Figure 4-7. Ion chamber.
4-13. FILM BADGE
The film badge is an example of a total dose detector. It is the device most
commonly used to detect and measure occupational radiation exposures. Precise
procedures concerning wearing and maintenance of film badges can be found in the
a. A film badge consists of a film packet in a film holder usually constructed of
plastic or metal. In the film packet are two pieces of photographic film. One has a
double emulsion, and one has emulsion on one side only. The single emulsion is of
prime importance when loading the film holder. The film may contain only an x-ray
sensitive emulsion, or it may be sensitive to x-rays, gamma rays, and beta particles.
Special films are available to detect and measure neutrons.
b. The film responds to radiation exactly as does radiographic film; ionization
occurs within the emulsion layer, bringing about a chemical sensitivity to developer
solution in those silver bromide crystals so ionized. Then the radiation dosage is
determined by the film density. Processing is carried out under extremely controlled
conditions by a central agency to ensure accurate and constant results.
c. The film badge should be worn according to the previously mentioned
directives, so refer to them for guidance. Generally it is worn on an area of the body
expected to receive the highest exposure, such as the chest. (Occasionally, it may be
advisable to wear an additional film badge to determine local exposure. An example
would be a wrist badge worn by a radiologist during fluoroscopy to check exposure to
that area.) The film badge should not be carried in a pocket or behind any obstruction
such as coins, combs, or cigarette packages as they tend to absorb radiation and
reduce the ultimate density reading of the film. Wearing of the film badge in conjunction
with a protective apron is described in the appropriate directive. X-ray specialists