What happens to a film dosimeter as radiation exposure increases?

As radiation exposure increases, the film dosimeter becomes darker. This is due to the interaction between the radiation and the film's emulsion, which contains silver halide crystals. When exposed to radiation, these crystals undergo a chemical change that results in a latent image being formed on the film. The degree of darkening correlates with the amount of radiation exposure; higher exposure results in more interactions with the film, leading to greater development of the latent image during processing. Therefore, a film dosimeter serves as an effective means of measuring the radiation dose by visually indicating the level of exposure through the degree of darkness on the film after it has been processed.