PARTICLE EXCITATIONS AND COLLECTIVITY IN THE N=48 NUCLEI AND BR-83 AND RB-85

Excited states of the nuclei Br-83 and Rb-85 were populated in the rea ctions Se-82(Li-7,alpha 2n) and Se-82(Li-7,4n), respectively, using th e Li-7 beams of the FN tandem accelerator in Cologne (E = 32 MeV) and of the 120 cm cyclotron in Rossendorf(E = 35 MeV). Gamma-gamma-particl e coincidences were measured with six Ge and fourteen Si detectors ins talled at the detector array Cologne OSIRIS CUBE. This technique enabl ed a reaction channel selection. Multipole orders of the gamma-rays we re derived from directional correlations of coincident gamma-rays and from angular distributions. Mean lifetimes were deduced for seven leve ls in Br-83 and two levels in Rb-85 using the Doppler-shift-attenuatio n method. The level scheme of Br-83 has been extended up to (21/2(+)) and 15/2(-) states. In Rb-85 a level sequence built on the ground stat e has been established up to 15/2((-)) and a new cascade of fast M1 tr ansitions 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 t he shell model. The calculations performed in the model space pi(0g(9/ 2), 1p(1/2), 1p(3/2), 0f(5/2)) nu(Og(9/2), 1p(1/2)) reproduce single-p article characteristics as well as collective properties of the level sequences.