Implosion Mechanism for Plutonium Bomb
Nuclear weapons using plutonium-239 (an alternative to uranium-235) are triggered by an implosion mechanism, in which a spherical assembly of conventional high explosives compresses a subcritical core of a plutonium compound to supercritical density. A number of famous scientists working at Los Alamos, including Richard Tolman, John von Neumann, and Edward Teller contributed to this design. The first such device was successfully exploded near Alamogordo, NM in 1945, in a location now known as the Trinity Site. This Demonstration gives a highly simplified account of the implosion mechanism. (Some details are still classified.) It is important that the implosion geometry must be spherically symmetrical to high accuracy, otherwise ineffective preignition can occur. One design is based on a spherical array of 32 explosive charges.
Snapshot 1: initial configuration of bomb; explosive charges are shown in red, plutonium core in blue
Snapshot 2: just after ignition
Snapshot 3: the plutonium core is compressed to supercritical density
Snapshot 4: the resulting nuclear explosion
For more information, see the Wikipedia entry for Nuclear weapon design.