Significant amounts of atmospheric testing of nuclear weapons took place from 1945 to 1980. The first nuclear weapons test, TRINITY, was conducted on a steel tower at Alamogordo in the south-central New Mexico on 16 July 1945. The nuclear explosion creates a radioactive cloud that usually takes the form of a huge mushroom. Explosion converts a small atomic mass into an enormous amount of energy through nuclear fission or fusion. Fission releases energy by splitting uranium or plutonium atoms into radioactive elements. Fusion, triggered by a fission explosion that forces tritium or deuterium atoms to combine into larger atoms, produces more powerful explosive yields than fission. The nuclear weapons test resulted in the release of substantial quantities of radioactive debris to the environment. The debris spread over large areas downwind of test sites, depending on the heights of bursts, the yields, and the meteorological conditions of temperature, precipitation, wind speed, and direction that vary with altitude. Usually, large particles settle locally, whereas small particles and gases may travel a long distance. There was evidence of long-range transport and fallout of debris from the test when the beta activity was first picked up by the film packaging material at mills of Kodak Research Laboratories in Indiana and Iowa in the summer of 1945. On the other hand, large atmospheric explosions may inject radioactive material into the stratosphere, 10 km or more above the ground, where it could remain in the atmosphere for years and subsequently be distributed globally and eventually deposited into the ground (i.e., global fallout) thereby contaminating the radioactivity level in the ecological environment.
After the TRINITY test, the Soviet Union conducted its first nuclear weapons test at a site near Semipalatinsk, Kazakhstan in 1949. The fallout from the series of detonations at the Nevada Test Site in 1951 had resulted in long-range transport of radioactive dust collected at the Eastman Kodak Company in Rochester, New York. The United States, the Soviet Union, and the United Kingdom continued nuclear weapons tests in the atmosphere until a limited test ban treaty was signed in 1963, except France and China. France undertook atmospheric testing from 1960 through 1974 and China from 1964 through 1980. Altogether, over 500 weapons tests were conducted in the atmosphere at a number of locations around the world, yielding the equivalent explosive power of 440 Mt of trinitrotoluene (TNT; i.e., 1 kt of TNT = 4.184 TJ energy released) which was estimated as 189 Mt of fission yield and 251 Mt of fusion yield, as shown in Figure 1. That is equivalent to 29 333 Hiroshima-size bombs, which was 15 kt of TNT on 6 August 1945. This would have been equivalent to exploding a Hiroshima-size bomb in the atmosphere every 11 h for the 36 years between 1945 and 1980. Clearly, significant amount of radionuclides
Figure 1 Fission and fusion yields for each year during nuclear weapons tests. From Beck H and Bennett BG (2002) Historical overview of atmospheric nuclear weapons testing and estimates of fallout in the continental United States. Health Physics 82: 591-608.
was dumped into the atmosphere in these 36 years. That would certainly increase the level of ambient radioactivity to cause extreme harm to the ecosystems.
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