| Popis: |
The gamma—emitting radionuclides derived from worldwide fallout were measured in samples of Arctic tundra vegetation collected from the Ogotoruk Valley, northwestern Alaska, during the summers of 1959, 1960, and 1961. Cerium—praseodymium—144 was the most abundant radionuclide measured during the 3 years of study. Smaller amounts of rutheniumrhodium—106, zirconium—niobium—95, cesium—137, manganese—54, and zinc—65 were also measured. Radioactivity of vegetation diminished from 1959 to 1961 primarily as a result of the decay of fallout radionuclides in the virtual absence of nuclear explosions in the earth's atmosphere. In 1961 the long—lived radionuclide cesium—137 contributed a larger percentage of total fallout radioactivity than it had in previous years. Lichens and mosses contained more radioactivity than their associated terrestrial vascular plants. Foliar interception appeared to be an important means of fallout accumulation. Terrestrial plants with persistent aboveground parts accumulated more cesium—137 than plants with more ephemeral aboveground parts. The lowest cesium—137 values were associated with aquatic emergent plants having aerially exposed parts for the shortest periods of time. |
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