What is the light-sensitive material that coats radiographic film?

• A. Silver bromide crystals
• B. Calcium tungstate crystals
• C. Photographic gelatin
• D. Lead oxide crystals

Answer: (A)

The light-sensitive component of radiographic film is a layer of silver halide crystals dispersed in gelatin. In practice, silver bromide crystals are the primary light-sensitive material used. When X-rays expose the film, energy creates latent image centers within these silver halide crystals. During development, the exposed crystals are reduced to metallic silver, forming the visible image, while unexposed crystals are removed during fixing. Gelatin simply serves as the binder that suspends and supports the crystals; it is not light-sensitive. Calcium tungstate crystals, on the other hand, are phosphor particles used in older intensifying screens to convert X-ray energy to light, which then exposes the film indirectly. Lead oxide crystals aren’t used as the film’s light-sensitive coating.