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1938 to 1939: Discovering Fission

1938 to 1939: Discovering Fission

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August 31, 1939

Niels Bohr and John A. Wheeler publish a theoretical analysis of fission. This theory implies that uranium-235 is more fissile than U-238, and that the isotope of the undiscovered element 94 with 239 nucleons is also very fissile. These implications are not immediately recognized.

June 1939

Enrico Fermi and Leo Szilard submit a paper to Physical Review describing subcritical neutron multiplication in a lattice of uranium oxide in water, but it is clear that natural uranium and water cannot make a self-sustaining reaction.

February 5, 1939

Niels Bohr realizes that uranium-235 and uranium-238 must have different fission properties, uranium-238 could undergo fission by fast neutrons but not slow ones, and that uranium-235 accounted for observed slow fission in uranium.