Werner Heisenberg. The Theoretical Basis for the Generation of Energy from Uranium Fission [February 26, 1942]

Abstract

The following experimental findings were known when work was begun on the uranium problem within the framework of the Army Ordnance Office study group:[²]

• 1) Common uranium is a mixture of three isotopes: ²³⁸₉₂ U, ²³₉₂ U, and, ²³⁴₉₂ U,which occur in natural minerals approximately in the proportion 1: 1/140: 1/17000.

• 2) Uranium nuclei can be split, according to Hahn and Straf3mann, by neutron radiation. [3] Specifically, the ²³⁵₉₂ U nucleus can be split by neutrons at all (including low) speeds (Bohr);[4] and ²³⁸₉₂ U and ²³⁴₉₂ U nuclei can only be split by high-energy neutrons.

• 3) An energy of about 150 to 200 million electron-volts per atomic nucleus is released during fission. This energy is approximately 100 million times greater than the energy normally released per atom during chemical reactions. Moreover, every time an atomic nucleus is split, some neutrons are ejected from it.