The efficiency of absorption of x-ray photons in the scintillator plate is optimized to allow the best point spread function as well as good detector efficiency.

The absorption follows the equation:

form1.JPG

That means that at higher angles of incidence the efficiency of the detector is higher (provided that the standard efficiency is not 100 %) and has to be corrected. This efficiency can be verified by illuminating the detector with an x-ray source of a well defined spatial emission like x-ray fluorescence.   For the 40 mum thick Gd2O2S scintillator typical efficiency curves at various energies are depicted in the following graph:

stoppowerstopping power at a set of energies (45 kB)