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A film badge dosimeter or film badge is a personal dosimeter used for monitoring cumulative radiation dose due to ionizing radiation.
The badge consists of two parts: photographic film and a holder. The film emulsion is black and white photographic film with varying grain size to affect its sensitivity to incident radiation such as , and .
After use by the wearer, the film is removed, developed, and examined to measure exposure. When the film is irradiated, an image of the protective case is projected on the film. Lower energy are attenuated preferentially by differing absorber materials. This property is used in film dosimetry to identify the energy of radiation to which the dosimeter was exposed. Some film dosimeters have two emulsions, one for low-dose and the other for high-dose measurements. These two emulsions can be on separate film substrates or on either side of a single substrate. Knowing the energy allows for accurate measurement of radiation dose.
The device was developed by Ernest O. Wollan whilst working on the Manhattan Project, though photographic film had been used as a crude measure of exposure prior to this.
Though film dosimeters are still in use worldwide there has been a trend towards using other dosimeter materials that are less energy dependent and can more accurately assess radiation dose from a variety of radiation fields with higher accuracy.
To monitor or , the filters are metal, usually lead, aluminum, and copper. To monitor beta decay, the filters use various densities of plastic or even label material. It is typical for a single badge to contain a series of filters of different thicknesses and of different materials; the precise choice may be determined by the environment to be monitored. The use of several different materials allows an estimation of the energy/wavelength of the incident radiation.
Filters are usually placed on both the back and front of the holder, to ensure operation regardless of orientation. Additionally, the filters need to be sufficiently large (typically 5 mm or more) to minimize the effect of radiation incident at oblique angles causing exposure of the film under an adjacent filter. Normally it is worn at chest height under a lead apron to measure the radiation level the entire body has received.
The dose measurement quantity, personal dose equivalent Hp(d), is defined by the International Commission on Radiological Protection (ICRP) as the dose equivalent in soft tissue at an appropriate depth, d, below a specified point on the human body. The specified point is specific to the position where the individual’s dosimeter is worn.ICRP publication 103 - glossary Tissue depth of interest include the tissue depth of the live layer of skin (0.07 mm), lens of the eye, (0.30 cm), and "deep" dose, or dose to the whole body (1.0 cm).
The film badge is still widely used, but is being replaced by thermoluminescent dosimeters (TLDs), aluminium oxide based dosimeters, and the electronic personal dosimeter (EPD).
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