Nuclear physics is the study of the nucleus of atoms. The nucleus is at the center of the atom, and is made up of nucleons (protons and neutrons). The protons of the neucleus define what element it is (i.e. hydrogen, helium, oxygen, etc.). The neutrons define what isotope it is. An isotope is a name for an element with a certain number of neutrons in it. For example, Carbon's most common isotope is Carbon-12, which has six protons and six neutrons. However, carbon also has an isotope caled carbon-14. This still has six protons, but it has an extra two neutrons. This means that carbon-12 and carbon-14 are the same element, but different isotopes. As with all other kinds of physics, nuclear physics also has a lot to do with forces. In nuclear physics, there are two very important forces that are studied the most: the strong interaction and the weak interaction. The strong interaction is a force that attracts protons to neutrons. This allows neuclei to form and stay together. The weak interaction allows neutrons to decay into protons and electrons. When this happens, it is called beta decay, and it is one of the three ways that atoms can become less radioactive.