Spectroscopy of neutron-unbound $^{27,28}$F

TL;DR

This paper reports the first observation of the unbound ground state of $^{28}$F and an excited state of $^{27}$F, providing insights into their shell structure and confirming theoretical predictions about their configurations.

Contribution

It presents the first experimental observation of the unbound states of $^{28}$F and $^{27}$F, advancing understanding of neutron-rich fluorine isotopes.

Findings

$^{28}$F ground state is 220 keV above $^{27}$F ground state.

First observation of neutron-unbound excited state in $^{27}$F at 2500 keV.

Results support $sd$-shell configuration dominance in $^{28}$F.

Abstract

The ground state of $^{28}$F has been observed as an unbound resonance $2\underline{2}0$ keV above the ground state of $^{27}$F. Comparison of this result with USDA/USDB shell model predictions leads to the conclusion that the $^{28}$F ground state is primarily dominated by $sd$-shell configurations. Here we present a detailed report on the experiment in which the ground state resonance of $^{28}$F was first observed. Additionally, we report the first observation of a neutron-unbound excited state in $^{27}$F at an excitation energy of $25\underline{0}0 (2\underline{2}0)$ keV.