States of seniority 3 and 5 in the N=48 nucleus ⁸⁷Y

Excited states of the nucleus ⁸⁷Y were investigated via the reaction ⁸⁰Se(¹¹B,4n) at 45 MeV. γ rays were detected with the six-detector array OSIRIS CUBE. The level scheme of ⁸⁷Y has been extended up to J^π=33/2^(-) at E≈7 MeV. Mean lifetimes of eight levels have been deduced using the Doppler-shift-attenuation method. The structure of ⁸⁷Y has been interpreted in terms of the shell model. The calculations performed in the model space π(0f_5/2,1p_3/2,1p_1/2,0g_9/2)ν(1p_1/2,0g_9/2) well reproduce experimental excitation energies and transition strengths in ⁸⁷Y, especially the large B(M1) values of up to 1.8 W.u. between yrast states with J>21/2. Structural differences between ⁸⁷Y and the isotone ⁸⁵Rb are discussed on the basis of the shell-model calculations.