Jaros, Nagamiya, and Steiner reply: We thank Maurice Goldhaber for sharing with us his entertaining account of the circumstances surrounding “the bet.” We also thank Jeremy Bernstein for his clarification of our statements about the spontaneous fission results obtained by Emilio Segrè's group at Los Alamos. Our very brief comments about spontaneous fission were based on Segrè's autobiography. With respect to the effect of cosmic rays, Segrè writes,
Among other things, we found that the “spontaneous” fission at Los Alamos was greater than at Berkeley, which was not surprising because cosmic-ray neutrons, more abundant at a high altitude than at Berkeley, were obviously responsible for the effect. We had only to screen the chambers suitably to make it disappear. 1
The impact of spontaneous fission on bomb design is addressed in his next paragraph:
We soon recognized that Pu239 had a rate of spontaneous fission high enough to interfere seriously with the proposed methods of bomb assembly through pre-detonation…. Our results brought the Los Alamos lab to a real crisis…. Spontaneous fission in plutonium was so frequent that the plutonium alternative for making a bomb was excluded unless one could invent and develop a totally different assembly method. 1
