We talked about alpha particles, beta particles, and gamma rays, which are types of ionizing radiation. You often see pictures like the one up above, which show you what each of these types of radiation can go through.
Alpha particles are heavy and big, and won’t go through paper, clothes, or skin. Beta particles will go through those things, but are stopped by a relatively thin sheet of metal.
Gamma rays, however, are rays not particles. (Well, more properly they’re photons, like light. So they’re kind of particles.) They are only stopped by a massive thickness of heavy material, like the lead around a bank vault or several feet of dirt.
You might thus conclude that gamma radiation is the most dangerous and alpha radiation is the least? Well …
