1939 to 1941: Investigating Nuclear Weapons

1939 to 1941: Investigating Nuclear Weapons

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May 27, 1940

Louis Turner mails Leo Szilard a manuscript arguing that the isotope of element 94 with 239 nucleons, not yet discovered, should be highly fissionable like uranium-235, and could be manufactured by bombarding uranium-238 with neutrons, to form uranium-239. The same day, Edwin McMillan and Philip Abelson submit the report "Radioactive Element 93" to Physical Review describing their discovery of element 93, neptunium, produced by bombarding uranium with neutrons. Britain subsequently protests the publication as a violation of wartime secrecy.

May 1940

George Kistiakowsky suggests gaseous diffusion as a possible means for producing uranium-235 to Vannevar Bush during a meeting at Carnegie Institution.

April 27, 1940

Second meeting of Lyman Briggs' The Uranium Committee. Briggs' decision is that neither research on fast fission, nor work on building a critical uranium-graphite assembly, should begin until the small scale lab experiments, just getting underway, are finished.

April 10, 1940

First meeting of the British committee (later code-named the MAUD Committee) organized by Henry Tizard to consider Britain's actions regarding the "uranium problem". Research into isotope separation and fast fission is agreed upon.

March, 1940

After much prodding by Leo Szilard, Lyman Briggs, head of the Uranium Committee, finally releases a promised $6,000 budgeted for conducting neutron experiments with Enrico Fermi at Columbia University.

February 1940

Otto Frisch and Rudolf Peierls, living in the United Kingdom, consider the possibility of fast fission in uranium-235. Based on a theoretical estimate of the fast fission cross section they estimate the critical mass of pure uranium-235 at "a pound or two", and that a large percentage could be fissioned before explosive disassembly. They also estimate the likely effects of the bomb, and possible assembly methods, as well as estimates of the feasibility of isotope separation.