# Towards the Limits of Existence of Nuclear Structure: Observation and First spectroscopy of the Isotope $^{31}$K by measuring its three-proton Decay

## TL;DR

This paper reports the first observation and spectroscopy of the extremely proton-rich isotope $^{31}$K, measuring its three-proton decay and determining its energy states and separation energy, thus exploring the limits of nuclear existence.

## Contribution

It provides the first experimental data on $^{31}$K, including its decay modes, energy states, and separation energy, extending knowledge of nuclear stability near the proton drip line.

## Key findings

- Observed $^{31}$K beyond the proton drip line.
- Measured three-proton decay and determined energy states.
- Established an upper half-life limit of 10 ps.

## Abstract

The most-remote from stability isotope $^{31}$K, which is located four atomic mass units beyond the proton drip line, has been observed. It is unbound in respect to three-proton (${3p}$) emission, and its decays have been detected in flight by measuring trajectories of all decay products using micro-strip detectors. The $3p$-emission processes have been studied by means of angular correlations $^{28}$S+3$p$ and the respective decay vertexes. The energies of the previously-unknown ground and excited states of $^{31}$K have been determined. This provides its $3p$ separation-energy value $S_{3p}$ of $-4.6(2)$ MeV. Upper half-life limits of 10 ps of the observed $^{31}$K states have been derived from distributions of the measured decay vertexes.