- W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California, USA
Measurements of the elastic scattering of protons by C13 from 140 keV to 750 keV proton energy are reported. The radiative capture of protons by C13 has been investigated down to a proton energy of 130 keV, but no new levels are found that would influence the cross section at stellar energies. The only new level found has a resonance energy of 448.5±0.5 keV. An upper limit is placed on the strength of radiative capture by any missed levels. Angular distribution measurements, combined with the results of N14(?, ??) by other workers lead to an assignment J? = 2? for the 448-keV resonance (7.966 MeV excitation). From the same target used for the C13(p, ?) measurements, the yield of C12(p, ?) radiation has been measured, and the cross sections of both reactions are extrapolated to stellar energies. The extrapolated cross section factor S0 at 25 keV C.M. proton energy is 6.0±0.8 keV-barn for the C13(p, ?) reaction, and is 1.33±0.15 keV-barn for the C12(p, ?) reaction. The equibrium Ratio by number of C12 C13 in the CNO-cycle is thus 4.1±0.7 at a temperature of 15 × 106 °K.
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