Uranium activity ratios

Figure 4 Measurements of (A) uranium activity ratios, UARs (234U 238U) and U concentrations (B) across a salinity gradient off the Amazon River mouth (1996). UARs were determined by thermal ionization mass spectrometry (TIMS) at Caltech (D. Porcelli) U concentrations by ICPMS...

Figure 4 Measurements of (A) uranium activity ratios, 1.22 Amazon River A...

The uranium activity ratio in water and fish samples from pit lakes in Kazakhstan and Tajikistan was determined by ICPMS, alpha spectrometry, and radiochemical neutron activation analysis (RNAA) (Stromman et al. 2013). The samples were collected from lakes that were formed in open pits in abandoned uranium mines. Fish in those lakes are occasionally consumed by the local population and domestic animals drink water from those lakes that contain high uranium levels (1 and 3 mg L ). The activity ratio was found to increase from about 1 to 1.5 a few kilome-... 

Stromman, G., Rosseland, B.O., Skipperud, L. et al. (2013). Uranium activity ratio in water and fish from pit lakes in Kurday, Kazakhstan and Taboshar, Tajikistan, J. Environ. Radioact. 123,71-81. 

Owing to the stability of the uranyl carbonate complex, uranium is universally present in seawater at an average concentration of ca. 3.2/rgL with a daughter/parent activity ratio U) of 1.14. " In particulate matter and bottom sediments that are roughly 1 x 10 " years old, the ratio should approach unity (secular equilibrium). The principal source of dissolved uranium to the ocean is from physicochemical weathering on the continents and subsequent transport by rivers. Potentially significant oceanic U sinks include anoxic basins, organic rich sediments, phosphorites and oceanic basalts, metalliferous sediments, carbonate sediments, and saltwater marshes. " ... 

Yanase N, Payne TE, Sekine K (1995) Groundwater geochemistry in the Koongarra ore deposit, Australia 2. Activity ratios and migration mechanisms of uranium series nuclides. Geochem J 29 31-54... 

Plater AJ, Ivanovich M, Dugdale RE (1995) Ra contents and Ra/ Ra activity ratios of the Fenland rivers and the Wash, eastern England spatial and seasonal trends. Chem Geol 119 275-292 Pliler R, Adams JAS (1962) The distribution of thorium and uranium in a Pennsylvanian weathering profile. Geochim Cosmochim Acta 26 1137-1146... 

Measuring the isotopic composition of U in estuaries has the potential for further constraining the interpretations of uranium behavior. However, this has been hampered by large uncertainties in conventional methods using counting techniques. While rivers often display ( " U/ U) activity ratios above equilibrium, the ratios generally do not... 

Owing to the stability of the uranyl carbonate complex, uranium is universally present in seawater at an average concentration of ca. 3.2/rgL with a daughter/parent activity ratio of 1.14. " In particulate matter and... 

Gladney ES, Peters RJ, Perrin DR. 1983. Determination of uranium- 235/uranium-238 ratio in natural waters by Chelex-100 ion exchange and neutron-activation analysis. Anal Chem 55 976-977. 

Andrews J. N. and Kay R. F. F. (1983) The U content and 234u/238u activity ratios of dissolved uranium in ground-waters from some Triassic sandstones in England. Isot. Geosci. 1, 101-117. 

Hakam O. K., Choukri A., Reyss J. L., and Lferde M. (2001) Determination and comparison of uranium and radium isotopes activities and activity ratios in samples from some natural water sources in Morocco. J. Environ. Radioact. 57, 175-189. 

Plater A. J., Ivanovich M., and Dugdale R. E. (1992) Uranium series disequihbrium in river sediments and waters the significance of anomalous activity ratios. Appl. Geochem. 7, 101-110. 

Equations (10) and (11) assume that initial Th and Pa concentrations are zero or can be corrected for. The Th/ U ratio in surface corals is similar to that in seawater, suggesting that thorium does not fractionate from uranium significantly during coral growth (Edwards et al., 1986-1987). Because of the extremely low Th/ U ratio in seawater (activity ratio —10 ), initial Th must be negligible. Concordance between Th and Pa ages indicates that initial Pa must also be negligible (Edwards et al., 1997). 

At equilibrium, the activity ratio between any two members of a decay series is 1.00. However, at and near the Earth s surface, disequilibrium of the various nuclides of the uranium series is found to occur. The disequilibrium is especially pronounced in groundwaters (Cherdyntsev, 1971 Osmond and Cowart, 1976). The fractionation of the nuclides can occur as a result of chemical differences between elements, the fractionation of isotopes of a given element may occur because of preferential leaching of one (because of its radiogenic origin), or by the direct action of recoil during radioactive decay (Osmond and Cowart, 1976). 

Site No. Location Uranium concentration 234u/238u activity ratio 2 Ra concentration (pCi/1)... 

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