Also to add on to this: there's three primary types of nuclear energy. Alpha, Beta, and Gamma. Gamma is the bad stuff. Beta is bad but can be blocked with simple containment like thin lead. Alpha is largely harmless and can't even pass through air. But if an alpha source gets into your body, your fucked. It's why radon gas is so dangerous. You breathe it in and it has direct access to blood vessels and is easily distributed through the rest of your body. Russia assassinated a dude a bunch of years back by hiding an alpha source in a piece of sushi he was eating