Nuclear Physics is the scientific study of the forces, reactions and internal structures of atomic nuclei. It is the field of physics that studies the building blocks and interactions of atomic nuclei. In 1905 Albert Einstein formulated the idea of mass energy equivalence. While the work on radioactivity by Becquerel, Pierre and Marie Curie Predates this, an explanation of the source of the energy of radioactivity would have to wait for the discovery that the nucleus itself was composed of smaller constituents, the nucleons. The practical applications of nuclear physics in modern society are enormous and unbelievably varied, ranging from nuclear weapons and the production of nuclear power to diagnosis and treatment in medicine.