Film dosimeter

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Film dosimeter in a sliding shadow cassette

Film dosimeters (colloquially also film badges or X-ray badges ) are devices for detecting ionizing radiation that use the blackening of photographic material due to the radiation. They are used in the dose range between 0.1 mSv and 1 Sv and are suitable for X-rays and gamma rays between 20 keV and 3 MeV. Dose determination with film dosimeters is a storing and integrating process. By using different radiation converters (filters) in the housings (clip-on badge), these dosimeters can also be used for other types of radiation such as alpha radiation , beta radiation and neutron radiation .

construction

There are different types of film dosimeters available on the market, so there is no uniform structure of a film dosimeter. The film dosimeter used and approved in Germany is manufactured by the Agfa company. The polyethylene dosimeter cover contains two detectors, an insensitive film (u-eFilm) for high doses and a sensitive film (e-film) for low doses. There is also an intermediate layer of paper to separate the detectors.

The film dosimeter is carried on the body in a cassette that contains filter elements made of various metals. These filters make it possible to determine the angle of the incident radiation and also serve to be able to measure tissue-equivalent values ​​among the filter elements.

evaluation

Before the evaluation, the films are removed from the dosimeter cover and developed. Since the detectors are extremely light-sensitive, the unpacking process must be done in a darkroom. After unpacking, the films are passed through a developing bath. Due to the chemical development process, blackening becomes visible on the film where the film has come into contact with ionizing radiation. To be able to determine the dose on the film, the optical density is measured using a densitometer . The radiation protection officer is informed of the result of the evaluated dose .

application

Film dosimeters are used in personal dosimetry , in particular for the monitoring of people exposed to radiation by official measuring stations.

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