Film badges, and film badge dosimeters, are small portable devices for monitoring cumulative radiation dose due to ionizing radiation. The principle of operation is similar to X-ray pictures. The badge consists of two parts: photographic film and a holder. The film is contained inside a badge. The piece of photographic film is sensitive material, and it must be removed monthly and developed. The more radiation exposure, the more blackening of the film. The blackening of the film is linear to the dose, and doses up to about 10 Gy can be measured. Film badge dosimeters apply to situations where real-time information is not needed. Still, accumulated dose monitoring records are desired for comparison to field measurements or for assessing the potential for long-term health effects. In dosimetry, the quartz fiber and film badge types are superseded by TLDs and EPDs (Electronic Personal Dosimeter).
Film badge dosimeters are for one-time use and cannot be reused. A film badge dosimeter is a dosimeter worn at the body’s surface by the person being monitored, and it records the radiation dose received. The film badge measures and records radiation exposure due to gamma rays, X-rays, and beta particles. The badge incorporates a series of filters (lead, tin, cadmium, and plastic) to determine the radiation quality. The filters use various densities of plastic or even label material to monitor beta particle emission. It is typical for a single badge to contain a series of filters of different thicknesses and materials; the precise choice may be determined by the environment to be monitored.
Examples of filters:
- An open window makes it possible for weaker radiations to reach the film.
- A thin plastic filter that attenuates beta radiation but passes all other radiations
- A thick plastic filter passes all but the lowest energy photon radiation and absorbs all but the highest beta radiation.
- A dural filter progressively absorbs photon radiation at energies below 65 keV and beta radiation.
- A tin/lead filter of a thickness that allows an energy-independent dose response of the film over the photon energy range 75 keV to 2 MeV.
- A cadmium lead filter can be used for thermal neutron detection. The capture of neutrons ((n, gamma) reactions) by cadmium produces gamma rays which blacken the film, thus enabling assessment of exposure to neutrons.
