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The $\nu11/2^{-}[505]$ orbital that extends from below the $N = 82$ shell-closure, dubbed the ``flying fish'', has been described as pivotal in contributing to the deformation in the neutron-rich rare-earth nuclei [1]. The flying fish leaps up towards the Fermi surface with increasing deformation and neutron number and then flops back into the Fermi sea as the neutron number further increases. The sudden onset of deformation in the mass $A \sim 150$ region has been attributed to the interplay between the spherical-driving extruder ($\textit{h}_{11/2}$) orbital and deformation-driving intruder orbital(s) ($\textit{i}_{13/2}$), this provides a natural scenario for shape coexistence phenomena [2].
A beam of $^{170}$Er was fragmented at $1.08 \, \mathrm{GeV/u}$ on a $6 \, \mathrm{g/cm}^{2}$ $^{9}$Be target for the first time at GSI in the spring of 2024 as part of the FAIR Phase-0 experimental campaign. The fragmentation products from the target were separated and identified with the GSI Fragment Separator and transported to the final detection focal plane, which were stopped in the DEPSEC hybrid decay spectroscopy setup [3]. The DESPEC hybrid setup allows the simultaneous spectroscopy of level structure information from a suite of 12 high-purity germanium triple-cluster detectors (DEGAS) and lifetime measurements from 36 LaBr$_{3}$ (FATIMA) detectors.
Our new results on the spectroscopy of $^{157}$Sm and $^{159}$Sm provide us an insight into evolving single-particle structures and their interaction with collective phenomena along the odd$-N$ Sm ($Z = 62$) isotopic chain. These results indicate a vanishing role of the $\nu11/2^{-}[505]$ in the low-lying level structure between $^{157}$Sm and $^{159}$Sm, as similarly observed at different neutron number in the isotopic chains of Gd, Dy and Er.
[1] J. F. Sharpey-Schafer et al., EPJ A 55, 15 (2019).
[2] P. Kleinheinz et al., PRL 32, 68 (1974).
[3] A. Mistry et al., NIM A 1033, 166662 (2022).