Low-spin levels in Sm140 : Five 0+ states and the question of softness against nonaxial deformation

Abstract

Background: Investigation of the 140 62 Sm 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 140 Sm and theoretical interpretation within the collective general Bohr Hamiltonian (GBH) model. Method: The γ -γ angular correlation technique for γ radiation after the β/EC decay of 140 Eu → 140 Sm and 140 Gd → 140 Eu → 140 Sm was used to determine spins of excited states of 140 Sm. The 140 Gd and 140 Eu nuclei were produced in the 104 Pd + 40 Ar 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 140 Sm 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 140 Sm 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 140 Sm. Further experimental studies are needed to check if some low-energy excitations are not deformation driven.

Prevailing Triaxial Shapes in Heavy Nuclei Driven by πMeson

“…The K quantum number is approximately conserved in the present case as the actual γ value is well below 15 • . This is well known feature, for instance [41], and is discussed for 166 Er in Ref. [42].…”