Scattering of 40-Mev Protons fromHe4

The existence of an excited state in ${\mathrm{He}}^4$ may be investigated by bombarding these nuclei with a mono-energetic beam of protons and looking for a group of inelastically scattered protons corresponding to excitation of the state. Using this technique at a bombarding energy of 32-Mev, Benveniste and Cork found no evidence of a state in ${\mathrm{He}}^4$ of excitation energy less than 23 Mev. The 40-Mev beam of the Minnesota proton linear accelerator has been used to extend the search for a state in ${\mathrm{He}}^4$ to higher excitation energies. A gas target was bombarded and particles emitted at forward angles were detected in a scintillation counter which measured their energy. By observing the energy loss in traversing thin foils, the masses of the emitted particles were determined. Elastically scattered protons and recoil ${\mathrm{He}}^4$ were seen, as well as deuterons and recoil ${\mathrm{He}}^3$ from the ground state ($p, d$) reaction. A continuum of protons from ($p, 2p$) and ($p, \mathrm{pn}$) reactions was observed. No evidence was found for a group of inelastically scattered protons corresponding to excitation of a state in ${\mathrm{He}}^4$ of energy less than 28 Mev.