When X-rays interact in solid materials, electrons
are liberated altering the populations of electrons in
various energy levels. This alteration results in changes
that can be detected using various methods that
depend on the physical composition of the manufactured material. A familiar example is ®lm wherein silver bromide crystals of a few micrometers diameter are
distributed in a photographic emulsion. X-rays that
interact in a crystal move a sucient number of electrons that some of the silver ions in the crystal lattice
are converted into silver atoms. The presence of these
silver atoms in the crystal heightens the sensitivity of
that one crystal to chemical photographic processing.
The more silver bromide crystals that are sensitized by
X-rays, the darker the ®lm will be upon processing.
This mechanism has a long history of use in dosimetry,
as for example in personnel monitoring. The energy
dependence of ®lm as a dosimeter is compensated by
employing attenuation ®lters in the radiation badge
holder. While ®lm is a widely used dosimetry device, it
requires considerable perseverance to maintain acceptable reproducibility of the entire process, including
uniform ®lm sensitivity, chemical processing and optical density readout.