Film badge dosimeter

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The film badge dosimeter,[1] 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 or dental X-ray film, and a holder.[2] The film is removed and developed to measure exposure. The film badge is used to measure and record radiation exposure due to gamma rays, X-rays and beta particles.[3] It is essentially useless for measuring neutron radiation. The device was developed by Ernest O. Wollan whilst working on the Manhattan Project,[4] though photographic film had been used as a crude measure of exposure prior to this.

It is now being replaced by more modern dosimeters.


Description[edit]

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 extends the dynamic range 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[edit]

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 rays or x-rays, the filters are metal, usually aluminum or copper. To monitor beta particle emission, the filters use various densities of plastic. 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[edit]

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.

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 usually given by the position where the individual’s dosimeter is worn.[5]

The film badge is now not widely used, being largely replaced by such as the Thermoluminescent Dosimeter (TLD) and the Electronic Personal Dosimeter (EPD).

See also[edit]

References[edit]

  1. ^ "film badge dosimeter". Britannica.com. Retrieved 2012-05-27. 
  2. ^ "film badge dosimeter". Britannica.com. Retrieved 2012-05-27. 
  3. ^ "Film badgespublisher=NDT Resource Center". Retrieved 2012-05-27. 
  4. ^ Pardue, L. A.; Goldstein, N; Wollan, E. O. (1948). "Photographic film as a pocket radiation dosimeter". Atomic energy in biophysics, biology and medicine 1 (5): 169. PMID 18878757.  edit
  5. ^ ICRP publication 103 - glossary

Further reading[edit]

Film Badge Dosimetry in Atmospheric Nuclear Tests (1989) at the National Academies Press