Photoionization rate
= Photoionization rate
{title2=$\Gamma$}
For isotropic <specific intensity> $J_\nu$, absorption cross-section $\sigma_\nu$, and threshold frequency $\nu_0$, the photoionization rate per target atom is
$$
\Gamma=4\pi\int_{\nu_0}^\infty\frac{J_\nu\sigma_\nu}{h\nu}\,d\nu.
$$
For a directed incident flux, replace $4\pi J_\nu$ by its <spectral flux density>. The factor $h\nu$ converts energy flux into photon flux. This rate alone does not imply <photoionization equilibrium>.