Monte Carlo calculation of CRT screen efficiency

The influence of phosphor grain size on overall CRT screen efficiency has been studied by Monte Carlo calculation of the energy absorption and the photon propagation in the phosphor screen. To calculate the energy absorption, the phosphor layer is modeled as a randomly packed layer of spheres with defined size distribution and screen weight. The absorbed energy in the phosphor grains is obtained from cross sections of the physical processes involved. The optical efficiency is calculated taking into account the scattering and absorption probability of the photons within the phosphor screen. The optimal screen efficiency which can be obtained for CRT screens with constant phosphor powder efficacy and aluminum reflectivity increases with increasing median grain size of the phosphor powder. Depending on the actual anode voltage applied, the CRT screen efficiency increases for a 32-kV anode voltage by 15%, going from 3- to 8-μm median grain size of the phosphor powder. Larger grains at this anode voltage do not further increase the efficiency. Grain-size distribution has no noticeable influence on screen efficiency.