High-spin structure of the spherical nucleus 90Y

High-spin states in 90Y were populated in the 82Se(11B,3n)
reaction at a beam energy of 37 MeV. Gamma rays were detected with the spectrometer GASP. The level scheme of 90Y was extended up to J^\pi = (18^+) at 9.6 MeV. Mean lifetimes of four levels were determined using the Doppler-shift-attenuation method. The structure of 90Y was
interpreted in terms of the shell model. The calculations were 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},1d_{5/2}) and in an extended space including the \nu(0g_{7/2})$ orbital as well. The calculations in the extended model space reveal a correspondence between states in ^{90}Y and ^{89}Y. Moreover, a combination of the predicted states with J^\pi \geq 14^(+) can be found
that reproduces the large B(M1) values of up to about 1 W.u.