Photon-Induced Beta Decay in Stellar Interiors

Because of the astrophysical importance of beta-decay lifetimes in stellar interiors, we have calculated the rate of photon-induced beta decay ("photobeta" decay). In the photobeta process the photon can be considered to decay virtually into an electron-positron pair, with the positron being absorbed by the nucleus. The photobeta process is in competition with normal beta decay (if energetically possible), excited-state beta decay, and free-positron capture. An infrared divergence problem for exothermic photobeta decay is discussed, although the exothermic photobeta rate is too small to enhance most spontaneous beta decays. Applications are discussed in the driven decay of stable nuclei. As an example, the photobeta lifetime of a nucleus stable by 200 keV drops from 3\ifmmode\times\else\texttimes\fi{}${10}^{10}$yr at 3\ifmmode\times\else\texttimes\fi{}${10}^{8}$ \ifmmode^\circ\else\textdegree\fi{}K, to ${10}^{5}$yr at 1.2\ifmmode\times\else\texttimes\fi{}${10}^{9}$ \ifmmode^\circ\else\textdegree\fi{}K for a nuclear transition matrix element characterized by log ft=6. The competition between the photobeta process and excited-state beta decay is discussed.