Complete set of bound negative-parity states in the neutron-rich 18N nucleus

TL;DR

This study uses gamma-ray spectroscopy and shell-model calculations to identify all negative-parity states in neutron-rich 18N, providing new insights into nuclear structure and constraints for theoretical models relevant to astrophysical processes.

Contribution

The paper reports the first complete set of negative-parity states in 18N and constrains cross-shell interactions, advancing understanding of neutron-rich nuclei and nuclear models.

Findings

Six new negative-parity states identified

All expected negative-parity states below neutron threshold are accounted for

Strong constraints on cross-shell matrix elements provided

Abstract

High-resolution gamma-ray spectroscopy of 18N is performed with the Advanced GAmma Tracking Array AGATA, following deep-inelastic processes induced by an 18O beam on a 181Ta target. Six states are newly identified, which together with the three known excitations exhaust all negative-parity excited states expected in 18N below the neutron threshold. Spin and parities are proposed for all located states on the basis of decay branchings and comparison with large-scale shell-model calculations performed in the p-sd space, with the YSOX interaction. Of particular interest is the location of the 0^-_1 and 1^-_2 excitations, which provide strong constrains for cross-shell p-sd matrix elements based on realistic interactions, and help to simultaneously reproduce the ground and first-excited states in 16N and 18N, for the first time. Understanding the 18N structure may also have significant impact on neutron-capture cross-section calculations in r-process modeling including light neutron-rich nuclei.