French physicist Antoine Henri Becquerel discovers natural radioactivity.
German-born scientist Albert Einstein publishes theory that matter and energy are equal.
British physicist Ernest Rutherford announces his discovery of the nucleus of the atom.
German Hans Geiger invents a radiation detector that bears his name.
Princeton University researcher Robert van de Graaff builds an early particle accelerator, the Van de Graaff generator.
American physicist Ernest Lawrence invents the cyclotron, which uses a magnetic field to accelerate atomic particles.
Italian-born US physicist Enrico Fermi proposes use of neutrons to split atoms.
German chemists Otto Hahn and Fritz Strassmann achieve first fission of uranium.
Einstein writes a letter to President Franklin D. Roosevelt, warning of the military uses of atomic energy.
US scientists receive $6,000 for atomic research.
The Manhattan Engineer District of the Army Corps of Engineers (The Manhattan Project) is organized to produce an atomic bomb.
Fermi and colleagues achieve first artificially created chain reaction at the University of Chicago on Dec. 2.
A laboratory directed by J. Robert Oppenheimer is created on an isolated mesa at Los Alamos, N.M.
Two methods of uranium enrichment, necessary to produce fissionable material, are developed: gas diffusion and an electromagnetic means.
Funding for the Manhattan Project has grown to $2 billion.
The first atomic bomb is exploded near Alamogordo, N.M., in a secret predawn test on July 16.