Abstract
The absolute efficiency of X-ray phosphor screens was studied in reflection mode observation for two phosphor materials widely used in X-ray applications, namely Y2O2S:Tb and Gd2O2S:Tb. The efficiency proved to depend on the tube voltage and on the screen thickness. Comparisons are given between the efficiency of the same screens in reflection and transmission mode observation. Theoretical calculations based on a uniform screen model give results that are in very good agreement with the experimental data.