Nuclear weapon design

Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types: A fourth type, pure fusion weapons, is a theoretical possibility. Such weapons would produce far fewer radioactive byproducts than current designs, although they would release huge numbers of neutrons.
 * pure fission weapons, the simplest and least technically demanding, were the first nuclear weapons built and have so far been the only type ever used in an act of war (over wartime Japan).
 * boosted fission weapons increase yield beyond that of the implosion design by using small quantities of fusion fuel to enhance the fission chain reaction. Boosting can more than double the weapon's fission energy yield.
 * staged thermonuclear weapons are essentially arrangements of two or more "stages", most usually two. The first stage is always a boosted fission weapon as above. Its detonation causes it to shine intensely with x-radiation, which illuminates and implodes the second stage filled with a large quantity of fusion fuel. This sets in motion a sequence of events which results in a thermonuclear, or fusion, burn. This process affords potential yields up to hundreds of times those of fission weapons.

Pure fission weapons historically have been the first type to be built by new nuclear powers. 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 technical base and industrial infrastructure are built.