I will try to explain it as best as I can. Radioactive material decays as particles are emitted. If it has a long half-life, that pretty much means that the en

I will try to explain it as best as I can. Radioactive material decays as particles are emitted. If it has a long half-life, that pretty much means that the energy is being released rather slowly. In other words, just don't go poking at it and you'll be fine. On the othe hand, stuff with a short half-life means that atoms are decaying rapidly. Particles are being knocked off with great rapidity. That stuff is much more dangerous, in the now. It is transferring energy, in a harmful form, quickly. A long half-life means don't go poking at it for a while. A short half-life means you probably should consider containing it really well. We store both safely because we know people like to poke stuff, and it is harmful. It's just that the scary long half-lives only tell part of the story and many people seem to think those are the more problematic. Disclaimer, I'm a mathematician, not a physicist. However, I've taken a whole lot of physics courses. Someone can probably explain this better than I.