Structure of high-spin states in ⁸⁹Sr and ⁹⁰Sr

High-spin states of ⁸⁹Sr and ⁹⁰Sr were studied via the reactions ⁸²Se(¹¹B,p4n) and ⁸²Se(¹¹B ,p3n), respectively, at a beam energy of 37 MeV. Gamma rays were detected with the GASP spectrometer. The level schemes of ⁸⁹Sr and ⁹⁰Sr were extended up to E ≈ 8 MeV and E ≈ 10 MeV, respectively. The level structures in ⁸⁹Sr and ⁹⁰Sr were interpreted in terms of the spherical shell model. The calculations were performed in the configuration space (0f_5/2, 1p_3/2, 1p_1/2, 0g_9/2) f or the protons and (1p_1/2, 0g_9/2, 1d_5/2) for the neutrons. High-spin level sequences in ⁸⁹Sr are characterized by coupling the unpaired d_5/2 neutron to proton excitations of the core nucleus ⁸⁸Sr. An equidistant level sequence with ΔJ = 2 found in ⁹⁰Sr is well described by the configuration π[(0f_5/2^-2) (0g_9/2²)] ν(1d_5/2²) which favors even spins.