Atmospheric nuclear weapon tests

The major source of plutonium in natural waters is the atmospheric fallout from nuclear weapons tests. Fallout plutonium is ubiquitous in marine and freshwater environments of the world with higher concentrations in the northern hemisphere where the bulk of nuclear weapons testing occurred(3). Much of the research on the aquatic chemistry of plutonium takes place in marine and freshwater systems where only fallout is present. 

Atmospheric fallout from nuclear weapon tests and aquatic... 

Am released to the atmosphere will be associated with particles and will settle to earth or be washed from the air in precipitation (e.g., rain, snow). 241 Am from atmospheric nuclear weapons tests is injected into the stratosphere and may remain in the atmosphere for decades, traveling all around the world and only slowly settling to earth. 241 Am released in nuclear accidents, like Chernobyl, stays in the lower atmosphere where it can begin settling out near the site from which it is released. Larger particles will settle out more quickly and over a smaller area smaller particles may remain in the atmosphere for several months and travel far from where they are released. Precipitation scrubs particles out of the air more rapidly and deposits them in areas where the precipitation occurs. 

Exposure of the general population to 241 Am via air, water, soil, and food are generally very low these background levels are a result of fallout from past atmospheric nuclear weapons tests. Since 1973, 241Am air concentrations have been less than 1 aCi/m3 (0.037 pBq/m3) and are continuing to decline (Bennett 1979). Levels around nuclear power plants are indistinguishable from fallout background (EPRI 1981). 

Nuclear Weapons Testing Range, Maralinga, South Australia, site of 12 hydronuclear experiments at Taranaki in 1960, 1961, and 1963 (Vixen B Trials) in which 22.2 kg of plutonium was dispersed, having been ejected 2,500feet vertically into the atmosphere. Cooper etal. 1994... 

Again the atmospheric 14C/C ratio is an excellent example. Man-induced disturbances of the environmental system lead to changes in the 14C/C ratio which are of the order of magnitude of the natural fluctuations or even larger the emission of 14C-free C02 from fossil energy consumption leads to a decrease, and the emission of man-made 14C from nuclear weapons testing, to an increase of the atmospheric 14C/C ratio. 

During the industrial era man has influenced the atmospheric 14C/C ratio. By 1950 input of C02 from combustion of fossil fuel had led to a decrease in this ratio of about 2 percent. By 1963 due to nuclear weapon tests, however, the atmospheric 14C level in the northern hemisphere had increased by about 100 percent. The present excess is still v30 percent. There is also an input of 14C from nuclear power and reprocessing plants. 

There would be, however, a considerable discrepancy between the model-calculated dilution factor and the dilution factor required if the biospheric C02 input were of comparable size as the fossil C02 input as stated by biologists [43]. For a discussion of this question see also Oeschger et al., [39]. Thirdly, we calculate the 14C dilution corresponding to the CO increase. In 1950, before the nuclear weapon tests, the integrated C02 production amounted to about 10 percent of the preindustrial atmospheric C02 content. If there had been no exchange with other reservoirs, a decrease of the 14C/C ratio by 10 percent would have resulted. Tree-ring 14C measurements indicated, however, a decrease by only about 2 percent. Again we calculate the system dilution. In a first approximation 4 and s are set equal to one and we obtain... 

Table 2. Estimated yields of atmospheric nuclear weapon tests (From UNSCEAR 1982)...

Tihe atmosphere contains many radionuclides which result from nuclear weapons testing and from natural processes. The nuclear weapons-produced radionuclides include both fission products and activation products from the construction materials of the device. The natural radionuclides include the decay products of radon and thoron, the natural radionuclides in the airborne dust, and the cosmic-ray-produced radionuclides which result from spallation reactions in the atmosphere. Through the determination of the absolute and relative concentrations of this wide spectrum of radionuclides, it should be possible to define the rates of both the long term stratospheric processes and the shorter term tropospheric processes. At the beginning of 1962 a ground-level... 

Decrease of Bovine Cesium-137 Concentrations Following the Cessations of Atmospheric Nuclear Weapons Testing... 

This report concerns the changes in concentration of 137Cs in edible tissues of range cattle following the cessation of atmospheric nuclear weapons test series. 

This study encompasses two periods without extensive atmospheric contamination by nuclear weapons testing. An informal voluntary testing moratorium was observed from Oct. 31,1958 until Sept. 1,1961. A limited... 

The samples collected after cessation of atmospheric nuclear weapons tests in 1958 and 1963 were examined to ascertain the relative rate of decrease of soft-tissue cesium-137 (Table I). In view of the analysis of variance studies, each tissue and location were considered separately,... 

The half-period for decrease of muscle cesium-137 concentration in NTS animals after the cessation of atmospheric nuclear weapons testing in 1959 appears anomalous (Table I and Figure 2). In addition to being considerably greater (2.3 years) than the other half-periods found, its standard deviation was larger than the value. If one considers only the initial rate of decrease of radiocesium in these muscle samples, one finds a half-period of 0.9 year which is quite consistent with other data. Examination of these data, in comparison with data from liver (Figures 2 and 3), indicates that only muscle decreased its rate of decline in 1960. It should also be noted that the values during 1960 were only about twice the standard error of analysis. Thus, analytical error alone is not an improbable cause of these anomalous values. 

The three test herds were exposed to different mixtures of local and world-wide fallout. When atmospheric nuclear weapons testing ceases, animals in the NTS herd reach a greater maximum in soft-tissue 137Cs concentration faster than animals in the other two herds (5). This is because the DV and KC herds respond primarily to world-wide fallout which... 

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