Abstract
Background: In the “island of inversion,” ground states of neutron-rich -shell nuclei exhibit strong admixtures of intruder configurations from the shell. The nucleus , located at the boundary of the island of inversion, serves as a cornerstone to track the structural evolution as one approaches this region.
Purpose: Spin-parity assignments for excited states in , especially negative-parity levels, have yet to be established. In the present work, the nuclear structure of was investigated by in-beam -ray spectroscopy mainly focusing on firm spin-parity determinations.
Method: High-intensity rare-isotope beams of , , , and bombarded a Be target to induce nucleon removal reactions populating states in . rays were detected by the state-of-the-art -ray tracking array GRETINA. For the direct one-neutron removal reaction, final-state exclusive cross sections and parallel momentum distributions were deduced. Multinucleon removal reactions from different projectiles were exploited to gain complementary information.
Results: With the aid of the parallel momentum distributions, an updated level scheme with revised spin-parity assignments was constructed. Spectroscopic factors associated with each state were also deduced.
Conclusions: Results were confronted with large-scale shell-model calculations using two different effective interactions, showing excellent agreement with the present level scheme. However, a marked difference in the spectroscopic factors indicates that the full delineation of the transition into the island of inversion remains a challenge for theoretical models.
3 More- Received 25 June 2020
- Accepted 9 October 2020
DOI:https://doi.org/10.1103/PhysRevC.102.054318
©2020 American Physical Society