prompt criticality

prompt criticality (usually uncountable, plural prompt criticalities)

1. (nuclear physics) The point at which the prompt neutrons produced by a nuclear fission chain reaction are just sufficient to sustain the chain reaction on their own (the state of being prompt critical); past this point, changes in reaction power are controlled by changes in the prompt neutron flux, and occur on a timeframe of milliseconds, too rapidly to be controlled by mechanical means.
   • 2000, Thomas P. McLaughlin with Shean P. Monahan, Norman L. Pruvost, Vladimir V. Frolov, Boris G. Ryazanov, and Victor I. Sviridov, “I. A. 19. Idaho Chemical Processing Plant, 17 October 1978”, in A Review of Criticality Accidents: 2000 Revision‎, Los Alamos National Laboratory, archived from the original on 25 March 2022, page 46:

     The system is thought to have approached prompt criticality, at which time the rate of power increase would have been determined by the neutron lifetime (on the order of milliseconds).

• delayed criticality