Search for Excited States ofHe6

Abstract

The excitation spectrum of ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ has been examined through measurements of charged-particle energy spectra from four nuclear reactions. Triton energies up to 22 MeV were used to induce the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(t,\alpha ){}_{}{}^6{}_{}{}^{}\mathrm{He}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}\mathrm{}(t,p)\mathrm{}{}_{}{}^6{}_{}{}^{}\mathrm{He}$, and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}(t,{}_{}{}^3{}_{}{}^{}\mathrm{He}){}_{}{}^6{}_{}{}^{}\mathrm{He}$ reactions. Deuterons of 16- and 22-MeV energy were used to induce the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(d,{}_{}{}^3{}_{}{}^{}\mathrm{He}){}_{}{}^6{}_{}{}^{}\mathrm{He}$ reaction. All of the energy spectra show peaks from the ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ ground and first excited (1.80-MeV) states, but no other structure attributable to states of ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ was observed. Differential cross-section data for the ground and first excited states were obtained for three of the reactions. The ($d,{}_{}{}^3{}_{}{}^{}\mathrm{He}$) cross-section data were compared with the results of distorted-wave Born-approximation calculations and with data collected from the ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}(d,{}_{}{}^3{}_{}{}^{}\mathrm{He}){}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ reaction. These comparisons were consistent with an assignment of $2^{+}$ for the ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ 1.80-MeV state.