How can radioactivity be controlled?
Radioactivity cannot be perceived by our senses (vision, smell, hearing, etc.) but can be detected by specialised apparatus. Thus researchers have perfected a whole panoply of detectors (film that becomes clouded, Geiger counters that crackle, etc.) sensitive to the different types of radioactive radiation. Analyses are taken regularly in the environment (rivers, sea, air, land), not far from nuclear sites, and the health of those working in this industry is checked regularly.
