Quantum Utilization in X-Ray Intensifying Screens

It is the purpose of this paper to present a comprehensive comparison of the different rare-earth oxysulfide x-ray screens. Relative speed and resolution of Y2O2S:Tb, La2 O2S:Tb and Gd2O2S:Tb as used with conventional x-ray film and experimental (green sensitive) x-ray film are reported. A comparison is also made of the performance of the experimental rare-earth oxysulfide screens and commercial CaWO4 screens. Both La2O2S:Tb and Gd2O2S:Tb are observed to be considerably faster than Y2O2S:Tb and CaWO4 for screens of comparable resolution. La2O2S:Tb perform better for tube voltage below 90 kVp. Above 90 kVp, Gd2 O2S:Tb is best. These performance characteristics are related to the quantum utilization of the screens. The quantum utilization is defined as the fraction of the x-ray energy incident upon the screen that is actually absorbed by the screen. Calculations of the quantum utilization for oxysulfide and CaWO4 screens are presented.