Angular distributions of alpha particles from the ${\mathrm{O}}^{16}(p, \alpha ){\mathrm{N}}^{13}$ ground-state reaction were measured with an ionization chamber at 10 bombarding energies from 13.5 to 18.1 Mev. The angular distributions are oscillatory but not of the form predicted by the plane wave pickup or knockon theories, and the variation with energy is more pronounced than would be expected for a simple direct reaction. The excitation curve has a minimum at $E_p\simeq 16.5$ Mev, and the angular distributions are markedly different above and below that energy. The ${\mathrm{O}}^{16}(p, \alpha ){\mathrm{N}}^{13*}$(2.4 Mev) reaction is also strongly energy dependent, and the ${\mathrm{O}}^{16}(p, p){\mathrm{O}}^{16}$ elastic scattering cross section is quite energy sensitive at large angles. The energy dependence of the scattering cross section at 125° appears to be correlated with the ${\mathrm{O}}^{16}(p, \alpha ){\mathrm{N}}^{13}$ excitation function.

• Received 10 April 1961

DOI:https://doi.org/10.1103/PhysRev.123.1304