All substance are made of atoms . In some types of atom, the nucleus is unstable , and will decay into a more stable atom. This radioactive decay is completely spontaneous . This form of Lithium is not radioactive - it's just an example of a simple atom.
Most radioactive substances have many more particles in their nucleus.
When an unstable nucleus decays, there are three ways that it can do so. Many radioactive substances emit a particles and b particles as well as g rays. Click the button. Alpha particles are made of 2 protons and 2 neutrons . Alpha particles are relatively slow and heavy .