So there’s four types of radiation: alpha, beta, gamma, and neutron. When you’re talking about radioactive materials, it’s almost exclusively the first three. In addition to the inherent danger of the object itself, there’s also the danger of radioactive contamination: not making other things radioactive, but shedding bits of themselves as dust and then that dust getting on other things, or getting ingested/inhaled by humans.

Active fission reactions, like what goes on in the core of a nuclear reactor (or perhaps messing around with some plutonium and a screwdriver), produce neutron radiation. Neutrons can make other things radioactive, via a process called “neutron activation”, whereby the neutrons bind to the material and change some of the atoms into radioactive isotopes.

I hope that helps, and feel free to ask me anything else about radiation. I have some education about it thanks to my job, and I’m always happy to help other people understand it more as well.