How is the speed of an intensifying screen defined?

• A. The phosphor crystal size determines the speed
• B. The intensification factor, calculated as exposure without screens divided by exposure with screens
• C. The film thickness determines the speed
• D. The processing time of the film determines the speed

Answer: (B)

Speed describes how much the screen lowers the exposure needed to reach a given film density. It is defined by the intensification factor, which is the exposure required without the screen divided by the exposure required with the screen. A larger factor means the screen provides more amplification, so you can use much less radiation to achieve the same image density. For example, if you’d need 1000 units of exposure without the screen and 100 units with the screen, the intensification factor is 10, meaning the screen is ten times faster. Phosphor crystal size and layer thickness influence the actual speed in practice, but the definitional measure is this ratio. Film thickness and processing time do not set the screen’s speed.