Low-Spin Levels In Sm-140: Five 0(+) States And The Question Of Softness Against Nonaxial Deformation

Background: Investigation of the Sm-140(62)78 nucleus, situated in the area close to the magic N = 82 neutron shell, offers the opportunity to find and study interesting phenomena resulting from the interplay of collective and other degrees of freedom.Purpose: Experimental identification of low-spin low-energy levels, particularly 0(+), in Sm-140 and theoretical interpretation within the collective general Bohr Hamiltonian (GBH) model.Method: The gamma-gamma angular correlation technique for. radiation after the beta/EC decay of Eu-140 -> Sm-140 and Gd-140 -> Eu-140 -> Sm-140 was used to determine spins of excited states of Sm-140. The Gd-140 and Eu-140 nuclei were produced in the Pd-104+Ar-40 reaction at the HIL UW cyclotron. In the theoretical part the full five-dimensional GBH model was applied in two variants: the simple phenomenological Warsaw model and the microscopic version with six inertial functions and a potential calculated from mean-field theory.Results: The spin and parity of six low spin (0,1,2) low lying excited levels of Sm-140 were measured. Two new states at around 2 MeV were identified. A analysis of the consequences of possible admixtures on the determination of the spin of a level was performed. The theoretical models applied successfully describe most of the spectrum of Sm-140 giving hints on the origin of the states observed in the experiment.Conclusions: Significant softness against nonaxial deformation seems to be essential to interpret the properties of Sm-140. Further experimental studies are needed to check if some low-energy excitations are not deformation driven.