1. Photographic film
• Radioactivity was and still is detected through the darkening of photographic film.
• Usually used in monitoring the levels of radiation exposure of workers in industries or research labs
• The darkening is caused by silver crystals forming as radiation is absorbed by the silver salts in the film
• Contains light-sensitive silver halide salts
• The amount of darkening on the film is a measure of the amount of radiation received by the worker
Erm, those are just straight out of my notes. When it comes to HSC however (I see you're doing it next year), I wouldn't exactly pick photographic film as one to base my answer on for radiation detection as you'll kinda be limited on your explanation. Learn geiger-muller counter and cloud chamber by heart.