Basic aspects of photon transport through matter with respect to track structure formation

After a short summary of the most important physical aspects of photon interaction with matter and of the main elements of photon transport simulation, some basic features of photon tracks in liquid water are discussed. These include the statistical distribution of the number of photon interactions caused during the complete photon slow-down, the corresponding mean value, the distance distribution of photon interactions, and the spectral distribution of secondary electrons or, which is the same, the spectral distribution of the start energy of secondary electron tracks. The latter distribution can easily be interpreted in terms of the track entity concept of Mozumder and Magee, which, therefore, proves to be the most natural concept of track structure analysis in the case of photon irradiation.