Some atoms have unstable nuclei because of 'extra' neutrons. Carbon-14 has an unstable nuclei - it has 6 protons and 8 neutrons i. e. extra neutrons! To become more stable, these unstable nuclei throw particles out - this process is called decay. Carbon-14 is radioactive. It is a radioisotope and when it decays it gives out radiation. All radioisotopes eventually turn into stable atoms by giving out radiation. Decay is a random process. Radiation consists of three types of particles: alpha beta gamma An alpha particle consists of two protons and two neutrons. They can be stopped with paper, slows down quickly in air. A beta particle is a fast electron. Can travel 20-30cm in air and through thin sheets of paper and metal. A gamma ray is a high-energy ray. Can travel deep into the body, only thick blocks of concrete or lead can stop it penetrating further. Radiation can cause cells to mutate - can lead to cancer. We are surrounded by low-level radiation from rocks and cosmic rays called background radiation. Radiation can be useful: Used as tracers To kill germs Cancer treatment Carbon dating - to find the age of once living organisms. Dating rocks.