The process of generating a Cerenkov photon is called CKOV and corresponds to the process value 105 (variable LMEC in common /GCTRAK/). This process is activated only in a radiator defined via the routine GSCKOV.
The process of photon absorption (name LABS, code 101) is controlled by the LABS FFREAD data record. By default the process is activated for all the materials for which optical properties have been defined.
The action taken at the boundary is identified by the process name LREF, code 102.
At a boundary a photon can be either reflected (name REFL, code 106) or refracted (name REFR, code 107).
M.Hansroul, G.R.Lynch