Zakopane 2026 Conference on Nuclear Physics

The neutron-rich rare-earth nuclei form a pronounced region of the nuclear chart associated with prolate deformation. The shape evolution of these open-shell nuclei are intrinsically dependent on the neutron/proton number and consequently the underlying single-particle structure [1], and its interplay with collective phenomena such as deformation. K-isomerism, in combination with $\gamma$ ray spectroscopy, serves as a powerful tool to probe the nature of single-particle structures and the low-lying excitation energy spectrum below the isomer. An experiment was conducted at the GSI Helmholtzzentrum für Schwerionenforschung GmbH in Darmstadt, Germany, at the final focal plane of the GSI FRagment Separator, with the Decay Spectroscopy setup [2]. A primary beam of $^{170}$Er was fragmented to produce nuclei in the ranges $62 \leq Z \leq 67$ and $94 \leq N \leq 102$. Our recent spectroscopic results are the identification of a new isomeric state of $^{157}$Sm and $^{164}$Tb. The measured observables provide insight into the developing single-particle structures and shedding new light on the evolution of deformation in this mass region.

[1] Yusuke Tsunoda, Takaharu Otsuka, Noritaka Shimizu, Michio Honma, and Yutaka Utsuno. Physical Review C, 89(3):031301, 2014.
[2] A. K. Mistry et al. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1033:166662, 2022.