Hiroshima Bomb's Explosive Yield Less than Reported

Paul Guinnessy reports that the explosive yield of the Hiroshima bomb was 20 kT (Physics Today, August 2002, page 23 ). However, that value is at variance with the most reliable ones in the open literature, in which one typically sees values of 12.5 to 15 kT.¹ The comprehensive calculation by John Malik gives the value of 15 kT, with an error of 20%.²

The 20-kT value was initially given by President Harry S. Truman in August 1945. Physicists at Los Alamos knew it was an overestimate that was based, perhaps, on information Truman had from the Trinity test. But the Trinity test data were for a different type of bomb--a plutonium implosion device, not the uranium gun-type model that was used on Hiroshima.

References

• 1. L. Badash, Scientists and the Development of Nuclear Weapons, Humanities Press, Atlantic Highlands, N.J. (1995), p. 54; S. Hoddeson et al., Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943-1945, Cambridge U. Press, New York (1993), p. 392; R. Rhodes, The Making of the Atomic Bomb, Simon & Schuster, New York (1986), p. 711.
• 2. J. Malik, The Yields of the Hiroshima and Nagasaki Nuclear Explosions, technical rep. no. LA-8819, Los Alamos National Laboratory, Los Alamos, N.Mex. (September 1985).