The nuclear tests conducted by the superpowers, especially in the years 1950-1960, were the source of radioactive releases into the environment and have caused, to date, the largest collective dose of uncontrolled radiation. The radioactive contamination still exists, although attenuated by time.
In total, throughout the Cold War and the race for atomic arms, 543 atmospheric tests were conducted. Most of them have been performed by the United States and the Soviet Union, the others by the United Kingdom, France and China.
Following the treaty signed in 1963 between the United States and the Soviet Union banning atmospheric tests, the two superpowers began an extensive program of underground tests until the early 1990s.
Underground tests are not the source of exposure far from the explosion point, at least in the absence of leak or release of radioactivity. Underground programs of France and China continued until 1996. India performed its first underground test in 1974, then five more in 1998, which Pakistan responded a few weeks later by conducting six tests.
Underground programs of France and China continued until 1996. India performed its first underground test in 1974, then five more in 1998, which Pakistan responded a few weeks later by conducting six tests.
Although there was an international consensus to ban all types of tests, the CTBT (Comprehensive Test Ban Treaty) issued in 1996, has not yet be fully applied. India, Pakistan, as well as Israel, have not yet ratified it, so that one cannot say that nuclear testing has finally ended. Iran is suspected of a military nuclear program. North Korea has detonated 3 bombs in 2006, 2009 and 2013. Since September 11th 2001, there is a concern about the use of dirty weapons by terrorist groups.
The total power generated by the atmospheric tests was of 440 megatons of TNT, these of underground tests: 90 megatons. The most active years were 1954, 1958, 1961 and 1962. The most powerful explosion is a thermonuclear (H-bomb) Soviet bomb of 50 megatons in 1961, including 97% due to fusion and 3% to fission. In comparison, the powers of the two bombs that destroyed Hiroshima and Nagasaki were much smaller: 15 and 21 kilotons.
The yields of most underground tests were lower than that of atmospheric tests and it was usually possible to contain the debris.
Americans detonated their tests on the atolls of the Marshall Islands in the Pacific and in the New Mexico and Nevada deserts. The most powerful and polluting thermonuclear test - the Casle Bravo - occurred in 1954 on the Bikini atoll with a yield of 15 megatons of TNT. Soviet sites are located in desert areas of Kazakhstan and Novaya Zemlya in the north of the Arctic Circle. The Soviets also made several unsuccessful attempts to use nuclear explosive for civil engineering. France conducted most of its underground tests on the atoll of Muruora.
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