WNPPC2025 - 62nd Winter Nuclear & Particle Physics Conference

β-decay of 68Mn: Probing the N=40 island of inversion

14 Feb 2025, 09:15

15m

Kinnear Centre Room (KC 303) (Banff, Alberta)

Contributed Oral Nuclear Structure Morning 1 - Nuclear Physics

Speaker

Rashmi Umashankar (TRIUMF)

Description

Although the shell model forms the backbone of our understanding of nuclear structure, the breakdown of traditional magic numbers far from stability gives insight into the nature of the underlying nuclear interactions and acts as a tool to test existing models. Islands of inversion (IoI) in the nuclear landscape are characterized by the presence of deformed multi-particle multi-hole (npnh) ground states instead of the (0p0h) configurations predicted by spherical mean-field calculations. In the N=40 region, the relatively large energy gap separating the pf shell from the neutron g${}_{9/2}$ orbital points towards a strong sub-shell closure at N=40 which has been supported by the observation of a high-lying 2+ state and low B(E2) value in ${}^{68}$Ni (Z=28). However, systematics of E(2+) and B(E2) values have indicated a sudden increase in collectivity below Z=28 when approaching N=40, seen especially in the rapid drop of E(2+) in Fe(Z=26) and Cr(Z=24) isotopes. This increase in collectivity around N=40 and Z<28 is thought to be due to the neutron occupation of intruder states from a higher shell, similar to the IoI around N=20. Recent studies also suggest the occurrence of a new IoI at N=50 and a proposed merging of the N=40 and N=50 IoIs, equivalent to the one observed between N=20 and N=28. Detailed spectroscopic information of the Fe, Co, and Ni isotopes will be crucial to understand the structure of nuclei near and inside the N=40 IoI and map the bridge between N=40 and N=50. To this end, an experiment was performed at TRIUMF using the GRIFFIN spectrometer that utilized the β and βn decay of ${}^{68}$Mn to populate excited states in ${}^{67,68}$Fe, Co and Ni. The dataset thus obtained features higher statistics than any previous β-decay study of these isotopes. Preliminary results from this analysis which include expanded level schemes, a re-measurement of the P${}_n$ value and tentative spin assignments from angular correlation analysis will be presented and discussed.

Presentation materials

68Mn-Rashmi-WNPPC.pptx