been useful to confirm the half-life of an isomer in this nucleus. From the comparison of experimental and theoretical results, it is found that there are definite indications of shape coexistence in this nucleus. The experimental and calculated lifetimes of several isomers have been compared to follow the coexistence and evolution of shape with increasing spin.

Experimental study of the 2p-2h band in {sup 111}Sn

The {delta}I=2 intruder band in {sup 111}Sn, built upon the 4074.3 keV state, was studied. The states were populated in the {sup 100}Mo({sup 20}Ne, {alpha}5n) reaction at a beam energy of 136 MeV. Mean lifetimes of five states up to 8737.2 keV (spin 43/2{sup -}) have been measured for the first time using the Doppler shift attenuation method. In addition, an upper limit of mean lifetime has been estimated for the 9860.0 keV (spin 47/2{sup -}) state. The B(E2) values, derived from the present lifetime results, indicate a quadrupole deformation of {beta}{sub 2}=0.28{+-}0.02 for the 31/2{sup -} state and decrease progressively with spin, suggesting a reduction in collectivity. The dynamic moment of inertia for the band also decreases continuously up to the highest observed frequencies. These results, along with the predictions of a total Routhian surface calculation, suggest that the {delta}I=2 band in {sup 111}Sn undergoes a change of shape from collective prolate to triaxial with increase in spin and possibly terminates in a noncollective oblate state at a high spin.

Evidence for shape coexistence in 77Br

Abstract The nucleus 77 Br has been studied in the reaction 65 Cu( 16 O, 2p2n) at E =75 MeV. Lifetimes have been measured for several states using the Doppler-shift attenuation technique. The B (E2) values for the inband transitions, deduced from the lifetime results, reflect strong collectivity for both the positive-parity yrast band (band 1) and the ground-state negative-parity band (band 2). States with spin above 17/2 + in band 1 are found to have a large average quadrupole deformation of β 2 =0.35. The experimental results for band 2 suggest that the 25/2 − and 29/2 − states are somewhat more strongly deformed than the lower-spin states. A comparison of the experimental results with particle-rotor-model calculations provides evidence for shape coexistence in 77 Br, favouring a prolate shape for the g 9/2 yrast band and an oblate shape for the lowest negative-parity band.