Personnel dosimetry film badges are commonly used
to measure and record radiation exposure due to gamma rays, X-rays
and beta particles. The detector is, as the name implies, a piece
of radiation sensitive film. The film is packaged in a light proof,
vapor proof envelope preventing light, moisture or chemical vapors
from affecting the film.
A special film is used which is coated with two different emulsions. One side is coated with a large grain, fast emulsion that is sensitive to low levels of exposure. The other side of the film is coated with a fine grain, slow emulsion that is less sensitive to exposure. If the radiation exposure causes the fast emulsion in the processed film to be darkened to a degree that it cannot be interpreted, the fast emulsion is removed and the dose is computed using the slow emulsion.
The film is contained inside a film holder or badge. The badge incorporates
a series of filters to determine the quality of the radiation.
Radiation of a given energy is attenuated to a different extent
by various types of absorbers. Therefore, the same quantity of
radiation incident on the badge will produce a different degree
of darkening under each filter. By comparing these results, the
energy of the radiation can be determined and the dose can be
calculated knowing the film response for that energy. The badge holder also contains an open window to
determine radiation exposure due to beta particles. Beta particles
are effectively shielded by a thin amount of material.
The major advantages of a film badge as a personnel monitoring
device are that it provides a permanent record, it is able to
distinguish between different energies of photons, and it can measure
doses due to different types of radiation. It is quite accurate
for exposures greater than 100 millirem. The major disadvantages are that it must be developed and read
by a processor (which is time consuming), prolonged
heat exposure can affect the film, and exposures of less than
20 millirem of gamma radiation cannot be accurately measured.
Film badges need to be worn correctly so that the dose they receive
accurately represents the dose the wearer receives. Whole body badges are worn on the body between
the neck and the waist, often on the belt or a shirt pocket. The clip-on badge is worn most often when performing X-ray or
gamma radiography. The film badge may also be worn when working around a low curie source. Ring badges
are worn on a finger of the hand most likely to be exposed to
ionizing radiation. A LIXI system with its culminated and directional beam would
be one example where monitoring the hands would be more important
than the whole body.