Collective behavior in Rb-78

Mean lifetimes of 10 states in Rb-78 have been measured using the recoil-di stance method. The gamma-ray spectra of the recoils produced following the Ni-58(Na-23,2pn) Rb-78 reaction at 70 MeV were observed in prompt coinciden ce using the FSU plunger in the Pitt-FSU detector array. Different decry cu rves in different coincidence gates provide additional confirmation for the 153 keV doublet in the level scheme. The alternating pattern of B(M1) stre ngths observed previously in the yrast band was seen to continue down to lo wer spins but with an attenuated magnitude, in agreement with neighboring o dd-odd nuclei Br-74 and Y-82 A slight reduction in collectivity with decrea sing spin was inferred in the lowest positive- and negative-parity bands ba sed on the gradual decrease in the B(E2) strengths. Particle-rotor model ca lculations predict strong alternations in both the signature splitting and B(MI) strength pattern in the positive-parity yrast band, in qualitative ag reement with the experimental results. [S0556-2813(98)02812-X].