The 90° yield of gamma rays from proton bombardment of ${\mathrm{C}}^{12}$ was studied for proton energies between 14 and 20 MeV. Gamma rays are observed corresponding to the ground-state decay of the ${\mathrm{C}}^{12}$ 4.43-, 12.7-, and 15.1-MeV levels and from the ${\mathrm{C}}^{12}(p, {\gamma }_0){\mathrm{N}}^{13}$ reaction. Three resonances are observed in the yield of the 15.1-MeV gamma ray. These resonances correspond to ${\mathrm{N}}^{13}$ levels at 18.1, 18.65, and 19.8 MeV. The ${\mathrm{N}}^{13}$ 18.1-MeV level has a width of 330±100 keV in the center-of-mass system. The other two levels have widths less than 200 keV. The yields of the 4.43- and 12.7-MeV gamma rays reveal little or no structure. The excitation function of the ${\mathrm{C}}^{12}(p, {\gamma }_0){\mathrm{N}}^{13}$ reaction also shows little structure. Angular distributions and absolute integrated cross sections for the ${\mathrm{C}}^{12}(p, p^{\prime }){\mathrm{C}}^{12}$ reaction are given for the ${\mathrm{C}}^{12}$ 12.7-MeV level with $E_p=17.5, 19.5, \mathrm{and} 20$ MeV and for the ${\mathrm{C}}^{12}$ 15.1-MeV level with $E_p=19.5\mathrm{}$ MeV. The latter is approximately symmetrical about 90° which suggests possible contribution from the compound nucleus reaction mechanism. Comparison of the cross sections for ${\mathrm{C}}^{12}(p, p^{\prime }\gamma ){\mathrm{C}}^{12}$ and ${\mathrm{C}}^{12}(p, p^{\prime }){\mathrm{C}}^{12}$ gives $\frac{{\Gamma }_{\gamma }}{\Gamma }=0.027\mathrm{}\pm 0.007$ for the ${\mathrm{C}}^{12}$ 12.7-MeV state and 1.15±0.3 for the ${\mathrm{C}}^{12}$ 15.1-MeV state. The yield of the ${\mathrm{C}}^{12}(p, d){\mathrm{C}}^{11}$ reaction was measured by the stacked foil technique from threshold ($E_p=17.85\mathrm{}$ MeV) to 19.8 MeV. There is no evidence for structure. Angular distributions are given for the ${\mathrm{C}}^{12}(p, d){\mathrm{C}}^{11}$ reaction for $E_p=19.3, 19.5, \mathrm{and} 20.0$ MeV. The results are compared to previous work on the ${\mathrm{B}}^{11}(d, n){\mathrm{C}}^{12}$ reaction and it is concluded that the contribution of the compound nucleus reaction mechanism to either reaction is most likely small for the bombarding energies in question.

• Received 2 July 1962

DOI:https://doi.org/10.1103/PhysRev.128.1810