Unstable nuclei give out three main types of radiation. Each one is a different thing.
An alpha particle is the same as a helium nucleus. It is made of two protons and two neutrons, so it has a mass number of 4 and a positive charge. A beta particle is a fast-moving electron. It is emitted from the nucleus, not from the electron shells around it, when a neutron in the nucleus changes into a proton. It has a negative charge.
Alpha and beta radiation are both particles. A gamma ray is not a particle. It is electromagnetic radiation, a wave like light or X-rays but with a much higher frequency. It has no mass and no charge.
