Abstract
Prompt -ray spectroscopy of the neutron-rich , produced in transfer- and fusion-induced fission reactions, has been performed using the combination of the Advanced Gamma Tracking Array and the spectrometer. A second excited state, assigned to , is observed for the first time, and a previously reported level energy of the first excited state is confirmed. The measured energy ratio indicates that this nucleus does not show a well-developed collectivity contrary to that seen in heavier isotones. This new measurement highlights an abrupt transition of the degree of collectivity as a function of the proton number at , of similar amplitude to that observed at at higher values. A possible reason for this abrupt transition could be related to the insufficient proton excitations in the , , and orbitals to generate strong quadrupole correlations or to the coexistence of competing different shapes. An unexpected continuous decrease of as a function of the neutron number up to is also evidenced. This measurement establishes the Kr isotopic chain as the low- boundary of the island of deformation for isotones. A comparison with available theoretical predictions using different beyond mean-field approaches shows that these models fail to reproduce the abrupt transitions at and .
- Received 27 January 2017
DOI:https://doi.org/10.1103/PhysRevLett.118.162501
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society