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| Fig. 1: Szilard-Wigner letter signed by Einstein addressed to President Roosevelt. (Source: Wikimedia Commons) |
In January 1939, German scientists Otto Hahn and Fritz Strassmann published a paper on splitting uranium into barium, an element roughly half the size of uranium, by bombarding it with neutrons. Immediately after, Lise Meitner and Otto R. Frisch came out with a separate publication of how Neils Bohr's model of the atom could explain this division. [1] They coined the term fission to describe this process.
The fission process was discovered to not only release enormous amounts of energy but also emit neutrons. These secondary neutrons could collide with other atoms and release more neutrons, causing a chain reaction. [2] A controlled chain reaction makes it possible to generate large amounts of energy, and an uncontrolled chain reaction could result in an explosion magnitudes greater than conventional bombs. [3]
This discovery raised alarm across the scientific community internationally. However, scientists in different nations responded in vastly different manners. Those in the U.S. and the U.K. sought to perform research in private while those in Germany disseminated information freely. In June 1939, Siegfried Fluegge published a paper discussing German developments, stopping just short of saying bomb. He originally intended to show that Germany has nothing to hide. However, it produced the opposite effect and created a very real sense of urgency in the allied forces. [3] It also spurred interest among German authorities and the German Army provided funds to establish a research division headed by Dr. Kurt Diebner. [3]
Foreseeing the Third Reich using fission for military purposes, prominent American nuclear scientists Leo Szilard and Eugene Wigner drafted a letter to the U.S. government and convinced Albert Einstein to sign it. [4] This became the famous Einstein-Roosevelt letter of August 1939. With Hitler's blitzkrieg on Poland in September 1939, Roosevelt was forced to take the threat seriously and take action.
In October 1939, Roosevelt formally approved the Advisory Committee on Uranium. [4] In the spring of 1940, that committee became the National Research Defense Council headed by Vannevar Bush. [1] The Army Corps of Engineers then created a special division that would handle the construction needed of an atomic bomb. The division was headquartered in Manhattan, New York and was given the code name of Manhattan Engineering District, or what we now more commonly know as the Manhattan Project. [4]
© Allen Yu. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] O. Hahn, "The Discovery of Fission," Scientific American 198, No. 2, 6 (February, 1958).
[2] J. Lee, "The Manhattan Project," Physics 241, Stanford University, Fall 2012.
[3] F. G. Gosling, The Manhattan Project: Making the Atomic Bomb, U.S. Department of Energy, DOE/MA-0002 Revised, January 2010, pp. 3-5.
[4] J. Belanger, "The Manhattan Project," Physics 241, Stanford University, Spring 2013.
