The film badge dosimeter, or film badge, is a dosimeter used for monitoring exposure to ionizing radiation. A dosimeter is any device used to measure an individual's exposure to a hazardous environment particularly when the hazard is cumulative over long intervals of Time Radiation poisoning, also called " radiation sickness " or a " creeping dose " is a form of damage to organ tissue due to excessive exposure to Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation The badge requires two parts to be effective: photographic film, and a holder. This article is mainly concerned with Still photography film For Motion picture film please see Film stock.
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Description
The film 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 extends the exposure latitude to several orders of magnitude. An emulsion ( IPA: /ɪˈmʌlʃən/ is a mixture of two Immiscible (unblendable liquids Wide latitude is highly desirable as it allows quantitation of very large accidental exposures without degrading sensitivity to more usual low level exposure.
Holder
The holder may contain a number of filters that attenuate certain types of radiation, such that only the target radiation is monitored. Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy To monitor gamma rays or x-rays, the filters are metal, usually tin or lead. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions X-radiation (composed of X-rays) is a form of Electromagnetic radiation. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly To monitor beta particle emission, the filters use various densities of plastic. In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products 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 thicknesses 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. This places a minimum useful size on the holder and badge.
Usage
The badge is typically worn on the outside of clothing, around the chest or torso. This location monitors exposure of most vital organs and represents the bulk of body mass. In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument If protective clothing is worn (e. g. lead aprons or gloves) then the badge is worn underneath the protection to monitor the dose actually received by the operator.
Under special circumstances, where an operator may receive a high dose to one area of the body (e. g. the hands of a radiopharmacist) then additional monitoring of the area is required. For monitoring of hands, a miniature Thermoluminescent Dosimeter worn as a finger ring is usually used. A thermoluminescent dosimeter, or TLD is a type of Dosimeter.
The film badge is not widely used in the USA, having been replaced by multi-chip thermoluminescent dosimetry. The United States of America —commonly referred to as the A thermoluminescent dosimeter, or TLD is a type of Dosimeter. However, the FBD is the dominant dosimeter used in the rest of the world.
Special properties
The film badge has several advantages over other types of dosimetry:
Permanent record of exposure: The developed film is physical evidence of the radiation exposure. The film can be stored after developing and reading, and could be reviewed at a later date if there is a query over exposure.
Exposure pattern discrimination: A film badge offers limited discrimination between different patterns of exposure. A single exposure tends to leave sharp shadows on the film from the filters, whereas multiple small exposures at different angles will leave a rim of blurring around the filters. This may allow the linking of a dose with a specific incident and provides a degree of protection against tampering (e. g. deliberate exposure to a radiation source).
Radiation type detection: Use of multiple filters allows estimation of type of radiation (beta / gamma), and energy spectra. Additional filters can be added to detect neutron radiation (e. g. Cadmium). The sensitivity to low energy (<20keV) gamma/x radiation of film can be better than electronic dosimeters.
Further reading
Film Badge Dosimetry in Atmospheric Nuclear Tests (1989) at the National Academies Press
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