The cross section for the radiative capture of protons by C12 near 100 Kev

Abstract

A low voltage accelerator and high current ion source has been used to determine the cross section of the reaction C12(pγ)N13 over the energy range from 88 to 128 kev. A counter arrangement is described which detects 26 percent of all the positrons from the decay of the N13 produced in the reaction and which has a low background rate of 5.5 counts per minute. With this accelerator and detector, yields of the order of 10^-16 positron per proton and cross sections as low as 10^-10 barn or 10^-34 cm^2 can be measured with errors of the order of ±20 percent. The cross section for the C12(pγ)N13 reaction has been found to fit the semi-empirical expression σ=0.0024E^-1exp[-6E^-1/2] barn with E in Mev over the energy range measured. This is in satisfactory agreement with the Breit-Wigner one-level dispersion formula using constants determined at the 456-kev resonance. The astrophysical implications of these results in connection with the carbon-nitrogen cycle of nuclear reactions in stellar interiors are discussed.