Speaker
Description
The low excitation energies of the first excited $2^+$ states in the neutron-rich rare-earth nuclei are an indication of their degree of deformation [1]. Close to the double mid-shell, a subtle evolution seems to take place as the neutron number approaches $N = 104$ [2]. Additionally, recent progress in microscopic nuclear theory are providing alternative interpretations of the established view of these nuclei as prolate, axially symmetric rotors [3].
We performed the first ever projectile-fragmentation of $^{170}$Er with an energy of 1 GeV/u at the GSI Helmholtzzentrum für Schwerionenforschung GmbH in Darmstadt, Germany to expand the sparse nuclear structure information of the exotic neutron-rich rare-earth isotopes. The subsequent reaction products were cleanly separated and identified on an ion-by-ion basis using the GSI Fragment Separator before being implanted in the decay spectroscopy setup of the DESPEC collaboration [4]. Using the HPGe array DEGAS and LaBr$_3$ array FATIMA in combination allows for simultaneous high resolution spectroscopy and fast-timing measurements.
Our setup gives access to non-yrast isomeric states, providing new transitions, levels and lifetimes based on the $\gamma$ rays emitted after implantation of neutron-rich nuclei with $N\leq 102$ and $Z\leq67$. The unique production mechanism and exceptionally high yields allowed the discovery of new isomers as well as greatly expanding level schemes with levels not accessible with previous methods.
The isomeric decay of the $N = 102$ nucleus $^{168}$Dy was previously observed at RIKEN [5]. The significantly increased level of statistics in this work has allowed the observation of many new transitions, and required a reassessment of the previously deduced level scheme. The reinterpreted isomer with $K=6$ exhibits decays into several newly-observed structures indicating a complex wave function that overlaps with many different configurations.
This contribution focuses on the novel structures observed for $^{168}$Dy and other selected nuclei and how our results push the experimentally available nuclear structure information away from stability. We also theoretically describe our results using modern nuclear theory.
[1] A. Bohr and B. Mottelson, Nuclear structure volume 2: Nuclear deformations (World Scientific Publishing, New York,
1975).
[2] Z. Patel et al., PRL 113, 262502 (2014).
[3] T. Otsuka et al., EPJ A 61, 126 (2025).
[4] A. Mistry et al., NIM A 1033, 166662 (2022).
[5] G. Zhang et al., PLB 799, 135036 (2019).
| Contribution category | Experiment |
|---|---|
| Presenter status | Student |