To understand radioactive material, one needs know a little bit about the composition of matter. Every material is made up of tiny particles called atoms. At the middle of each atom is a “nucleus” made up of “protons” and “neutrons”. The number of protons in the nucleus determines the type of “element”. If the number of protons and neutrons is properly balanced, the atom will be “stable”. The oxygen that we breathe is an example of stable atom. It will normally contain 8 protons and 8 neutrons, and is referred to as “Oxygen-16”, where 16 refers to the total number of protons and neutrons in each nucleus.
However, some combinations of protons and neutrons may not be stable and will “decay” by emitting “radiation”, in the form of particles and energy. For example, the combination of 8 protons and 7 neutrons is another form or “isotope” of oxygen, known as “Oxygen-15”. It is unstable or “radioactive”. It emits a positively charge particle known as a “positron” as well as gamma rays. In doing so, one of the protons in the nucleus is converted to a neutron, so that the newly created nucleus contains 7 protons and 8 neutrons. Because there is now one fewer proton, the new atom is actually “Nitrogen-15”. This combination is stable.
Radioactive isotopes, also known as radioisotopes, exist all around us naturally, and can even be found in elements such as carbon, hydrogen, and cobalt. They can be found in the ground, for example, in the form of Uranium and its decay products such as radon, in equilibrium with all living things in the form of Carbon-14, and directly in the body in the form of Potassium-40. Radioactive isotopes may also be produced artificially. For example, Oxygen-15 is often used for medical diagnostic purposes and is specially produced in a device called a “cyclotron”