Photobeta Reactions in Stellar Interiors.

Under equilibrium conditions in stellar interiors there is a small fractional population of the excited states of nuclei. Many of these excited states are unstable against the emission of positive and negative beta-particles and against the capture of free electrons. Expressions are given for the induced rates of these transformations. Applications are made to the process of heavy-element formation by neutron capture on a slow time scale which probably accompanies carbon thermonuclear reactions. From a consideration of the abundances of nuclei which are partially shielded against formation by neutron capture, it is shown that the terminal stages of the capture must have involved a temperature of about 7 X 108 K and a neutron flux of about 3 x 1717 neutrons/cm2 sec and that the flux must have been quickly terminated within a small fraction of 1 year of the time at which the heavy-element products were frozen. On the longer time scales characteristic of heavy-element formation in red giant stars, it is shown that Nb13 can be relatively quickly formed in the stellar interior and that the technetium isotope responsible for the presence of Tc lines in S spectra is probably Tc97 rather than Tc99.