Behavior Of Uranium Isotopes Research Articles

Activity disequilibrium between 234U and 238U isotopes in natural environment.

The aim of this work was to calculate the values of the 234U/238U activity ratio in natural environment (water, sediments, Baltic organisms and marine birds from various regions of the southern Baltic Sea; river waters (the Vistula and the Oder River); plants and soils collected near phosphogypsum waste heap in Wiślinka (Northern Poland) and deer-like animals from Northern Poland. On the basis of the studies it was found that the most important processes of uranium geochemical migration in the southern Baltic Sea ecosystem are the sedimentation of suspended material and the vertical diffusion from the sediments into the bottom water. Considerable values of the 234U/238U are characterized for the Vistula and Oder Rivers and its tributaries. The values of the 234U/238U activity ratio in different tissues and organs of the Baltic organisms, sea birds and wild deer are varied. Such a large variation value of obtained activity ratios indicates different behavior of uranium isotopes in the tissues and organisms of sea birds and wild animals. This value shows that uranium isotopes can be disposed at a slower or faster rate. The values of the 234U/238U activity ratio in the analyzed plants, soils and mosses collected in the vicinity of phosphogypsum dumps in Wiślinka are close to one and indicate the phosphogypsum origin of the analyzed nuclides. Uranium isotopes 234U and 238U are not present in radioactive equilibrium in the aquatic environment, which indicates that their activities are not equal. The inverse relationship is observed in the terrestrial environment, where the value of the of the 234U/238U activity ratio really oscillates around unity.

The behaviour of uranium isotopes with salinity change in three U.K. estuaries

The behaviour of natural uranium isotopes during estuarine mixing has been studied in three British estuaries. Uranium exhibits conservative behaviour in the Clyde and Tamar estuaries but there is evidence of removal in the Forth estuary at salinities <10‰, where high particulate loads of up to 180 mg l −1 occur. Phosphate removal is also observed in the Forth in this salinity range. The uranium removal rate in the upper part of this estuary is estimated at 44 kg y −1. The uranium concentrations and corresponding 234U 238U activity ratios measured for the freshwater end-members of the three rivers are: 0·15 μg l −1 and 1·65 for the Clyde 0·04 g −1 and 1·44 for the Tamar and 0·09 μg l −1 and 1·50 for the Forth. Regression analysis gives an overall U S ‰ ratio of (9·53 ± 0·84) × 10 −8 g g −1 over the salinity range 5·0–33·2‰ for all three estuaries, which is in excellent agreement with values obtained by other workers.

Anomalous behaviour of uranium isotopes in backwater sediments of Zuari river

The surface leaching of the labile component of uranium has been carried out in estuarine sediments of Zuari river in Goa. The measurements of alpha activities of238U,235U and234U in the leachates indicated a remarkable anomaly between the activities of238U and234U. The activity ratios of234U/238U in these leachates have been found to be in the range of 1.10 to 1.14. However, the activity ratios of235U/238U have been found to be 0.045 which is close to that in natural uranium. It has also been observed that the anomaly between238U and234U exists only on the surface organic layers of the backwater sediments of the Zuari river.

Uranium isotopes in rivers, estuaries and adjacent coastal sediments of western India: their weathering, transport and oceanic budget

The two major river systems on the west coast of India, Narbada and Tapti, their estuaries and the coastal Arabian sea sediments have been extensively studied for their uranium concentrations and 238U 238U activity ratios. The 238U concentrations in the aqueous phase of these river systems exhibit a strong positive correlation with the sum of the major cations, σ Na + K + Mg + Ca, and with the HCO 3 − ion contents. The abundance ratio of dissolved U to the sum of the major cations in these waters is similar to their ratio in typical crustal rocks. These findings lead us to conclude that 238U is brought into the aqueous phase along with major cations and bicarbonate. The strong positive correlation between 238U and total dissolved salts for selected rivers of the world yield an annual dissolved 238U flux of 0.88 × 10 10 g/ yr to the oceans, a value very similar to its removal rate from the oceans, 1.05 × 10 10 g/ yr, estimated based on its correlation with HCO 3 − contents of rivers. In the estuaries, both 238U and its great-grand daughter 234U behave conservatively beyond chlorosities 0.14 g/l. These data confirm our earlier findings in other Indian estuaries. The behavior of uranium isotopes in the chlorosity zone 0.02–0.14 g/l, was studied in the Narbada estuary in some detail. The results, though not conclusive, seem to indicate a minor removal of these isotopes in this region. Reexamination of the results for the Gironde and Zaire estuaries (Martin et al., 1978a and b) also appear to confirm the conservative behavior of U isotopes in unpolluted estuaries. It is borne out from all the available data that estuaries beyond 0.14 g/l chlorosities act neither as a sink nor as a source for uranium isotopes, the behavior in the low chlorosity zones warrants further detailed investigation. A review of the uranium isotope measurements in river waters yield a discharge weighted-average 238U concentration of 0.22 μg/l with a 234U 238U activity ratio of 1.20 ± 0.06 is missing. The residence time of uranium isotopes in the oceans estimated from the 238U concentration and the 234U 238U A. R. of the rivers yield conflicting results; the material balance of uranium isotopes in the marine environment still remains a paradox. If the disparity between the results is real, then an additional 234U flux of about 0.25 dpm/cm 2·10 3 yr into the oceans (about 20% of its river supply) is necessitated.

Studies on the geochemical behaviour of uranium isotopes in coastal environment of the east coast of india

Samples of coastal marine sediments of the East Coast of India were leached with a saturated solution of ammonium carbonate for the extraction of uranium from the sediment particle surface without attacking the mineral core of the particles. All the sediment samples were found to exhibit a234U/238U activity ratio in the range of 1.07 to 1.14. On removal of surface organic matter, the234U/238U activity ratio is close to 1.00, indicating that the anomaly between238U and234U exists only on the labile surface layer. However, no such variations are observed in235U/238U activity ratios. These ratios are close to 0.045 which is the same as that of natural uranium.

Studies on the geochemical behaviour of uranium isotopes in Tuwa springs and Khari river sediments

High activities of radium were observed in the spring waters of Tuwa in Panchamahal district of Gujarat state. These determinations have led to further studies on geochemical behaviour of uranium in the surface sediments of this region. Labile uranium from the surface of the sediment particles is leached with saturated solution of ammonium carbonate. Uranium is chemically separated from the leachates by cellulose column chromatography. Unusually high activity ratios of234U/238U in the range of 2.3 to 2.77 were observed on the surface of the particles. The core of the particles exhibited a ratio of 1.00 indicating soluble234U fraction has migrated.