Photographic film in the form of thin, even layers of emulsion is spread on a thick paper support base. The emulsion consists of small silver halide crystals embedded in a gelatin matrix. When the badge is exposed to radiation, energy is transferred to the emulsion causing silver ions to cluster together. These silver clumps are called latent image centers. This film detects x and gamma rays, beta particles greater than 1 MeV, and neutron radiation, except fast neutrons.
Fast neutrons require a separate type of film.
The accuracy of film badges is plus or minus 10 mrem. There are two types of film badges. One badge monitors x, gamma and beta radiation. The other contains an additional film which is sensitive to neutrons. Each holder has filters on the from and back sides containing an open window, then plastic aluminum, cadmium, and lead filters.