Marie and Pierre Curie discover Radium and Polonium. 1899 Rutherford discovered that Uranium emits alpha and beta particles. Villard discovers gamma rays. Becquerel notices a red area on his chest after carrying a vial of Radium.
Rutherford proposes a model of the atomic nucleus.
1919 Rutherford discovered that the structure of matter could be changed by bombarding it with alpha particles. George Hevesy conducts the first tracer studies using a radioisotope of Lead to study Lead metabolism in plants. Hevesy realized that radioisotopes do not affect the biochemical properties of atoms. Blumgart first used radioisotopes for a clinical diagnostic test. Anderson discovers the positron.