The Cross Section for the Radiative Capture of Protons by<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">C</mml:mi></mml:mrow><mml:mrow><mml:mn>12</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>near 100 Kev

A low voltage accelerator and high current ion source has been used to determine the cross section of the reaction ${\mathrm{C}}^{12}(p\ensuremath{\gamma}){\mathrm{N}}^{13}$ 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 ${\mathrm{N}}^{13}$ 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 ${10}^{\ensuremath{-}16}$ positron per proton and cross sections as low as ${10}^{\ensuremath{-}10}$ barn or ${10}^{\ensuremath{-}34}$ ${\mathrm{cm}}^{2}$ can be measured with errors of the order of \ifmmode\pm\else\textpm\fi{}20 percent. The cross section for the ${\mathrm{C}}^{12}(p\ensuremath{\gamma}){\mathrm{N}}^{13}$ reaction has been found to fit the semi-empirical expression $\ensuremath{\sigma}=0.0024{E}^{\ensuremath{-}1}\mathrm{exp}[\ensuremath{-}6{E}^{\ensuremath{-}\frac{1}{2}}]$ 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.

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