Thermonuclear weapon in the context of "Castle Bravo"

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission (fission or atomic bomb) or a combination of fission and nuclear fusion reactions (thermonuclear weapon), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter.

Nuclear weapons have had yields between 10 tons (the W54) and 50 megatons for the Tsar Bomba (see TNT equivalent). Yields in the low kilotons can devastate cities. A thermonuclear weapon weighing as little as 600 pounds (270 kg) can release energy equal to more than 1.2 megatons of TNT (5.0 PJ). Apart from the blast, effects of nuclear weapons include extreme heat and ionizing radiation, firestorms, radioactive nuclear fallout, an electromagnetic pulse, and a radar blackout.

Nuclear weapons tests are experiments carried out to determine the performance of nuclear weapons and the effects of their explosion. Over 2,000 nuclear weapons tests have been carried out since 1945. Nuclear testing is a sensitive political issue. Governments have often performed tests to signal strength. Because of their destruction and fallout, testing has seen opposition by civilians as well as governments, with international bans having been agreed on. Thousands of tests have been performed, with most in the second half of the 20th century.

The first nuclear device was detonated as a test by the United States at the Trinity site in New Mexico on July 16, 1945, with a yield approximately equivalent to 20 kilotons of TNT. The first thermonuclear weapon technology test of an engineered device, codenamed Ivy Mike, was tested at the Enewetak Atoll in the Marshall Islands on November 1, 1952 (local date), also by the United States. The largest nuclear weapon ever tested was the Tsar Bomba of the Soviet Union at Novaya Zemlya on October 30, 1961, with the largest yield ever seen, an estimated 50–58 megatons.

The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated. It is usually expressed as a TNT equivalent, the standardized equivalent mass of trinitrotoluene (TNT) which would produce the same energy discharge if detonated, either in kilotonnes (symbol kt, thousands of tonnes of TNT), in megatonnes (Mt, millions of tonnes of TNT). It is also sometimes expressed in terajoules (TJ); an explosive yield of one terajoule is equal to 0.239 kilotonnes of TNT. Because the accuracy of any measurement of the energy released by TNT has always been problematic, the conventional definition is that one kilotonne of TNT is held simply to be equivalent to 10 calories.

The yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon. The practical maximum yield-to-weight ratio for fusion weapons (thermonuclear weapons) has been estimated to six megatonnes of TNT per tonne of bomb mass (25 TJ/kg). Yields of 5.2 megatonnes/tonne and higher have been reported for large weapons constructed for single-warhead use in the early 1960s. Since then, the smaller warheads needed to achieve the increased net damage efficiency (bomb damage/bomb mass) of multiple warhead systems have resulted in increases in the yield/mass ratio for single modern warheads.

The Tsar Bomba (code name: Ivan or Vanya, internal designation "AN602") was the most powerful nuclear weapon or weapon of any kind ever constructed and tested. A project of the Soviet Union, it was a thermonuclear aerial bomb, tested on 30 October 1961 at the Novaya Zemlya site in the country's far north. The bomb yielded 50 megatons of TNT.

The Soviet physicist Andrei Sakharov oversaw the project at Arzamas-16, while the main work of design was by Sakharov, Viktor Adamsky, Yuri Babayev, Yuri Smirnov [ru], and Yuri Trutnev. The project was ordered by First Secretary of the Communist Party Nikita Khrushchev in July 1961 as part of the Soviet resumption of nuclear testing after the Test Ban Moratorium, with the detonation timed to coincide with the 22nd Congress of the Communist Party of the Soviet Union (CPSU).

Nuclear fallout is residual radioisotope material that is created by the reactions producing a nuclear explosion or nuclear accident. In explosions, it is initially present in the radioactive cloud created by the explosion, and "falls out" of the cloud as it is moved by the atmosphere in the minutes, hours, and days after the explosion. The amount of fallout and its distribution is dependent on several factors, including the overall yield of the weapon, the fission yield of the weapon, the height of burst of the weapon, and meteorological conditions.

Fission weapons and many thermonuclear weapons use a large mass of fissionable fuel (such as uranium or plutonium), so their fallout is primarily fission products, and some unfissioned fuel. Cleaner thermonuclear weapons primarily produce fallout via neutron activation. Salted bombs, not widely developed, are tailored to produce and disperse specific radioisotopes selected for their half-life and radiation type.

Stanisław Marcin Ulam (Polish: [sta'ɲiswaf 'mart͡ɕin 'ulam]; 13 April 1909 – 13 May 1984) was a Polish and American mathematician, nuclear physicist and computer scientist. He participated in the Manhattan Project, originated the Teller–Ulam design of thermonuclear weapons, discovered the concept of the cellular automaton, invented the Monte Carlo method of computation, and suggested nuclear pulse propulsion. In pure and applied mathematics, he proved a number of theorems and proposed several conjectures.

Born into a wealthy Polish Jewish family in Lemberg, Austria-Hungary, Ulam studied mathematics at the Lwów Polytechnic Institute, where he earned his PhD in 1933 under the supervision of Kazimierz Kuratowski and Włodzimierz Stożek. In 1935, John von Neumann, whom Ulam had met in Warsaw, invited him to come to the Institute for Advanced Study in Princeton, New Jersey, for a few months. From 1936 to 1939, he spent summers in Poland and academic years at Harvard University in Cambridge, Massachusetts, where he worked to establish important results regarding ergodic theory. On 20 August 1939, he sailed for the United States for the last time with his 17-year-old brother Adam Ulam. He became an assistant professor at the University of Wisconsin–Madison in 1940, and a United States citizen in 1941.

A submarine-launched ballistic missile (SLBM) is a ballistic missile capable of being launched from submarines. Modern variants usually deliver multiple independently targetable reentry vehicles (MIRVs), each of which carries a nuclear warhead and allows a single launched missile to strike several targets. Submarine-launched ballistic missiles operate in a different way from submarine-launched cruise missiles.

Modern submarine-launched ballistic missiles are closely related to intercontinental ballistic missiles (ICBMs), with ranges of over 5,500 kilometres (3,000 nmi), and in many cases SLBMs and ICBMs may be part of the same family of weapons.

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

1. Pure fission weapons are the simplest, least technically demanding, were the first nuclear weapons built, and so far the only type ever used in warfare, by the United States on Japan in World War II.
2. Boosted fission weapons are fission weapons that use nuclear fusion reactions to generate high-energy neutrons that accelerate the fission chain reaction and increase its efficiency. Boosting can more than double the weapon's fission energy yield.
3. Staged thermonuclear weapons are arrangements of two or more "stages", most usually two, where the weapon derives a significant fraction of its energy from nuclear fusion (as well as, usually, nuclear fission). The first stage is typically a boosted fission weapon (except for the earliest thermonuclear weapons, which used a pure fission weapon). Its detonation causes it to shine intensely with X-rays, which illuminate and implode the second stage filled with fusion fuel. This initiates a sequence of events which results in a thermonuclear, or fusion, burn. This process affords potential yields hundreds or thousands of times greater than those of fission weapons.

Pure fission weapons 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.