Particle excitations and collectivity in the N = 48 nuclei 83Br and 85Rb

Abstract

Excited states of the nuclei 83Br and 85Rb were populated in the reactions 82Se( 7Liα2n) and 82Se( 7Li,4n), respectively, using the 7Li beams of the FN tandem accelerator in Cologne ( E = 32 MeV) and of the 120 cm cyclotron in Rossendorf ( E = 35 MeV). Gamma-gamma-particle coincidences were measured with six Ge and fourteen Si detectors installed at the detector array Cologne OSIRIS CUBE. This technique enabled a reaction channel selection. Multipole orders of the γ-rays were derived from directional correlations of coincident γ-rays and from angular distributions. Mean lifetimes were deduced for seven levels in 83Br and two levels in 85Rb using the Doppler-shift-attenuation method. The level scheme of 83Br has been extended up to ( 21 2 + ) and 15 2 − states. In 85Rb a level sequence built on the ground state has been established up to 15 2 ( −) and a new cascade of fast M1 transitions starting with a 17 2 ( −) state at 3198.2 keV has been found. Furthermore, several medium-spin states have been newly introduced. The level sequences in both nuclei have been interpreted in terms of the shell model. The calculations performed in the model space π(0 g 9 2 , 1 p 1 2 , 1 p 3 2 , 0 f 5 2 ) ν(0 g 9 2 , 1 p 1 2 ) reproduce single-particle characteristics as well as collective properties of the level sequences.