Nuclear Chain Reaction - Nuclear Weapons Application of Neutron Multiplication - Predetonation


Detonation of a nuclear weapon involves bringing fissile material into its optimal supercritical state very rapidly. During part of this process, the assembly is supercritical, but not yet in an optimal state for a chain reaction. Free neutrons, in particular from spontaneous fissions, can cause the device to undergo a preliminary chain reaction that destroys the fissile material before it is ready to produce a large explosion, which is known as predetonation. To keep the probability of predetonation low, the duration of the non-optimal assembly period is minimized and fissile and other materials are used which have low spontaneous fission rates. In fact, the combination of materials has to be such that it is unlikely that there is even a single spontaneous fission during the period of supercritical assembly. In particular, the gun method cannot be used with plutonium (see nuclear weapon design).

Read more about this topic:  Nuclear Chain Reaction, Nuclear Weapons Application of Neutron Multiplication

Other articles related to "predetonation":

Thin Man (nuclear Bomb) - Design Issues - Predetonation
... The distance required to accelerate the plutonium to speeds where predetonation would be less likely would need a gun barrel too long for any existing or planned bomber ...
Manhattan Project - Plutonium - Weapon Design
... 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) ... in armor-piercing shells, argued that not only would implosion reduce the danger of predetonation and fizzle, but would make more efficient use of the fissionable material ... To prevent predetonation by an external neutron, the tamper was coated in a thin layer of boron ...