Structure ofNe18

Abstract

We have studied $^{18}\mathrm{Ne}$ states up to 9 MeV excitation energy via the $^{16}\mathrm{O}$($^{3}\mathrm{He}$,$n$)$^{18}\mathrm{Ne}$ and $^{20}\mathrm{Ne}$($p$,$t$)$^{18}\mathrm{Ne}$ reactions. Excitation energies, widths, absolute cross sections, and angular distributions were measured. Distorted-wave Born approximation calculations were performed for comparison with the ($^{3}\mathrm{He}$,$n$) angular distributions and the ($p$,$t$) data were compared with previous calculations. Members of the 4.5-MeV doublet were found to have excitation energies of 4.518 \ifmmode\pm\else\textpm\fi{} 0.008 and 4.590 \ifmmode\pm\else\textpm\fi{} 0.008 MeV with spin and parity ${1}^{\ensuremath{-}}$ and ${0}^{+}$, respectively. The 5.1-MeV group was resolved into a doublet with 5.090 \ifmmode\pm\else\textpm\fi{} 0.008 and 5.144 \ifmmode\pm\else\textpm\fi{} 0.008 MeV excitation energies. Several previously unidentified states were found at excitation energies greater than 5 MeV, including a state at 7.062 \ifmmode\pm\else\textpm\fi{} 0.012 MeV that is strongly populated via ($^{3}\mathrm{He}$,$n$), but not observed in ($p$,$t$). We calculated two-particle Coulomb energy shifts for model mass-18 $T=1$ states and found that the difference between the excitation energy of the 4.59-MeV ${0}^{+}$ state and the analogous state at 5.34 MeV in $^{18}0$ gives strong evidence for the predominantly ${{s}_{\frac{1}{2}}}^{2}$ character of the state.NUCLEAR REACTIONS, NUCLEAR STRUCTURE $^{16}\mathrm{O}$($^{3}\mathrm{He}$,$n$)$^{18}\mathrm{Ne}$, $E=10\ensuremath{-}22$ MeV; measured $\ensuremath{\sigma}({E}_{n},\ensuremath{\theta})$. $^{20}\mathrm{Ne}$($p$,$t$)$^{18}\mathrm{Ne}$, $E=41.8$ MeV; measured $\ensuremath{\sigma}({E}_{t},\ensuremath{\theta})$. Gas targets. DWBA analysis. Deduced $^{18}\mathrm{Ne}$ levels, J, $\ensuremath{\pi}$. Calculated Coulomb shifts for model mass 18 $T=1$ states.