Investigation of the Low- and Medium-Spin Level Structure in 77As

The low-and medium-spin level structure of 77As nucleus has been investigated using the 76Ge(alpha, p2n) fusion evaporation reaction and the standard in-beam gamma ray spectroscopic technique. The deexciting gamma rays were detected with the Indian National Gamma Array spectrometer comprising Clover and LEPS detectors. The previously known 9/2+ yrast positive-parity band, based on the pi(g9/2) configuration, has been extended to the excitation energy of Ex approximate to 7.5 MeV with J pi = (33/2+). An extension of the high-lying negative-parity band, based on the pi[(g9/2)] circle times nu[(g9/2)(fp)] configuration, has been made up to Ex approximate to 5.1 MeV, J pi = (25/2-). The yrast positive-parity alpha = -1/2 signature partner band has newly been identified and the occurrence of large signature splitting associated with the partner bands have been observed. A quasi-gamma vibrational band structure built on the nonyrast 13/2+ state has also newly been established. The experimental findings have been interpreted on the basis of the predicted results from the total Routhian surface, particle plus triaxial-rotor model, and shell-model calculations. The band crossing phenomena correlated to the nu(g9/2) alignment and the perseverance of triaxial shape up to the highest observed excitation regime of the 9/2+ yrast positive-parity band have been discussed. The evidence for the possible onset of the stapler-like mechanism prevailing in the high-lying negative-parity band structure are presented.