Radioactive cesium isotope ratios as a tool for determining dispersal and re-dispersal mechanisms downwind from the Nevada Nuclear Security Site

• Published in: Journal of environmental radioactivity Vol. 110; pp. 46 - 52
• Main Authors: Snyder, Darin C., Delmore, James E., Tranter, Troy, Mann, Nick R., Abbott, Michael L., Olson, John E.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.08.2012; Elsevier
• Subjects: Applied sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; CESIUM; CESIUM ISOTOPES; Cesium Radioisotopes - analysis; Continental surface waters; DECAY; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Monitoring - methods; Exact sciences and technology; FRACTIONATION; GASES; IODINE; ISOTOPE RATIO; Isotope ratios; Lakes - chemistry; Natural water pollution; Nevada; Nevada Nuclear Security Site; Nevada Nuclear Security Site (NNSS); NUCLEAR FUEL CYCLE AND FUEL MATERIALS; PLUMES; Pollution; Pollution, environment geology; Radioactive cesium; Radioactive Cesium Isotope Ratios; SECURITY; Soil and sediments pollution; Tests; Water Pollutants, Chemical - analysis; Water treatment and pollution; XENON; United States; North America; America; Nevada; Nevada Nuclear Security Site; Radioactive cesium; Isotope ratios; Tests; Isotopic analysis; Cesium 137; Radioactive pollution; Atmospheric fallout; Pollutant behavior; Cesium 135; Plume; Radioisotope; Lake sediments; Nuclear weapon; Surface water; Lakes; Nuclear explosion; Air pollution; Water pollution
• ISSN: 0265-931X; 1879-1700
• DOI: 10.1016/j.jenvrad.2012.01.019

Fractionation of the two longer-lived radioactive cesium isotopes (135Cs and 137Cs) produced by above ground nuclear tests have been measured and used to clarify the dispersal mechanisms of cesium deposited in the area between the Nevada Nuclear Security Site and Lake Mead in the southwestern United States. Fractionation of these isotopes is due to the 135-decay chain requiring several days to completely decay to 135Cs, and the 137-decay chain less than one hour decay to 137Cs. Since the Cs precursors are gases, iodine and xenon, the 135Cs plume was deposited farther downwind than the 137Cs plume. Sediment core samples were obtained from the Las Vegas arm of Lake Mead, sub-sampled and analyzed for 135Cs/137Cs ratios by thermal ionization mass spectrometry. The layers proved to have nearly identical highly fractionated isotope ratios. This information is consistent with a model where the cesium was initially deposited onto the land area draining into Lake Mead and the composite from all of the above ground shots subsequently washed onto Lake Mead by high intensity rain and wind storms producing a layering of Cs activity, where each layer is a portion of the composite. ► We measure 135Cs/137Cs isotope ratios by mass spectrometry in environmental samples. ► Isotopic fraction between Cs isotopes is documented. ► Cs isotopic data are consistent with re-distribution of sediment around Lake Mead.