  A new method for the inclusion of ionizing radiation from uniform radiation
fields into 3D Smoothed Particle Hydrodynamics (SPHI) simulations is presented.
We calculate the optical depth for the Lyman continuum radiation from the
source towards the SPHI particles by ray-tracing integration. The
time-dependent ionization rate equation is then solved locally for the
particles within the ionizing radiation field. Using test calculations, we
explore the numerical behaviour of the code with respect to the implementation
of the time-dependent ionization rate equation. We also test the coupling of
the heating caused by the ionization to the hydrodynamical part of the SPHI
code.
