STATES OF SENIORITY-3 AND SENIORITY-5 IN THE N=48 NUCLEUS Y-87

Excited states of the nucleus Y-87 were investigated via the reaction Se-80(B-11,4n) at 45 MeV. gamma rays were detected with the six-detect or array OSIRIS CUBE. The level scheme of Y-87 has been extended up to J(pi) = 33/2((-)) at E approximate to 7 MeV. Mean lifetimes of eight levels have been deduced using the Doppler-shift-attenuation method. T he structure of Y-87 has been interpreted in terms of the shell model. The calculations performed in the model space pi(0f(5/2),1p(3/2),1p(1 /2),0g(9/2)) nu(1P(1/2), 0g(9/2)) well reproduce experimental excitati on energies and transition strengths in Y-87, especially the large B(M 1) values of up to 1.8 W.u. between yrast states with J >21/2. Structu ral differences between Y-87 and the isotone Rb-85,discussed on the ba sis of the shell-model calculations.