Spectroscopy of narrow, high-lying, low-spin states inNe20

Abstract

The excited states of the $^{20}\mathrm{Ne}$ nucleus from the ground state to ${E}_{x}$ = 25 MeV were investigated with the $^{22}\mathrm{Ne}$($p,t$)$^{20}\mathrm{Ne}$ reaction at a beam energy of ${E}_{p}$ = 60 MeV using the QDD magnetic spectrometer at iThemba LABS. Narrow, low-spin ${J}^{\ensuremath{\pi}}={0}^{+},{1}^{\ensuremath{-}}$, and ${2}^{+}$ states have been observed for the first time at high-excitation energies in $^{20}\mathrm{Ne}$, namely at ${E}_{x}$ = 17.67, 18.84, 20.59, 21.16, 21.80, and 22.5 MeV. Shell-model and coupled reaction channel calculations were performed to determine the nature of the newly observed states. Candidates for $T$ = 2 states are proposed at 3.86(5), 4.43(5) MeV and 5.07(5) MeV above the lowest ${0}^{+},T$ = 2 state at ${E}_{x}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}16.73$ MeV. Two of these $T$ = 2 candidates appear to result from core excitations in the $0p$ shell. The state at ${E}_{x}$ = 22.5 MeV, which could not be interpreted by the shell-model calculations, is a tentative candidate for the 5-$\ensuremath{\alpha}$ cluster state.