${\mathrm{He}}^3$-induced reactions in carbon have been studied for bombarding energies in the range 1.0 to 3.0 Mev. Absolute excitation curves have been obtained for the proton groups leading to the first three states in ${\mathrm{N}}^{14}$ and for the neutron group leading to the ${\mathrm{O}}^{14}$ ground state; these show pronounced resonance structure corresponding to levels in ${\mathrm{O}}^{15}$. Angular distributions have been measured at seven different energies for protons and four for neutrons. These distributions are not directly explicable as resulting from either compound nucleus or direct interaction processes but do show marked structure. The threshold for the ${\mathrm{C}}^{12}({\mathrm{He}}^3, n){\mathrm{O}}^{14}$ reaction has been determined to be 1449.6±2.8 kev, which requires a mass defect for ${\mathrm{O}}^{14}$ of 12.146±0.0065 Mev. The total cross sections for the (${\mathrm{He}}^3$, $n$) reaction to the ${\mathrm{O}}^{14}$ ground state and for the (${\mathrm{He}}^3$, $p$) reaction to the analog 2.3-Mev state in ${\mathrm{N}}^{14}$ are in the ratio 2:1, and the angular distributions for protons and neutrons from these reactions are quite similar at energies somewhat above the neutron threshold, as would be expected. The total cross sections for the (${\mathrm{He}}^3$, $p$) reaction range from 0.03 to 25 mb at these energies. The cross section of the ${\mathrm{C}}^{12}({\mathrm{He}}^3, {\alpha }_0){\mathrm{C}}^{11}$ reaction has been found to be approximately an order of magnitude greater than that of the ${\mathrm{C}}^{12}({\mathrm{He}}^3, n_0){\mathrm{O}}^{14}$ reaction and is suggestive of direct interaction.

• Received 29 October 1956

DOI:https://doi.org/10.1103/PhysRev.105.957