Radioactivity was discovered in 1896 by Antoine Henri Becquerel, a French physicist. His discovery led to the important research of Pierre and Marie Curie and others. Radium and other radioactive elements were discovered, and much was learned about the nature and effects of radioactivity. About 1900 Ernest Rutherford discovered alpha and beta particles in radioactive emissions.

In 1934, Frdric and Irne Joliot-Curie discovered that when aluminum foil was bombarded with alpha particles, the foil continued to emit radiation after the bombardment was stopped. The foil was the first known artificial radioisotope. In the late 1930s, as the result of the work of a number of scientists, it was discovered that uranium fissioned (split into two approximately equal parts) when bombarded with neutrons. This discovery led to the atomic bomb and, later, to nuclear power.