Richard Brooke RobertsBorn 7 Dec 1910; died 4 Apr 1980 at age 69.American biophysicist who contributed most to the discovery of "delayed neutrons" - that uranium fission does not release all the neutrons it produces at one time, but some come off at measurably later times. Some are emitted seconds to minutes later. This is crucial in the operation of a fission reactor. In uranium-235 fission in a thermal reactor, the proportion of delayed neutrons is about 0.65 percent. If the reactivity stays below the proportion of delayed neutrons, the reactor can be controlled. The delayed neutrons modify the rate of fission sufficiently to give time for the insertion of control rods. Without the margin of safety provided by the delayed neutrons, nuclear reactors might not be practical at all.* |
