A search has been made for excited states in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ by investigating proton-induced reactions on ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$. The investigation consisted of two parts. In the first part, a kinematically incomplete experiment, the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and $\alpha$-particle continua from the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}(p,{}_{}{}^3{}_{}{}^{}\mathrm{He})$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}(p,\alpha )$ reactions at an incident proton energy of 45.0 MeV have been studied for structure due to excited states in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, respectively. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and $\alpha$-particle spectra were measured from 15 to 90° (lab) in steps of 5° using a $\Delta E-E$ detector telescope. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ spectra exhibit clearly discernible peaks due to the 20.2-MeV ($0^{+}$, $T=0\mathrm{}$) and 21.4-MeV ($0^{-}$, $T=0\mathrm{}$) excited states in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. In the $\alpha$-particle spectra no structure has been observed that could be interpreted as due to excited states in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ for excitation energies up to 17.5 MeV. An upper limit of 30 μb/sr could be set for the excitation of states in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ having a width $\lesssim 1.0$ MeV. In the second part, a kinematically complete experiment, a study has been made of the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}(p,\alpha d)p$ reaction at an incident proton energy of 45.0 MeV. This investigation was carried out to study final-state interactions and, in particular, to search for a possible $p-d$ final-state interaction corresponding to a resonance in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. Coincidence spectra from the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}(p,\alpha d)p$ reaction were measured in coplanar geometry with the $\alpha$-particle detector set at 50° (lab), while the deuteron-detector telescope was moved in steps of 10° from -100 to -50° (lab), and with the $\alpha$-particle detector set at 30° (lab) and the deuteron-detector telescope at -100 and -80° (lab). The measured coincidence spectra show a prominent $p-\alpha$ final-state interaction corresponding to the ground state of ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$. No other strong $p-\alpha$ final-state interaction was observed. The coincidence spectra do not exhibit a $p-d$ final-state interaction corresponding to a $T=\frac{1}{2}$ resonance in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ of excitation between 5.5 and 20 MeV.

• Received 30 November 1970

DOI:https://doi.org/10.1103/PhysRevC.3.1771