What are the 3 main types of radiation?

The three main types of radiation are alpha, beta and gamma radiation. Alpha particles are the largest, two protons and two neutrons bound together (so they have a +2 positive charge). They are the most ionising - because of their charge they pull electrons off atoms as they pass. Because of their relatively large mass they don't travel very fast or very far, and they can't go through most materials - they have low "penetration". They can be stopped by a sheet of paper or human skin. Beta particles are fast-moving electrons that get shot out of nuclei. They have a -1 charge so they are less ionising than alpha particles. But they can penetrate straight through a human hand or a sheet of paper. They can be stopped by a thin sheet of aluminium. Gamma radiation is in the form of electromagnetic waves (like light, or UV radiation, but with a much higher energy), with no mass and no charge. They are less ionising than Beta particles but move at the speed of light, and are highly penetrating. They can pass through flesh and thin metal, so it takes several cm of lead or several metres of concrete to stop them.