Fine structure of the giant M1 resonance in 90Zr

M1 excitations in the 90Zr nucleus have been studied in a photon-scattering experiment with monoenergetic and 100% linearly-polarized beams from 7 to 11 MeV. More than 40 Jπ = 1+ states were identified for the first time from the observed ground-state transitions revealing the fine structure of the giant M1 resonance with center of gravity of 9 MeV and sum strength of 3.8(3) μ2N. The results of the present work are compared with predictions from the shell model and the quasi-particle random-phase approximation.