Question: How could you determine the amount of danger a nuclear substance has?

Ellen Gill answered on 16 Jun 2016:

What we look at is the energy levels of the radiation being given off, the activity levels (how frequently that radiation is being thrown out) and how deeply penetrating the type of radiation it is. Alpha radiation has very high energy levels but is easily stopped by the dead outer layers of skin so is only a problem if it gets inside you. Beta and gamma radiation can penetrate human bodies but have less energy (although it depends on the exact radionuclide).
When we talk about radiation doses, we’re talking about the ionising radiation energy sent into your body as a result of all three of those things. The size of the dose and the time it’s received over determine how severe the dose is.
Sort of like how having an apple thrown at your head once every hour would be annoying, but having 10 apples simultaneously fired into your face at 50mph would really, really hurt.