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The History of Nuclear Research


June - Rutherford creates oxygen from nitrogen.


Rutherford speculates on the existence of the neutron at the Royal Society.


November - Urey discovers deuterium.


James Chadwick proves the existence of neutrons, using alpha particles striking a beryllium foil. He determines their mass by measuring the recoil tracks of known atoms of the rarified gas in his cloud chamber.  

John Cockcroft and E. T. S. Walton of Great Britain split the atom on a linear accelerator

Leo Szilard reads H.G. Wells' novel, The World Set Free, in which Wells prophecies an atomic war in which the major cities of the world are destroyed.


Adolph Hitler becomes Chancellor of Germany.

Leo Szilard, a Hungarian physicist who took refuge in London from Nazi Germany, reads about a speech in which Lord Rutherford ridiculed the idea of using the transformation of atoms as a source of power. Szilard realizes that, "if we could find an element which is split by neutrons, and which would emit two neutrons when it absorbs one neutron, such an element could sustain a nuclear chain reaction."  


Frederic and Irene Joliot-Curie of France discover artificial radioactivity, i.e. the radioactivity of atoms produced in transmutation experiments. 

Enrico Fermi of Italy irradiates uranium with neutrons. He believes he has produced the first transuranic element, but unknowingly achieves the world’s first nuclear fission. 

Leo Szilard files for patent amendments for "the liberation of nuclear energy for power production and other purposes through nuclear 'transmutation.' "He proposes a "chain reaction" for the first time.


Leo Szilard files patent amendment identifying uranium and bromine as "examples for elements from which neutrons can liberate multiple neutrons..."

When Szilard learns that the only way for his patents on liberating nuclear energy can be kept secret is to assign them to an agency of the British government he offers them to the British War Office.

The British War turns down
Leo Szilard's offer to give them his patents on nuclear energy stating, "There appears to be no reason to keep the specification secret so far as the War Department is concerned."


Leo Szilard's offer to turn over patents on nuclear energy, in order to keep them secret, is accepted by British Admiralty.


Otto Hahn and Fritz Strassmann of Germany split the uranium atom by bombarding it with neutrons and show that the elements barium and krypton are formed. 

Lisa Meitner
conducts experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.

Lise Meitner and Otto Frisch of Austria announce theory of nuclear fission.

Frederic Joliot
demonstrates the possibility of splitting the atom of uranium isotope 235.

Hans A. Bethe, a German-born physicist, recognizes that the fusion of hydrogen nuclei to form deuterium releases energy. He suggests that much of the energy output of the Sun and other stars results from energy-releasing fusion reactions in which four hydrogen nuclei unite and form one helium nucleus.

Otto Frisch detects fission fragments in an ionization chamber. He adopts the term "

First experimental fission in U.S. takes place at Columbia University.

Niels Bohr announces discovery of fission at a conference in theoretical physics at George Washington University in US

Upon hearing of discovery of fission,
Robert Oppenheimer immediately grasps the possibility of atomic bombs.

Leo Szilard writes to Enrico Fermi describing the concept (uranium lattice in carbon) for creating a chain reaction.

Albert Einstein's first letter to President Franklin Roosevelt leads to the formation of the Committee on Uranium. The letter, originally drafted by Leo Szilard states "that the element uranium may be turned into a new and important source of energy in the immediate future. Certain aspects of the situation which has arisen seem to call for watchfulness and, if necessary, quick action on the part of the Administration." After the bombing of Hiroshima, Einstein states, "I could burn my fingers that I wrote that first letter to Roosevelt."

Einstein and Szilard warn Roosevelt

The fear of a German atomic bomb troubled Leo Szilard. On August 2, 1939, he and Edward Teller drove to Long Island, New York. They went to ask Albert Einstein to sign a letter to President Roosevelt outlining the dangers of a German bomb project.

September 1
Germany invades Poland. World War II begins.


It was not until July 13, 1942, in the midst of World War II, that the United States undertook the Manhattan Project to develop an atomic bomb. By December 2, a Manhattan Project team headed by Enrico Fermi produced the first artificial fission reaction at the University of Chicago. Three years after its inception, the Manhattan Project achieved its goal of developing an atomic weapon.

Construction of CP-1, or Chicago Pile Number One, was done under the football stadium in an abandoned squash court. On December 2, 1942, mankind first harnessed the energy of the atom. Fermi's pile produced only 1/2 watts of power. But that was all the power the United States needed to start the next phase of the bomb's development.

