A film badge dosimeter or film badge is a personal

dosimeter A radiation dosimeter is a device that measures dose uptake of external ionizing radiation. It is worn by the person being monitored when used as a personal dosimeter, and is a record of the radiation dose received. Modern electronic personal d ...

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 gamma rays, X-rays and beta particles. 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 photons 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 Ernest Omar Wollan (November 6, 1902 – March 11, 1984) was an American physicist who made major contributions in the fields of neutron scattering and health physics. Biography Wollan was a native of Glenwood, Minnesota. After earning a bachelor' ...

whilst working on the

Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...

, 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.

Description

The silver film emulsion is sensitive to radiation and once developed, exposed areas increase in optical density (i.e. blacken) in response to incident radiation. One badge may contain several films of different sensitivities or, more usually, a single film with multiple emulsion coatings. The combination of a low-sensitivity and high-sensitivity

emulsion An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Altho ...

extends the

dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of Signal (electrical engineering), signals, like sound and light. It is measured ...

to several orders of magnitude. Wide dynamic range is highly desirable as it allows measurement of very large accidental exposures without degrading sensitivity to more usual low level exposure.

Film holder

The film holder usually contains a number of filters that attenuate radiation, such that radiation types and energies can be differentiated by their effect when the film is developed. To monitor

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

s or

x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s, the filters are

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

, usually lead,

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

, and

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

. To monitor beta particle emission, the filters use various densities of

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

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.

Usage

The badge is typically worn on the outside of clothing, around the chest or torso to represent dose to the "whole body". This location monitors exposure of most

vital organ In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...

s and represents the bulk of body mass. Additional dosimeters can be worn to assess dose to extremities or in radiation fields that vary considerably depending on orientation of the body to the source. The dose measurement quantity, personal dose equivalent Hp(d), is defined by the

International Commission on Radiological Protection The International Commission on Radiological Protection (ICRP) is an independent, international, non-governmental organization, with the mission to protect people, animals, and the environment from the harmful effects of ionising radiation. Its r ...

(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 cm), 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 dosimeter A thermoluminescent dosimeter, or TLD, is a type of radiation dosimeter, consisting of a piece of a thermoluminescent crystalline material inside a radiolucent package. When a thermoluminescent crystal is exposed to ionizing radiation, it abso ...

s (TLDs), aluminium oxide based dosimeters, and the

electronic personal dosimeter The electronic personal dosimeter (EPD) is a modern electronic dosimeter for estimating uptake of ionising radiation dose of the individual wearing it for radiation protection purposes. The electronic personal dosimeter has the advantages over o ...

(EPD).

References

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Description

Film holder

Usage

See also

References

Further reading