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Preparation for an underground nuclear test at the Nevada Test Site in the 1980s. Visible in the photograph are the test monitoring equipment, as well as the subsidence craters created by previous underground nuclear tests.

Nuclear testing is experimentation with nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have staged tests of them. Testing nuclear weapons can yield information about how the weapons work, as well as how the weapons behave under various conditions and how structures behave when subjected to nuclear explosions. Additionally, nuclear testing has often been used as an indicator of scientific and military strength, and many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status by means of a nuclear test.

The first atomic test was detonated by the United States at the Trinity site on July 16, 1945, with a yield approximately equivalent to 20 kilotons. The first hydrogen bomb, codenamed "Mike", was tested at the Enewetak atoll in the Marshall Islands on November 1, 1952, 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 an estimated yield of around 50 megatons.

In 1963, all nuclear and many non-nuclear states signed the Limited Test Ban Treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. The treaty permitted underground tests. France continued atmospheric testing until 1974, while China continued up until 1980. The last underground test by the United States was in 1992, the Soviet Union in 1990, the United Kingdom in 1991, and both France and China continued testing up until 1996. After adopting the Comprehensive Test Ban Treaty in 1996, all of these states have pledged to discontinue all nuclear testing. Non-signatories India and Pakistan both last tested nuclear weapons in 1998.

The most recent nuclear test was announced by North Korea on October 9, 2006. See 2006 North Korean nuclear test for more information.

Types of nuclear testing

Nuclear weapons tests have been historically broken into categories (by treaties) reflecting in what sort of medium or location the test has been conducted: atmospheric, underwater, and underground.

Atmospheric testing designates explosions which take place in or above the atmosphere. Generally these have occurred as devices detonated on towers, balloons, barges, islands, or dropped from airplanes. A limited number of high-altitude nuclear explosions have also been conducted, generally fired from rockets. Nuclear explosions which are close enough to the ground to draw dirt and debris into their mushroom cloud can generate large amounts of nuclear fallout due to irradiation of the debris. High-altitude nuclear tests can generate an electromagnetic pulse, and charged particles resulting from the blast can cross hemispheres to create an auroral display.

Four major types of nuclear testing: 1. atmospheric, 2. underground, 3. exoatmospheric, and 4. underwater.

Underwater testing results from nuclear devices being detonated underwater, usually moored to a ship or a barge (which is subsequently destroyed by the explosion). Tests of this nature have usually been conducted to evaluate the effects of nuclear weapons against naval vessels (such as in Operation Crossroads), or to evaluate potential sea-based nuclear weapons (such as nuclear torpedoes or depth-charges). Underwater tests close to the surface can disperse large amounts of radioactive water and steam, contaminating nearby ships or structures.

Underground testing refers to nuclear tests which are conducted under the surface of the earth, at varying depths. Underground nuclear testing made up the majority of nuclear tests by the United States and the Soviet Union during the Cold War, on account of other forms of nuclear testing being banned by the Limited Test Ban Treaty in 1963. When the explosion is fully contained, underground nuclear testing emits a negligible amount of fallout. However, underground nuclear tests can "vent" to the surface, producing considerable amounts of radioactive debris as a consequence. Underground testing can result in seismic activity depending on the yield of the nuclear device, and generally result in the creation of subsidence craters. In 1976, the United States and the USSR agreed to limit the maximum yield of underground tests to 150 kt with the Threshold Test Ban Treaty.

Separately from these designations, nuclear tests are also often categorized by the purpose of the test itself. Tests which are designed to garner information about how (and if) the weapons themselves work are weapons related tests, while tests designed to gain information about the effects of the weapons themselves on structures or organisms are known as weapons effects tests. Additional types of nuclear tests are possible as well (such as nuclear tests which are also part of anti-ballistic missile testing).

Nuclear-weapons-related testing which purposely results in no yield is known as subcritical testing, referring to the lack of a creation of a critical mass of fissile material. Additionally, there have been non-nuclear simulations of nuclear tests using conventional explosives (such as the Minor Scale U.S. test in 1985).

History

The first nuclear test, "Trinity", took place on July 16, 1945.

The first nuclear test was conducted by the United States on July 16, 1945, during the Manhattan Project, and given the codename "Trinity". The test was originally to confirm that the implosion-type nuclear weapon design was feasible, and to give the scientists and military officers an idea of what the actual size and effects of a nuclear explosion would be before they were used in combat against Japan. While the test gave a good approximation of many of the explosion's effects, it did not give an appreciable understanding of nuclear fallout, which was not well understood by the project scientists until well after the atomic bombings of Hiroshima and Nagasaki.

