Orbital magnetic dipole strength in 148,150,152,154Sm and nuclear deformation.

Abstract

Nuclear-resonance-fluorescence spectra have been measured in the chain of $^{148,150,152,154}\mathrm{Sm}$ isotopes. Together with supplementary information from inelastic electron scattering and other reaction studies, orbital M1 transition strengths have been deduced for a number of ${1}^{+}$ states located around an excitation energy of 3 MeV. The systematic study, carried out for the first time, for nuclei within a large range of the deformation parameter \ensuremath{\delta} shows that the orbital M1 strength varies quadratically with \ensuremath{\delta}. This result is interpreted in terms of models containing explicitly neutron and proton degrees of freedom.