Evidence for shape coexistence from few-quasiparticle excitations in 83Kr

Abstract

Excited states in 83Kr were studied in the 82Se(α, 3n) reaction using in-beam γ-ray spectroscopy. Measurements of γγ coincidences, excitation functions, angular distributions and linear polarization of the γ-rays were carried out and levels were established up to I = 29 2 . Most of the levels above 2.5 MeV could be grouped into 3 band-like sequences. Lifetimes or limits of lifetimes were determined for 8 members of these bands using the DSA method. The positive-parity 3qp band, I = 21 2 to 29 2 , indicates a prolate deformation similar to the corresponding band in 81Kr. In contrast, only low collectivity was found for a ΔI = 2 sequence built on the 17 2 − yrast state and reaching up to I = ( 29 2 ) . From similarities of the level spacings with the ground state bands and 2qp bands of the even-mass neighbours, the 3qp configuration ν( g 9 2 ) −2ν p 1 2 is proposed for this sequence. Another band, comprising levels with I π = 13 2 − to ( 27 2 −) in a ΔI = 1 sequence, displays a sharp decrease of the intraband M1 transition rates with increasing spin.