A nuclear weapon is a weapon of enormous destructive potential, deriving its energy from nuclear fission or nuclear fusion reactions.

These weapons were initially developed in the United States during World War II in the Manhattan Project. A considerable amount of international negotiating has focused on the threat of nuclear warfare and the proliferation of nuclear weapons to new nations or groups.

This article discusses the historical development of nuclear weapons. Related articles include: nuclear weapons, nuclear weapon design, nuclear explosion, nuclear warfare, nuclear proliferation, nuclear strategy, nuclear reactor, Manhattan Project, Los Alamos National Laboratory

Contents

1 Development 2 World War II 3 Cold War 4 Hydrogen bomb 5 Other countries with nuclear weapons 6 Nuclear test explosions 7 See also 8 References 9 External links

Development

In 1905 Albert Einstein published his special theory of relativity. According to this theory, the relation between mass and energy is expressed by the equation E = mc², which states that a given mass (m) is associated with an amount of energy (E) equal to this mass multiplied by the square of the speed of light (c). A very small amount of matter is equivalent to a vast amount of energy.

In 1932 the neutron particle was discovered by James Chadwick.

In 1938 German chemists Otto Hahn and Fritz Strassmann were able to split the uranium atom into two roughly equal parts by bombarding it with neutrons. As a result of these experiments, the Austrian physicist Lise Meitner, with her nephew, the British physicist Otto Robert Frisch, were able to explain the process of nuclear fission in 1939, placing the release of atomic energy within reach.

World War II

Thus, the potential of nuclear reactions to be used for weapons of extremely high destructive power was known by the time World War II broke out. The leaders of the Allied nations were particularly concerned about Germany producing such weapons, and so began the Manhattan Project which brought the top minds in nuclear physics together, led by Robert Oppenheimer, under the U.S. military direction of Brigadier General Leslie Groves, with the goal of producing fission-based explosive devices. Britain and the U.S. agreed to pool their resources and information for the project, but the Soviet Union was not informed.

A massive industrial and scientific undertaking, Manhattan involved many of the world's great physicists in the scientific and development aspects. The work was centered around the laboratories at Los Alamos, New Mexico. As part of the project, the world's first sustained and controlled nuclear chain reaction was achieved at the University of Chicago under the supervision of Enrico Fermi. Apart from Chicago and Los Alamos, the Hanford Site in the state of Washington and Oak Ridge were the sites of large-scale production and purification of fissionable material.

The Manhattan Project was unable to produce fission-based weapons prior to the unconditional surrender of Germany on May 8, 1945, but was able to produce a test device (exploded at the Trinity site) and two deliverable devices, one using uranium 235 as fissionable material (known as Little Boy) and another using plutonium as fissionable material (known as Fat Man).

The 1945 Potsdam Declaration called for unconditional surrender by Japan; the Japanese, however, wanting a guarantee that their emperor would remain on the throne before they would surrender, continued fighting. Facing the prospects of a long, bloody, grueling "island-hopping" campaign to conquer Japan (and also wishing to intimidate the Soviet Union), U.S. President Harry Truman chose to enforce Japanese surrender by using the newly developed nuclear weapons. Little Boy was thus delivered to the Japanese city of Hiroshima by the bomber Enola Gay, and Fat Man by Bockscar to Nagasaki. These two bombings are still the only instances when atomic weapons were used in warfare. Ironically, after the Japanese did surrender, they were allowed to retain their emperor as a symbol.

Nazi Germany had also attempted to develop nuclear weapons, but erroneously concluded that slow neutron fission could not cascade fast enough to cause an explosion. Their physicists working on nuclear energy, lead by Werner Heisenberg, may have deliberately refused to notice fast neutron fission. Germany attempted to develop power reactors, but its supplies of graphite were poisoned by boron, a neutron absorber injected by the boron electrodes then used to provide commercial graphite. As a result, the Nazi reactor program attempted to develop heavy water reactors and was hampered by supply and purity problems. Leó Szilárd, a Hungarian physicist trained as an industrial chemist, successfully prevented this problem with American reactors, which used highly-purified graphite.

Germany probably tried to assist Japan in producing a nuclear weapon: in May 1945, the U.S. captured a U-boat heading for Japan with uranium oxide containing a fifth of the total U-235 needed to make one bomb. However, documents discovered in 2001 indicate that Japanese scientists were years away from completing an atomic weapon. The captured German uranium may have contributed to what was needed for the U.S. bombs.

See also: Norwegian heavy water sabotage, Atomic bombings of Hiroshima and Nagasaki

Cold War

On August 29, 1949, the Soviet Union detonates its first atomic device, ending the United States monopoly on nuclear weapons.

It is now known that the Soviet Union was able to develop nuclear weapons in relatively short time in part because of its espionage activities in the United States and the United Kingdom. Prime Minister Winston Churchill announced on February 26, 1952, that the United Kingdom also had an atomic bomb (which itself was not a surprising revelation, considering how many UK scientists worked at very high levels in the Manhattan Project). France and the People's Republic of China also demonstrated nuclear capability, and these five countries were considered to be the 'Nuclear Powers' throughout the Cold War period.

