  We present the initial results of a study aimed at computing the global
effects of the X-ray ionization due to young stars within a molecular cloud
that forms stars with a standard IMF at a rate accelerating with time. We model
the gas distribution of the cloud as a fractal of dimension 2.3. We introduce
the concept of a "Roentgen sphere" as the region around each PMS star where the
ionization rate due to stellar X-rays exceeds that due to interstellar cosmic
rays. Using values of the X-ray luminosity typical of T Tauri stars, we find
that within the Roentgen radius the average ionization rate is increased by a
factor 4 to 20 with respect to the value obtained from cosmic-rays.
