# First observation of 20B and 21B

## TL;DR

This paper reports the first observation of the neutron-rich isotopes 20B and 21B, identifying their resonant states and decay modes, and confirming their masses align with recent atomic-mass extrapolations.

## Contribution

First experimental observation of 20B and 21B isotopes, including their resonance states and decay channels, expanding knowledge of neutron-rich boron isotopes.

## Key findings

- Observed 20B and 21B as resonances.
- Identified decay channels involving neutrons.
- Masses agree with atomic-mass extrapolations.

## Abstract

The most neutron-rich boron isotopes 20B and 21B have been observed for the first time following proton removal from 22N and 22C at energies around 230 MeV/nucleon. Both nuclei were found to exist as resonances which were detected through their decay into 19B and one or two neutrons. Two-proton removal from 22N populated a prominent resonance-like structure in 20B at around 2.5 MeV above the one-neutron decay threshold, which is interpreted as arising from the closely spaced 1-,2- ground-state doublet predicted by the shell model. In the case of proton removal from 22C, the 19B plus one- and two-neutron channels were consistent with the population of a resonance in 21B 2.47+-0.19 MeV above the two-neutron decay threshold, which is found to exhibit direct two-neutron decay. The ground-state mass excesses determined for 20,21B are found to be in agreement with mass surface extrapolations derived within the latest atomic-mass evaluations.