After World War II, the balance of power between the Eastern and Western blocs, resulting in the fear of global destruction, prevented the further military use of atomic bombs. This fear was even a central part of Cold War strategy, referred to as the doctrine of Mutually Assured Destruction ("MAD" for short). So important was this balance to international political stability that a treaty, the Antiballistic Missile Treaty (or ABM treaty) was signed by the U.S. and the USSR in 1972 to curtail the development of defenses against nuclear weapons and the ballistic missiles which carry them. This doctrine resulting in a large increase in the number of nuclear weapons, as each side sought to ensure it possessed the firepower to destroy the opposition in all possible scenarios and against all perceived threats.

Early delivery systems for nuclear devices were primarily bombers like the American B-29 Superfortress and B-36 Peacemaker, and later the B-52 Stratofortress. Ballistic missile systems, based on designs used by Germany under Wernher von Braun (specifically the V2 rocket), were developed by both American and Soviet teams (in the case of U.S., effort was directed by the captured German scientists and engineers). These systems, after testing, were used to launch satellites, such as Sputnik, and to propel the Space Race, but they were primarily developed to create the capability of Intercontinental Ballistic Missiles (ICBMs) with which nuclear powers could deliver that destructive force anywhere on the globe. These systems continued to be developed throughout the Cold War, although plans and treaties, beginning with the Strategic Arms Limitation Treaty (SALT I), restricted deployment of these systems until, after the fall of the Soviet Union, system development essentially halted, and many weapons were disabled and destroyed (see nuclear disarmament).

There have been a number of potential nuclear disasters. Following air accidents U.S. nuclear weapons have been lost near Atlantic City, New Jersey (1957), Savannah, Georgia (1958) (see Tybee Bomb), Goldsboro, North Carolina (1961), off the coast of Okinawa (1965), in the sea near Palomares , Spain (1966) and near Thule, Greenland (1968). Most of the lost weapons were recovered, the Spanish device after three months' effort by the DSV Alvin and DSV Aluminaut . The Soviet Union was less forthcoming about such incidents, but the environmental group Greenpeace believes that there are around forty non-U.S. nuclear devices that have been lost and not recovered, compared to eleven lost by America, mostly in submarine disasters. The U.S. have tried to recover Soviet devices, notably in the 1974 Operation Jennifer using the specialist salvage vessel Hughes Glomar Explorer.

On January 27, 1967, more than 60 nations signed the Outer Space Treaty banning nuclear weapons in space.

The end of the Cold War failed to bring an end to the threat of the use of nuclear weapons, although global fears of nuclear war reduced substantially.

In a major move of deescalation, Boris Yeltsin on January 26, 1992 announced that Russia planned to stop targeting United States cities with nuclear weapons.

Hydrogen bomb

The notion of using a fission weapon to ignite a process of nuclear fusion can be dated back to 1942. At the first major theoretical conference on the development of an atomic bomb hosted by J. Robert Oppenheimer at the University of California, Berkeley, participant Edward Teller directed the majority of the discussion towards Enrico Fermi's idea of a "Super" bomb. It was thought at the time that a fission weapon would be quite simple to develop and that perhaps work on a hydrogen bomb would be possible to complete before the end of the second World War. However in reality the problem of a "regular" atomic bomb was large enough to preoccupy the scientists for the next few years, much less the more speculative "Super." Only Teller continued working on the project -- against the will of project leaders Oppenheimer and Hans Bethe.

After the atomic bombings of Japan, many scientists at Los Alamos repelled against the notion of creating a weapon thousands of times more powerful than the first atomic bombs. For the scientists the question was in part technical -- the weapon design was still quite uncertain and unworkable -- and in part moral -- such a weapon, they argued, could only be used against large civilian populations, and could thus only be used as a weapon of genocide. Many scientists, such as Oppenheimer and Bethe, urged that the United States should not develop such weapons and set an example towards the Soviet Union. Promoters of the weapon, including Teller, Ernest Lawrence, and Luis Alvarez, argued that such a development was inevitable, and to deny such protection to the people of the United States -- especially when the Soviet Union was likely to create such a weapon themselves -- was itself an immoral and unwise act.

In the end, President Truman made the final decision, looking for a proper response to the first Soviet atomic bomb testing in 1949. On January 31, 1950, Truman announced a crash program to develop the hydrogen (fusion) bomb. At this point, however, the exact mechanism was still not known: the "classical" hydrogen bomb, whereby the heat of the fission bomb would be used to ignite the fusion material, seemed highly unworkable. However due to an insight by Los Alamos mathematician Stanislaw Ulam, that the radiation of the fission bomb could first compress the fusion material before igniting it. Teller pushed the notion further, and used the results of the boosted-fission "George" test (a boosted-fission device used a small amount of fusion fuel to boost the yield of a to confirm the fusion of heavy hydrogen elements before preparing for their first true multi-stage, Teller-Ulam hydrogen bomb test. Many scientists initially against the weapon, such as Oppenheimer and Bethe, changed their previous opinions, seeing the development as being unstoppable.

