Fine Structure Of The Giant M1 Resonance In Zr-90

The M1 excitations in the nuclide Zr-90 have been studied in a photon-scattering experiment with monoenergetic and linearly polarized beams from 7 to 11 MeV. More than 40 J(pi) = 1(+) states have been identified from observed ground-state transitions, revealing the fine structure of the giant M1 resonance with a centroid energy of 9 MeV and a sum strength of 4.17(56) mu(2)(N). The result for the total M1 strength and its fragmentation are discussed in the framework of the three-phonon quasiparticle-phonon model. DOI: 10.1103/PhysRevLett.110.022503