The pile contained 771,000 pounds of graphite, 80,590 pounds of uranium oxide and 12,400 pounds of uranium metal when it went "critical." It cost about $1 million to produce and build. The pile took the form of a flattened ellipsoid which measured 25 feet wide and 20 feet high.


June 3 - German scientists fail to observe neutron multiplication in the reactor in Hamburg.


January - Based on experiments with a natural uranium reactor, the Germans reject graphite as a moderator.
July - British 'Maud' Committee reports that a weapon could be made with 10 kg of U-235; US Academy of Sciences endorses bomb program.


May - Heisenberg and Dopel observe the first multiplication of neutrons.
December 2 - First nuclear chain reaction at Chicago's Stagg Field by Fermi.


March 15 - Oppenheimer moves the bomb development to Los Alamos.


August 26 - Bohr presents his memorandum on intentional control of nuclear weapons to Roosevelt.
November - First batch of spent fuel obtained from Hanford reactors.
November - Goudsmit's ALSOS mission obtains documents which imply that the German's rate of progress toward a bomb had diminished.


January - First Pu reprocessing production run at Hanford
January 20 - First U-235 separated at Oak Ridge.
June 11- The Franck Report was sent to the Secretary of War.
July 16 - US explodes first atomic bomb, the Trinity test, at Alamogordo.

Trinity Test

On July 16, 1945, at 5:29:45 AM, a light "brighter than a thousand suns," filled the valley. As the now familiar mushroom cloud rose in to the sky, Oppenheimer quoted from Hindu scripture, the Bhagavad-gita, "Now I am become death, the destroyer of worlds." The world had entered the nuclear age.

The "Gadget" had a yield equivalent to 19 kilotons of TNT. "Fat Man," the bomb dropped on Nagasaki was identical in design to the "Gadget."

August 6,9 - Atomic bombs dropped on Hiroshima and Nagasaki.

Little Boy Bomb

A QuickTimeVR model of the Little Boy Bomb

In essence, the Little Boy design consisted of a gun that fired one mass of uranium 235 at another mass of uranium 235, thus creating a supercritical mass. A crucial requirement was that the pieces be brought together in a time shorter than the time between spontaneous fissions. Once the two pieces of uranium are brought together, the initiator introduces a burst of neutrons and the chain reaction begins, continuing until the energy released becomes so great that the bomb simply blows itself apart.

This is a replica of the bomb that was dropped over Hiroshima, Japan on August 6, 1945.


Fat Man

A QuickTimeVR model of the Fat Man Bomb

The rapid spontaneous fission rate of plutonium 239 necessitated that a different type of bomb be designed. A gun-type bomb would not be fast enough to work. Before the bomb could be assembled, a few stray neutrons would have been emitted, and these would start a premature chain reaction leading to a great reduction in the energy released.

Seth Neddermeyer, a scientist at Los Alamos, developed the idea of using explosive charges to compress a sphere of plutonium very rapidly to a density sufficient to make it go critical and produce a nuclear explosion. This is a replica of the bomb that was dropped over Nagasaki, Japan on August 9, 1945.

Fat Man Specifications


10 feet 8 inches
5 feet
10,000 lbs
22 kilotons


The Atomic Bomb Cloud over Nagasaki

On August 9, 1945, the American B-29 bomber, Bock's Car left Tinian carrying Fat Man, a plutonium implosion-type bomb. The primary target was the Kokura Arsenal, but upon reaching the target, they found that it was covered by a heavy ground haze and smoke, pilot Charles Sweeney turned to the secondary target of the Mitsubishi Torpedo Plant at Nagasaki.

Of the 286,00 people living in Nagasaki at the time of the blast, 74,000 were killed and another 75,000 sustained severe injuries.



World War II ended in Europe on May 8, 1945, less than a month after the death of President Franklin Roosevelt, but plans for the development and use of atomic weapons continued.

At at 5:29 a.m. on July 16, 1945, the United States conducted the world's first nuclear test explosion at Alamogordo, New Mexico. The Nuclear Age was born, a product of the fear, violence, and suffering of World War II. J. Robert Oppenheimer, director of the Los Alamos Laboratory, recalled the following passage from the Bhagavad Gita upon witnessing the explosion: "I am become death, the destroyer of worlds"

Within a month, nuclear weapons were used to destroy the Japanese cities of Hiroshima and Nagasaki. When he received word of the bombing of Hiroshima, President Truman exclaimed, "This is the greatest day in history!"