Energy absorbed in calcium tungstate x‐ray screens

The energy which must be absorbed in a CaWO 4 x‐ray intensifying screen to produce unit net optical density on a film has been evaluated by measurement and calculation for a screen–film system over a range of beam qualities (1.4–7.4 mm Al HVL) spanning the diagnostic x‐ray region. It was found to be constant within experimental error. The absorbed‐energy constant for three additional CaWO 4 screens is presented for a single beam quality. To correct the estimation of absorbed energy, the fractional escape of tungsten K x rays has been evaluated and the results are presented as a function of phosphor loading. The absorbed‐energy constant is useful for predicting optical density for variable beam conditions; a family of characteristic curves based on exposure is reduced to one curve for a particular film–screen system, expressed as optical density as a function of absorbed energy.