Nuclear weapon design

Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package[1] of a nuclear weapon to detonate. There are three existing basic design types:

  • 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 warfare (by the United States on Japan during WWII).
  • 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 normally a boosted fission weapon as above (except for the earliest thermonuclear weapons, which used a pure fission weapon instead). 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.[2]
The first nuclear explosive devices, cumbersome and inefficient, provided the basic design building blocks of all future weapons. Pictured is the Gadget device being prepared for the first nuclear test, Trinity.

A fourth type, pure fusion weapons, are 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 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.

Most known innovations in nuclear weapon design originated in the United States, although some were later developed independently by other states.[3]

In early news accounts, pure fission weapons were called atomic bombs or A-bombs and weapons involving fusion were called hydrogen bombs or H-bombs. Practitioners, however, favor the terms nuclear and thermonuclear, respectively.


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