1903 The husband and wife team of Marie and Pierre Curie received the Nobel Prize in physics for their discovery of radium.

1911 Ernest Rutherford advances the planetary model of the atom.

1932 James Chadwick discovers the neutron.

1933
January 30: Adolf Hitler becomes chancellor of Germany.

Spring–Summer: Physicists James Franck, Edward Teller, Leo Szilard, Eugene Wigner, and Albert Einstein are persecuted by the Nazis for being Jewish and flee Germany for the United States.

1934
Enrico Fermi bombards uranium with neutrons and publishes his experimental results.

1938

November: Italian born Fermi receives Nobel Prize for physics in Sweden, and then emigrates to the United States to escape Itlian dictator Benito Mussolini’s anti-Semitic policies.

December: Otto Hahn and Fritz Strassmann, two German physicists, split uranium atom, creating lighter elements, energy, and more neutrons. Their discoveries would be the basis for devising the atomic bomb.

1939
January: Otto Frisch and Lise Meitner prove a "fission...