Shape Evolution in Ho and Dy Isotopes Around 150 160

Abstract

newline Motivated by the rich varieties of structural features of nuclei in the rare earth region, the newlineaim of the thesis was set to investigate the nuclear structure properties of nuclei around A newline~ 150 and A ~ 160. Data acquired in three In-beam experiments using Indian National newlineGamma Array (INGA) have been analysed and new results for level scheme and level newlinelifetime are obtained. A decay spectroscopy experiment has also been done to measure newlinelevel lifetimes. The thesis first reviews briefly some of the relevant results of investigation on newlinestructural properties of nuclei of the rare earth region that built up the motivation behind newlinethe present research works. The excited states of odd-odd 154Ho nucleus have been studied by the 141Pr(16O,3n) 154Ho reaction at Elab= 82 MeV utilising the Indian National Gamma Array setup at BARC-TIFR Pelletron facility, Tata Institute of Fundamental Research, Mumbai. Data newlinefrom and#947; - and#947; coincidence, directional correlation (DCO), and polarisation measurements newlinehave been analysed to assign and confirm the spins and parities of the levels. The reported newlinelevel scheme of 154Ho has been improved by including new levels and transitions. Mixing newlineratios for the mixed transitions extracted from DCO ratios and parity assignments from newlinepolarisation data are reported for the first time. The low-lying states in 154Ho, which are newlinemostly collective, characterized by regularity in the excitation spectra, are proposed to be newlinearising from neutron excitation. At higher excitation, there is a transition from collective newlineto single-particle character, accompanied by the appearance of irregular and complex newlinestructure caused by proton excitation. The newly identified E1 gamma transitions newlineconnecting the low-lying positive and negative parity bands indicate octupole correlation newlinein 154Ho. These new connections also support the phenomenological analysis to interpret newlinethe observed experimental features from a different perspective. The low-lying levels of well - deformed 160Dy nucleus (and#946;2= 0.3360(13)) have been popula