Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package
[1] of a
nuclear weapon to detonate. There are three basic design types. In all three, the explosive energy is derived primarily from
nuclear fission, not
fusion.
Pure fission weapons are always the first type to be built by a nation state, and, if such a thing should happen, would be the type built by a non-state terrorist organization,[2]. Large industrial states with well-developed nuclear arsenals have two-stage thermonuclear weapons, which are the most compact, scalable, and cost effective option once the necessary industrial infrastructure is built.
All innovations in nuclear weapon design originated in the United States;[3] the following descriptions feature U.S. designs.
In early news accounts, pure fission weapons were called atomic bombs or A-bombs, a misnomer since the energy comes only from the nucleus of the atom. Weapons involving fusion were called hydrogen bombs or H-bombs, also a misnomer since their destructive energy comes mostly from fission. Insiders favored the terms nuclear and thermonuclear, respectively.
