Nuclear energy chronology: 1896-1945

1896 Becquerel in France discovers unstable (radioactive) atoms.

Thomson in England proves existence of electron.

1903 Rutherford and Soddy in Canada and P. Curie in France discover that radium contains vast stores of energy.
1905 Einstein in Switzerland states equivalence of mass and energy.
1911 Rutherford in England finds that mass of atoms is concentrated in nucleus.
1914-1918 First World War.
1919 Rutherford causes transmutation from one stable chemical element into another, by bombardment with alpha particles.
1929 Start of Great Depression.
1932 Chadwick in England discovers the neutron.

Cockcroft and Walton in England produce nuclear transformations by bombardment with artificially accelerated particles.
1933 Hitler seizes power in Germany.
1934 Curie and Joliot in France produce nuclear transformations by alpha-particle bombardment ("artificial radioactivity").

Szilard, in England as a refugee from German racial persecution, envisages a possible nuclear bomb. But most scientists doubt that usable energy could be extracted from the nucleus.

Fermi and co-workers in Italy produce nuclear transformations by neutron bombardment. They also produce fission but fail to recognize it.
1935-1937 Hahn, Meitner and Strassmann in Germany investigate products of neutron bombardment of uranium. They assume that these products are transuranian elements (i.e. slightly heavier than uranium).
Curie and Savitch in France find a substance seemingly identical to lanthanum among the products of uranium bombarded by neutrons.
Sept. Munich crisis; Hitler "appeased" with part of Czechoslovakia.
Dec. Hahn and Strassmann come to the unexpected conclusion that the uranium products include barium and lanthanum, elements half the atomic weight of uranium. They inform Meitner, now a refugee in Sweden.
Christmas Frisch visits his aunt, Meitner; they interpret the Hahn-Strassmann result as a splitting of the uranium nucleus in two. Hahn, in close touch by letter, comes to the same conclusion.
6 Jan.
Hahn-Strassmann paper published in Naturwissenschaften.
6-13 Jan. Frisch, returning to Bohr's Institute for Theoretical Physics in Copenhagen, discusses fission with Bohr, who leaves with Rosenfeld to visit the U.S. Frisch experimentally verifies the occurrence of fission.
16 Jan. Bohr arrives in New York; his news of fission is passed to physicists at Columbia University, including Fermi, who has just emigrated from Italy.

Issue of Naturwissenschaften containing Hahn-Strassmann paper reaches Joliot in Paris.
26 Jan. Fission verified experimentally by Dunning, Slack and Booth at Columbia and independently by Joliot.
Hahn-Strassmann paper reaches U.S.

Bohr and Fermi discuss fission in public at physics conference in Washington, D.C.

Experiments to verify fission begin at University of California at Berkeley and many other places.
Feb. Many physicists think fission may possibly be used to release large amounts of energy in a chain reaction. This would be possible only if several neutrons are emitted in each fission (these neutrons could then go on to provoke further fissions).
8 March Halban, Joliot and Kowarski in Paris complete experiment showing that some neutrons are emitted in fission.
15 March At Columbia, Fermi, Anderson and Hanstein, and Szilard and Zinn, complete experiments which parallel the French work.

German troops seize the free remnant of Czechoslovakia.
April The Paris team, followed independently by the Columbia group, finds that two or three neutrons are emitted per fission: enough to make a chain reaction possible. Over Szilard's objections both groups publish their findings.

American, British, French, German, and Russian scientists all approach their respective governments to seek support for fission research and a watch on uranium supplies.
May-Aug. Most scientists doubt that a highly explosive chain reaction is possible, but a few are interested in a nuclear reactor as a power source for industry or submarines. Joliot's group conducts reactor experiments; Szilard attempts to raise funds for similar work in U.S.
Sept. World War II begins in Europe.

Bohr and Wheeler publish theory of fission; they show that only the isotope U-235 will fission easily. This is one of the last openly published papers on fission research.
Oct. Letter on military implications of uranium, drafted by Szilard and signed by Einstein, delivered to President Roosevelt. He sets up an advisory uranium committee.
Fermi and co-workers, supported by the uranium committee's funds, study the chances of making a reactor. Others at Columbia study ways to separate pure U-235 from natural uranium.

Frisch and Peierls, German refugees in England, realize that a devastating nuclear bomb made of pure U-235 is possible. They send a memorandum to the British government, which sets up an advisory committee.
June Fall of France. Halban and Kowarski join British fission workers and urge construction of a reactor.
Berkeley scientists discover plutonium, which like U-235 is fissionable.

Some scientists recognize that plutonium can be created in a nuclear reactor and then used to build a bomb.
July British committee recommends that Britain begin a large nuclear bomb project.
Sept.-Oct. Compton, Lawrence and others, encouraged by the British, urge U.S. government to begin a large bomb project. Roosevelt commits funds.
7 Dec. Pearl Harbor; U.S. enters war.
1942 German and Japanese empires reach maximum extent at battles of Stalingrad, E1 Alamein, Midway.
2 Dec. Fermi's group, now in Chicago under Compton's overall leadership, creates a self-sustaining fission chain reaction—the first nuclear reactor.
1943 German fission program restricted to a small scale for lack of resources; small Soviet and Japanese programs underway.

British scientists (with French refugees) join forces with U.S. Manhattan Project.
1944 Production of U-235 begins at Oak Ridge, Tennessee. Large reactors built at Hanford, Washington to produce plutonium.

Allies invade Europe through Normandy.
End of war in Europe. Intense fire-bombing destroys nearly all Japanese cities.
16 July First atomic bomb test, New Mexico.
6 Aug. U-235 bomb destroys Hiroshima.
9 Aug. Plutonium bomb destroys Nagasaki.
14 Aug. Japan surrenders.