Description of orbital and spin excitations within a projected spherical single-particle basis

Orbital and spin excitations in even Sm isotopes have been studied microscopically in a quasi-particle random phase approximation approach formulated in the laboratory frame using a projected spherical single-particle basis which reproduces the Nilsson level scheme to a good approximation. The orbital magnetic dipole excitations are found to fall below 4 MeV with a summed strength which follows closely the observed deformation quadratic law. The M1 spin strength is found to be strongly fragmented over a range of 4 to 10 MeV and, in the case of the well deformed 154Sm isotope, distributed so as to reproduce the double hump pattern observed experimentally. ((orig.))