10 research outputs found
Evapotranspiração real de uma cultura de laranja em produção num Latossolo Vermelho-Amarelo
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Plutonium and americium in Lake Michigan sediments
The vertical distributions of ,Pu, Pu, and Cs have been measured in sediment cores taken from Lake Michigan. Sections from a limited number of cores have been analyzed for Am. In addition, grab samples from ten locations in the southern basin of the lake have been analyzed for phase distribution of ,Pu using a sequential extraction technique. The results indicate that the ,Pu, Pu, and Cs from weapons testing, and the Am formed in situ are concentrated in the sediments. A comparison of the total deposition of ,Pu and Cs indicates that Cs may be valuable as a monitor for ,Pu deposition in the sediments. Values of the Pu/,Pu ratio are in agreement with values reported in Lake Ontario sediments (and Lake Michigan plankton) and show little variation with depth. Am data support the concept of in situ production with little preferential mobility after formation. Studies of sedimentary phase distributions show that ,Pu is associated with hydrous oxide phases which are chemically stable under the prevailing conditions in lake sediments. Since Lake Michigan sediments remain aerobic, relatively little ,Pu is available for chemical mobilization from the hydrous oxide or organic phases present in the sediments. (auth