The effect of phosphor K x-rays on the MFT of rare-earth screens

The LSF's and MTF's of two high resolution rare-earth screen-film combinations were measured at two beam qualities. The two beam qualities were chosen to provide x-ray spectral distributions either above or below the K-edge of the screen phosphor. The LSF's were found to be photon energy dependent. This energy dependence is attributed to the generation and reabsorption of phosphor K x-rays resulting in a broadening of the LSF.