The $^{8}$He and $^{10}$He spectra studied in the $(t$,$p)$ reaction

TL;DR

This study investigates the low-lying energy spectra of helium-8 and helium-10 nuclei using transfer reactions, revealing specific excited states, a potential new ground state for helium-10, and discussing near-threshold anomalies.

Contribution

The paper provides new experimental data on helium isotopes' spectra and suggests a revised ground state energy for helium-10, enhancing understanding of their nuclear structure.

Findings

Identification of excited states in $^8$He at 3.6-3.9 MeV and 5.3-5.5 MeV.

Evidence for a state at about 7.5 MeV in $^8$He.

Observation of a possible ground state in $^{10}$He at about 3 MeV.

Abstract

The low-lying spectra of $^8$He and $^{10}$He nuclei were studied in the $^3$H($^6$He,$p$)$^8$He and $^3$H($^8$He,$p$)$^{10}$He transfer reactions. The $0^+$ ground state (g.s.) of $^8$He and excited states, $2^+$ at $3.6-3.9$ MeV and $(1^+)$ at $5.3-5.5$ MeV, were populated with cross sections of 200, 100-250, and 90-125 $\mu$b/sr, respectively. Some evidence for $^8$He state at about 7.5 MeV is obtained. We discuss a possible nature of the near-threshold anomaly above 2.14 MeV in $^8$He and relate it to the population of a $1^-$ continuum (soft dipole excitation) with peak value at about 3 MeV. The lowest energy group of events in the $^{10}$He spectrum was observed at $\sim 3$ MeV with a cross section of $\sim 140$ $\mu$b/sr. We argue that this result is possibly consistent with the previously reported observation of $^{10}$He, in that case providing a new g.s. position for $^{10}$He at about 3 MeV.