Speaker
Description
The rare-earth region provides an ideal testing ground for nuclear structure evolution, where enhanced collectivity and low-lying 0+ states challenge simple models and require additional degrees of freedom such as triaxial and octupole deformation. Much of the existing experimental data, however, is concentrated in the stable Nd–Dy region, and it remains unclear whether these models can be extended to higher proton numbers.
Neutron-deficient erbium isotopes provide access to the N∼90 transitional region at higher proton numbers, where experimental data are scarce and theoretical descriptions remain largely untested. In this region, while the ground-state band evolves smoothly toward the N=82 shell closure, the excited 0+ band exhibits a minimum in energy at N=90, indicating a change in structure and possible mixing of different configurations across 156,158,160Er.
A Coulomb-excitation experiment has been performed at TRIUMF using a radioactive 158Er beam with γ rays detected by TIGRESS. Combined with complementary new data from β-decay, the analysis aims to extract precise E2 matrix elements between the ground state band and the K = 0,2 bands of 158Er, to distinguish between collective and quasiparticle excitations, constrain band structure and possible triaxiality, and determine model-independent shape parameters using Kumar–Cline sum rules. GOSIA analysis is in progress, and preliminary results provide insight into the structure and collectivity of 158Er.