The first fusion bomb was tested by the United States in Operation Ivy on November 1, 1952, on Elugelab Island in the Enewetak (or Eniwetok) Atoll of the Marshall Islands, code-named Mike. It yielded 10.4 megatons of explosive power (equal to 10.4 million tons of TNT), which is over 450 times the power of the bomb that fell on Nagasaki. Mike used liquid deuterium as the fusion fuel and had a 92 point ignition system. It was 20 ft (6 m) high, 6 ft 8 in (2 m) wide, and weighing 140,000 lb (64 t) or 164,000 lb (74 t) including attached refrigeration and measuring equipment. The detonation obliterated Elugelab, leaving an underwater crater 6240 ft (1.9 km) wide and 164 ft (50 m) deep where the island had once been. Truman had initially tried to create a media blackout about the test -- hoping it would not become an issue in the upcoming presidential election -- but on January 7, 1953, Truman announced the development of the hydrogen bomb to the world.

The Soviet Union exploded its first thermonuclear device on August 12, 1953. This created concern within the U.S. government and military, because, unlike "Mike," the Soviet device was a deliverable weapon, which the U.S. did not yet have (however the 1953 Soviet bomb was arguably not a "true" hydrogen bomb in that it was not a multi-stage weapon). By 1954, though, the United States had detonated the "Shrimp" device during the Castle Bravo test, marking the first deployable hydrogen bomb. The device yielded almost twice as much power as was expected, and contaminated island natives and a Japanese fishing boat with deadly nuclear fallout. The Soviet Union detonated its first "true" hydrogen bomb in 1955.

Other thermonuclear devices were exploded by the United Kingdom on May 15, 1957, (Operation Grapple, test off Malden Island), France (February 13, 1960), and the People's Republic of China (October 16, 1964 - a nuclear device, June 14, 1967 - a hydrogen bomb). India claims to have exploded a thermonuclear device in 1998, though some (non-Indian) experts are unsure of whether it was a true hydrogen bomb or simply a boosted-fission device.

Other countries with nuclear weapons

France made a point of conducting above-ground tests of nuclear weapons in the 1990s.

India's first test atomic explosion was in 1974 with Smiling Buddha, which it initially described as a 'peaceful nuclear explosion'. India tested fission and perhaps fusion devices in 1998 and Pakistan successfully tested fission devices that same year, raising concerns that they would use nuclear weapons on each other. All of the former Soviet bloc countries with nuclear weapons (Belarus, Ukraine, and Kazakhstan) returned their warheads to Russia by 1996, though recent data has suggested that a clerical error may have left some warheads in the Ukraine.

In January 2004, Pakistani metallurgist and weapons scientist Abdul Qadeer Khan confessed to having been a part of an international proliferation network of materials, knowledge, and machines from Pakistan to Libya, Iran, and North Korea.

South Africa also had an active program to develop uranium based nuclear weapons, but dismantled its nuclear weapon program in the 1990s. It is not believed that it actually tested such a weapon. In the late 1970s American spy satellites detected what appeared to be a flash of gamma rays, but a later scientific review of the data suggested it may have been caused by natural events.

Israel is widely believed to possess an arsenal of potentially up to several hundred nuclear warheads, but this has never been officially confirmed or denied (though the existence of their Dimona nuclear facility was more or less confirmed by the leaks of dissident Mordechai Vanunu in 1986).

The United Kingdom has not run an independent development program since the failure of Blue Streak missile in the 1960s, buying American delivery systems and fitting British warheads instead (Polaris Sales Agreement).

The People's Republic of China possesses an arsenal of nuclear warheads estimated to be around 400 strong (in 2002). In 2003, North Korea announced it also had several nuclear explosives though it has not been confirmed and the validity of this has been a subject of scrutiny amongst weapons experts.

Nuclear test explosions

There have been around 2,000 nuclear explosions:

• United States: 1,030 tests (involving 1,125 devices)
• Soviet Union: 715 tests
• France: 210 tests
• United Kingdom: 45 tests (21 in Australian territory, including 9 in mainland South Australia at Maralinga and Emu Field)
• People's Republic of China: 45 tests (23 atmospheric and 22 underground, all conducted at Lop Nur Nuclear Weapons Test Base, in Malan , Xinjiang)
• India: 6 tests.
• Pakistan: 6 tests.

Australian government database of nuclear explosions and tests

See also

• Manhattan Project
• Los Alamos National Laboratory
• Nuclear explosion
• Nuclear test explosion
• Nuclear weapon
• Nuclear weapon design
• Nuclear warfare
• Nuclear arms race
• Nuclear proliferation
• List of nuclear accidents

References

• Rhodes, Richard. Dark Sun: The Making of the Hydrogen Bomb. Simon and Schuster, New York, 1995.
• Rhodes, Richard. The Making of the Atomic Bomb. Simon and Schuster, New York, 1986.

External links

• Timeline of atomic age events
• Nuclear History Documents from the National Security Archive
• Federation of American Scientists - Worldwide Nuclear Forces Guide
• Nuclear Weapons Archive - includes many country's nuclear weapon histories