Nuclear Weapon

The largest modern weapons include a fissionable outer shell of uranium. The intense fast neutrons from the fusion stage of the weapon will cause even natural (that is unenriched) uranium to fission, increasing the yield of the weapon many times.

The cobalt bomb uses cobalt in the shell, and the fusion neutrons convert the cobalt into cobalt-60, a powerful long-term (5 years) emitter of gamma rays. In general this type of weapon is a salted bomb and variable fallout effects can be obtained by using different salting isotopes. Gold has been proposed for short-term fallout (days), tantalum and zinc for fallout of intermediate duration (months), and cobalt for long term contamination (years). The primary purpose of this weapon is to create extremely radioactive fallout making a large region uninhabitable. No cobalt or other salted bomb has been built or tested publicly.

A final variant of the thermonuclear weapons is the enhanced radiation weapon, or neutron bomb which are small thermonuclear weapons in which the burst of neutrons generated by the fusion reaction is intentionally not absorbed inside the weapon, but allowed to escape. The X-ray mirrors and shell of the weapon are made of chromium or nickel so that the neutrons are permitted to escape. This intense burst of high-energy neutrons is the principle destructive mechanism. Neutrons are more penetrating than other types of radiation so many shielding materials that work well against gamma rays are rendered less effective. The term "enhanced radiation" refers only to the burst of ionizing radiation released at the moment of detonation, not to any enhancement of residual radiation in fallout (as in the salted bombs discussed above).

For more technical details see: Nuclear weapon design

The dominant effects of a nuclear weapon (the blast and thermal radiation) are the same physical damage mechanisms as conventional explosives. The primary difference is that nuclear weapons are capable of releasing much larger amounts of energy at once. Most of the damage caused by a nuclear weapon is not directly related to the nuclear process of energy release, but would be present for any explosion of the same magnitude.

The damage done by each of the three initial forms of energy release differs with the size of the weapon. Thermal radiation drops off the slowest with distance, so the larger the weapon the more important this effect becomes. Ionizing radiation is strongly absorbed by air, so it is only dangerous by iteself for smaller weapons. Blast damage falls off more quickly than thermal radiation but more slowly than ionizing radiation.

When a nuclear weapon explodes, the bomb's material comes to an equilibrium temperature in about a microsecond. At this time about 75% of the energy is emitted as primary thermal radiation, mostly soft X-rays. Almost all of the rest of the energy is kinetic energy in rapidly-moving weapon debris. The interaction of the x-rays and debris with the surroundings determines how much energy is produced as blast and how much as light. In general, the denser the medium around the bomb, the more it will absorb, and the more powerful the shockwave will be.

In a burst at high altitudes, where the air density is low, the soft X rays travel long distances before they are absorbed. The energy is so diluted that the blast wave may be half as strong or less. The rest of the energy is dissipated as a more powerful thermal pulse.

Severe local fallout contamination can extend far beyond the blast and thermal effects, particularly in the case of high yield surface detonations. In detonations near a water surface, the particles tend to be lighter and smaller and produce less local fallout but will extend over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding affect causing local rainout and areas of high local fallout.

The radiobiological hazard of worldwide fallout is essentially a long-term one due to the potential accumulation of long-lived radioisotopes, such as strontium-90 and cesium-137, in the body as a result of ingestion of foods incorporating these radioactive materials. The hazard of worldwide fallout is much less serious than the hazards which are associated with local fallout.

Blast and thermal injuries in many cases will far outnumber radiation injuries. However, radiation effects are considerably more complex and varied than are blast or thermal effects and are subject to considerable misunderstanding. A wide range of biological changes may follow the irradiation of animals, ranging from rapid death following high doses of penetrating whole-body radiation to essentially normal lives for a variable period of time until the development of delayed radiation effects, in a portion of the exposed population, following low dose exposures.

For more technical details see: nuclear explosion

Nuclear weapons in culture

Nuclear weaponry has become a part of our culture, the decades post-WW II being can be termed the atomic age. The stunning power and the astonishing visual effects are a strong influence on art, from Andy Warhol's silkscreen Atomic Bomb (1965) and James Rosenquist's F-111 (1964-65) to Gregory Green's constructions and the efforts of artist James Acord to use uranium in his sculptures.

Films featuring nuclear war or the threat of it include Dr. Strangelove or, How I Learned to Stop Worrying and Love the Bomb, On The Beach, The Day After, The War Game (1966), Threads (1985), WarGames (1983); as well as less-famous films such as Miracle Mile and Broken Arrow (1996). Also the series of movies Planet of the Apes finish with the launching of cobalt bombs. Godzilla is considered by some to be an analogy to the nuclear weapons dropped on Japan.

A memorable episode of The Bionic Woman featured the threat of a cobalt bomb. A main character in Repo Man was a designer of the neutron bomb.

Nuclear weapons are a staple element in science fiction novels. The so-called dirty bomb was predicted in a 1943 article by Robert A. Heinlein titled "Solution Unsatisfactory" which caused him to be investigated by the FBI, concerned that there had been a breach of security on the Manhattan Project.

• More Technical Details
  • nuclear weapon design
  • nuclear explosion
• History
  • History of nuclear weapons
  • Manhattan Project
  • Los Alamos National Laboratory
  • Nuclear test explosion
• Related Technology and Science
  • nuclear physics
  • nuclear fission
  • nuclear fusion
  • nuclear reactor
  • nuclear engineering
• Military Strategy
  • nuclear warfare
  • nuclear strategy
  • Mutual Assured Destruction
• Proliferation and Politics
  • nuclear proliferation
  • Nuclear Non-Proliferation Treaty
  • Comprehensive Test Ban Treaty
  • nuclear disarmament
• General
  • Weapons of mass destruction

References

External links