Little Boy, the Hiroshima bomb, used of uranium with an average enrichment of around 80%, or of uranium-235, just about the bare-metal critical mass . When assembled inside its tamper/reflector of tungsten carbide, the was more than twice critical mass. Before the detonation, the uranium-235 was formed into two sub-critical pieces, one of which was later fired down a gun barrel to join the other, starting the nuclear explosion. Analysis shows that less than 2% of the uranium mass underwent fission;Glasstone and Dolan, Effects, pp. 12–13. When 454 g (one pound) of 235U undergoes complete fission, the yield is 8 kilotons. The 13 to 16-kiloton yield of the Little Boy bomb was therefore produced by the fission of no more than of 235U, out of the in the pit. Thus, the remaining , 98.5% of the total, contributed nothing to the energy yield. the remainder, representing most of the entire wartime output of the giant Y-12 factories at Oak Ridge, scattered uselessly.Compere, A.L., and Griffith, W.L. 1991. "The U.S. Calutron Program for Uranium Enrichment: History,. Technology, Operations, and Production. Report", ORNL-5928, as cited in John Coster-Mullen, "Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man", 2003, footnote 28, p. 18. The total wartime output of Oralloy produced at Oak Ridge by July 28, 1945, was . Of this amount, 84% was scattered over Hiroshima (see previous footnote).
little boy the hiroshima bomb used of uranium with an average enrichment of around 80% or of uranium-235 just about the bare-metal critical mass  when assembled inside its tamper/reflector of tungsten carbide the was more than twice critical mass before the detonation the uranium-235 was formed into two sub-critical pieces one of which was later fired down a gun barrel to join the other starting the nuclear explosion analysis shows that less than 2% of the uranium mass underwent fission;glasstone and dolan effects pp 12–13 when 454 g (one pound) of 235u undergoes complete fission the yield is 8 kilotons the 13 to 16-kiloton yield of the little boy bomb was therefore produced by the fission of no more than of 235u out of the in the pit thus the remaining  985% of the total contributed nothing to the energy yield the remainder representing most of the entire wartime output of the giant y-12 factories at oak ridge scattered uselesslycompere al and griffith wl 1991 "the us calutron program for uranium enrichment history technology operations and production report" ornl-5928 as cited in john coster-mullen "atom bombs the top secret inside story of little boy and fat man" 2003 footnote 28 p 18 the total wartime output of oralloy produced at oak ridge by july 28 1945 was  of this amount 84% was scattered over hiroshima (see previous footnote)