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; Shean P. Monahan; Norman L. Pruvost; Vladimir V. Frolov; Boris G. Ryazanov; 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, retrieved 16 April 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