What is the active material in a Film Badge device?

The active material in a Film Badge device is film emulsion. Film badges utilize a piece of photographic film that is sensitive to ionizing radiation. When radiation interacts with the film emulsion, it creates a latent image that is later developed, allowing for the measurement of exposure to radiation over a specified period. The degree of darkening of the film correlates with the amount of radiation exposure, making the film emulsion a crucial component of this type of dosimeter.

In contrast, other materials listed in the choices serve different functions. Aluminum oxide and lithium fluoride are typically associated with other types of dosimeters and are not used in film badges. An ionization chamber is a different type of radiation detection instrument, which works by measuring the ions produced in a gas by radiation, rather than relying on film. Understanding the function of film emulsion as the active sensing material distinguishes it from other options that do not apply to the technology of film badges.