Exploring the "Island of Inversion" by in-beam gamma-ray spectroscopy of the neutron-rich sodium isotopes 31,32,33Na

TL;DR

This study used in-beam gamma-ray spectroscopy to explore the structure of neutron-rich sodium isotopes 31,32,33Na, revealing new excited states and supporting the existence of a rotational band within the Island of Inversion.

Contribution

It reports the first observation of excited states in 32,33Na and identifies a new decay gamma-ray in 31Na, advancing understanding of nuclear structure in this region.

Findings

New decay gamma-ray observed in 31Na

Excited states reported for 32Na and 33Na for the first time

Evidence supports a rotational band from a 2p2h intruder configuration

Abstract

The structure of the neutron rich sodium isotopes 31,32,33Na was investigated by means of in-beam gammaray spectroscopy following one-neutron knockout and inelastic scattering of radioactive beams provided by the RIKEN Radioactive Ion Beam Factory. The secondary beams were selected and separated by the fragment separator BigRIPS and incident at ~240 meV/u on a natural carbon (secondary) target, which was surrounded by the DALI2 array to detect coincident de-excitation gammarays. Scattered particles were identified by the spectrometer ZeroDegree. In 31Na, a new decay gammaray was observed in coincidence with the known (5/2+)-> 3/2(+) transition, while for 32,33Na excited states are reported for the first time. From a comparison to state-of-the-art shell model calculations it is concluded that the newly observed excited state in 31Na belongs to a rotational band formed by a 2p2h intruder configuration within the "Island of Inversion".