The United States conducted only six nuclear tests before the Soviet Union developed their first atomic bomb (Joe 1) and tested it on August 29, 1949. Neither country had very many nuclear weapons to spare at first, and so testing was relatively limited (when the U.S. used two weapons for Operation Crossroads in 1946, they were detonating over 20% of their current arsenal). However, by the 1950s the United States had established a dedicated test site on its own territory (Nevada Test Site) and were also using a site in the Marshall Islands (Pacific Proving Grounds) for extensive nuclear testing.

The early tests were used primarily to discern the military effects of nuclear weapons (Crossroads had involved the effect of nuclear weapons on a navy, and how they functioned underwater) and to test new weapon designs. During the 1950s these included new hydrogen bomb designs, which were tested in the Pacific, and also new and improved fission weapon designs. The Soviet Union also began testing on a limited scale, primarily in Kazakhstan. During the later phases of the Cold War, though, both countries developed accelerated testing programs, testing many hundreds of bombs over the last half of the twentieth century.

The Castle Bravo explosion spread nuclear fallout for over a hundred miles of ocean, including inhabited islands, in 1954.

Nuclear tests can involve many hazards. A number of these were best illustrated in the U.S. Castle Bravo test in 1954. The weapon design tested was a new form of hydrogen bomb, and the scientists underestimated how vigorously some of the weapon materials would react. As a result, the explosion — with a yield of 15 Mt — was over twice what was predicted. Aside from this problem, the weapon also generated a large amount of radioactive nuclear fallout, more than had been anticipated, and a change in the weather pattern caused the fallout to be spread in a direction which had not been cleared ahead of time. The fallout plume spread high levels of radiation for over a hundred miles, contaminating a number of populated islands in nearby atoll formations (though they were soon evacuated, many of the islands' inhabitants suffered from radiation burns and later from other effects such as increased cancer rate and birth defects), as well as a Japanese fishing boat (Daigo Fukuryū Maru). One member of the boat's crew died from radiation sickness after returning to port, and it was feared that the radioactive fish they had been carrying had made it into the Japanese food supply.

Because of concerns about worldwide fallout levels, the Partial Test Ban Treaty was signed in 1963. Above are the per capita thyroid doses (in rads) in the continental United States resulting from all exposure routes from all atmospheric nuclear tests conducted at the Nevada Test Site from 1951-1962.

Bravo was the worst U.S. nuclear accident, but many of its component problems — unpredictably large yields, changing weather patterns, unexpected fallout contamination of populations and the food supply — occurred during other atmospheric nuclear weapons tests by other countries as well. Concerns over worldwide fallout rates eventually lead to the Partial Test Ban Treaty in 1963, which limited signatories to only underground testing. Not all atmospheric tests stopped, however, but because the United States and the Soviet Union in particular stopped testing aboveground it cut the number of atmospheric tests down substantially, since around 86% of all nuclear tests were conducted by those two countries. France continued atmospheric testing until 1974, and People's Republic of China until 1980.

Almost all new nuclear powers have announced their possession of nuclear weapons with a nuclear test. The only acknowledged nuclear power which claims to have never conducted a test was South Africa (see Vela Incident), which has since claimed to have dismantled all of its weapons. The state of Israel is widely thought by intelligence agencies to possess a sizeable nuclear arsenal, though it has never tested. Experts disagree on whether states can have reliable nuclear arsenals — especially ones using advanced warhead designs, such as hydrogen bombs and miniaturized weapons — without testing, though all agree that it is very unlikely to develop significant nuclear innovations without testing. One other approach is to use supercomputers to conduct "virtual" testing, but the value of these simulations without actual test result data is thought to be slim.

The Sedan test of 1962 was an experiment by the United States in using nuclear weapons to excavate large amounts of earth.

Some nuclear testing has been for "peaceful" purposes. These so-called peaceful nuclear explosions were used to evaluate whether nuclear explosions could be used for non-military purposes such as digging canals and artificial harbors, or to stimulate oil and gas fields. In most cases the results were too radioactive for use, and the programs proved neither economically sound or politically favorable.

Nuclear testing has also been used for clearly political purposes. The most explicit example of this was the detonation of the largest nuclear bomb ever created, the 50 megaton Tsar Bomba (with a maximum yield of 150 Mt), by the Soviet Union in 1961. This weapon was too large to be practically used against an enemy target, and it is not thought that any were actually manufactured except the one which was detonated in the test. The weapon was used by the USSR as a show of Soviet strength and force, rather than to be developed as an actual weapon or for specifically scientific purposes.

