The Making of the Atomic Bomb: 25th Anniversary Edition

by Richard Rhodes

“Just sort of playfully,” Frisch writes, he plugged 10-23 cm21265 into Peierls’ formula.1266 “To my amazement” the answer “was very much smaller than I had expected; it was not a matter of tons, but something like a pound or two.”1267 A volume less than a golf ball for a substance so heavy as uranium. But would that pound or two explode or fizzle? Peierls easily produced an estimate. The chain reaction would have to proceed faster than the vaporizing and swelling of the heating metal ball. Peierls calculated the time between neutron generations, between 1×2×4×8×16×32×64 . . . , to be about four millionths of a second, much faster than the several thousandths of a second Frisch had estimated for slow-neutron fission.1268 Then how destructive was the consequent explosion? Some eighty generations of neutrons—as many as could be expected to multiply before the swelling explosion separated the atoms of U235 enough to stop the chain reaction—still millionths of a second in total, gave temperatures as hot as the interior of the sun, pressures greater than the center of the earth where iron flows as a liquid. “I worked out the results of what such a nuclear explosion would be,” says Peierls. “Both Frisch and I were staggered by them.”1269