The badge consists of two parts: photographic film and a holder. The film emulsion is black and white photographic film with varying grain size to affect its sensitivity to incident radiation such as gamma rays, X-rays and beta particles.
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. 2b1af7f3a8