Multiplet structure and core-related effects on transition rates in87Y and neighbouringA≈ 90 nuclei

Bombarding a85Rb target by 27 MeVα-particles the following half-lives of excited states in different nuclei have been determined by means of the generalized controid shift method: in87Y,T1/2(2827.1 keV)=0.75±0.10 ns,T1/2(2675.9 keV)=0.25±0.10 ns,T1/2(3595.3 keV)=0.5±0.2 ns andT1/2(2986.9, 3094.4 keV)<0.1 ns; in88Y,T1/2(232.1 keV)=0.8±0.1 ns and in85Rb,T1/2(151.2 keV)=0.6±0.1 ns. In87Y, the members of the doublet (vg 9 2/−2 )8+ (πp1/2) are identified. E2 transition rates 21/2+⇒ 17/2+ in odd A≈ 90 nuclei are shown to represent essentially core transitions. Evidence for the existence of seniority-five configurations is found.