Noun
predetonation (countable and uncountable, plural predetonations)
When a nuclear bomb fails to produce full yield, due to the chain reaction starting prematurely, before the system is at optimum criticality.
The plutonium-240 would start the chain reaction too quickly, causing a predetonation that would release enough energy to disperse the critical mass with a minimal amount of plutonium reacted (a fizzle ). Source: Internet
Predetonation If two pieces of subcritical material are not brought together fast enough, nuclear predetonation can occur, whereby a smaller explosion than expected will blow the bulk of the material apart. Source: Internet
To prevent predetonation by an external neutron, the tamper was coated in a thin layer of boron. Source: Internet