There have been many attempts to limit the number and size of nuclear testing; the most far-reaching was the Comprehensive Test Ban Treaty of 1996, which was not ratified by the United States. Nuclear testing has since become a controversial issue in the United States, with a number of politicians saying that future testing might be necessary to maintain the aging warheads from the Cold War. Because nuclear testing is seen as furthering nuclear arms development, many are also opposed to future testing as an acceleration of the arms race.

Nuclear testing by country

→詳細は「List of nuclear tests」を参照

The nuclear powers have conducted at least 2,000 nuclear test explosions (numbers are approximated, as some test results have been disputed):

ファイル:Nuclear use locations world map1.png

Over 2,000 nuclear tests have been staged by the eight or so nuclear powers in over a dozen different sites around the world.

• United States: 1,054 tests by official count (involving at least 1,151 devices, 331 atmospheric tests), most at Nevada Test Site and the Pacific Proving Grounds in the Marshall Islands, with ten other tests taking place at various locations in the United States, including Alaska, Colorado, Mississippi, and New Mexico (see nuclear weapons and the United States for details).[1]
• Soviet Union: 715 tests (involving 969 devices) by official count [2], most at Semipalatinsk Test Site and Novaya Zemlya, and a few more at various sites in Russia, Kazakhstan, Turkmenistan, and Ukraine.
• United Kingdom: 45 tests (21 in Australian territory, including 9 in mainland South Australia at Maralinga and Emu Field, some at Christmas Island in the Pacific Ocean, plus many others in the U.S. as part of joint test series)
• France: 210 tests, mostly at Reggane and Ekker in Algeria, and Fangataufa and Moruroa in French Polynesia.
• China: 45 tests (23 atmospheric and 22 underground, all conducted at Lop Nur Nuclear Weapons Test Base, in Malan, Xinjiang)
• India: between 5 and 6 underground tests, at Pokhran.
• Pakistan: between 3 and 6 tests, at Chagai Hills.
• North Korea: 1 test at Hwadae-ri.

Additionally, there may have been at least three alleged/disputed/unacknowledged nuclear explosions (see list of alleged nuclear tests). Of these, the only one taken seriously as a possible nuclear test is the Vela Incident, a possible detection of a nuclear explosion in the Indian Ocean in 1979 hypothesized to be a joint Israeli/South African test.

From the first nuclear test in 1945 until tests by Pakistan in 1998, there was never a period of more than 22 months with no nuclear testing. June 1998 to October 2006, when North Korea reported a successful underground nuclear test, was the longest period since 1945 with no acknowledged nuclear tests.

Graph of nuclear testing (North Korea not yet shown).

See also

• List of states with nuclear weapons
• List of nuclear tests
• Category:Nuclear test sites
• Effects of nuclear explosions
• List of military nuclear accidents (including nuclear weapons accidents)
• History of nuclear weapons
• Nuclear weapons design
• Live fire exercise
• High altitude nuclear explosion
• Partial Test Ban Treaty
• Underwater explosion
• National Technical Means

References

History

• Gusterson, Hugh. Nuclear Rites: A Weapons Laboratory at the End of the Cold War. Berkeley, CA: University of California Press, 1996.
• Hacker, Barton C. Elements of Controversy: The Atomic Energy Commission and Radiation Safety in Nuclear Weapons Testing, 1947-1974. Berkeley, CA: University of California Press, 1994.
• Schwartz, Stephen I. Atomic Audit: The Costs and Consequences of U.S. Nuclear Weapons. Washington, D.C.: Brookings Institution Press, 1998.
• Weart, Spencer R. Nuclear Fear: A History of Images. Cambridge, MA: Harvard University Press, 1985.

External links

• http://www.downwinders.org "We're all Downwinders Now"
• Atomic Veterans History Project (United States)
• Australian government database of nuclear explosions and tests
• Oklahoma Geological Survey Nuclear Explosion Catalog lists 2,199 explosions by date, country, location, yield etc.
• Table of Known Nuclear Tests Worldwide, from NRDC
• Gallery of U.S. nuclear tests (with detailed descriptions of each test series)
• Gallery and short descriptions of UK nuclear tests
• Account of fallout from Nevada Test Site in 1955 (PDF)
• Soviet Nuclear Test Summary
• Marshall Islands Nuclear Claims Tribunal
• Nuclear Testing at Nuclear Files.org
• Film footage of nuclear artillery test
• What About Radiation on Bikini Atoll?
• Nevada Desert Experience Nevada Desert Experience
• Western States Legal Foundation Western States Legal Foundation
• The Nuclear Weapon Archive [3]

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