MAGNETIC DIPOLE ELECTROEXCITATIONS IN RARE-EARTH NUCLEI

The M1 excitation of Kπ = 1+ states through inelastic electron scattering is studied in rare-earth nuclei within a quasiparticle RPA approach with quadrupole-quadrupole, spin-spin and spin-quadrupole residual interactions. The spurious state is removed exactly by a procedure which restores the rotational invariance of the RPA hamiltonian and leads to almost purely isovector vibrations. The DWBA (e, e') form factors and the strongly orbital low-energy M1 spectrum are in a good agreement with the rich experimental data. The purely collective scissor state has largest overlaps with the orbital low-energy RPA excitations but a single overlap does not exceed 15%. Nevertheless, a number of low-lying 1+ states, including the strongest experimentally observed M1 state, can be interpreted as isovector rotational vibrations due to their large overlaps with proposed phonon rotational states, in which only several quasiparticle pairs perform a scissor-type vibrational motion. © 1990.