Structure of A∼130 nuclei in La-Ce region

Abstract

The variety of shapes and structures, observed in light rare earth A ∼ 130 nuclei, have been discussed in view of different angular momentum coupling schemes and their interplay that comes into effect at high spin. The N = 79 and 80 isotopes in La-Ce region, produced via fusion evaporation reaction, have been studied using the Indian National Gamma Array (INGA) consisting of 18 clover HPGe detectors. Two nearly degenerate ΔI = 1 bands have been observed at high spin of 137Ce and a triaxial deformation of γ = ±30° has been assigned to the bands, from the total Routhian surface (TRS) calculations. The high-spin candidates of the yrast band of 138Ce show signature splitting both in energy and B(M1)/B(E2) values. The bandcrossing due to the alignment of a pair of h11/2 proton particles has been conjectured at ℏω ∼ 0.3 MeV, from the single-particle Routhians obtained from TRS calculations. Lifetime measurements by Doppler shift attenuation method (DSAM) has been carried out and from the estimated reduced transition probability B(M1), the ΔI = 1 band in 138Ce has been characterized as a magnetic rotation (MR) band. The rise in the values of B(M1), for the higher spin candidates of the band, has been conjectured as the reopening of a different shear at the top of the Band B1. The characteristic of the MR bands in A ∼ 130 region has been discussed in the light of a phenomenological calculation and compared to the MR bands in other mass regions.