Uranium fallout from the nuclear-powered satellites and volcanic eruptions

Increasing trends of the concentrations of²³⁴U,²³⁵U and²³⁸U in rain observed during the period between April 1984 and June 1985 at Fayetteville (36°N, 94°W), Arkansas, and peak concentrations of²³⁴U and²³⁵U observed in a number of rain samples collected during the months of May and June 1985 appear to be the effects of delayed fallout from the 1982 eruption of El Chichón volcano and the 1983 fall of the nuclear-powered satellite Cosmos-1402, respectively.This investigation was supported by the National Science Foundation under Grant ATM 84-07618.     

Variation of the thorium to uranium ratio in rain: Thorium-230 chronology of the eruptions of Mt. St. Helens and El Chichón volcanoes

Principles of the thorium-230 dating method were applied to the study of thorium and uranium isotopes in a series of rain samples collected at Fayetteville (36°N, 94°W), Arkansas, since 1980. The results indicate that the rainwater contains volcanic ash materials with a wide variety of ages, which were blown up onto the upper stratosphere from the 18 May 1980 eruption of Mount St. Helens and the 28 March 1982 eruption of E1 Chichón. These volcanic materials seem to have stayed airborne for a number of years and profoundly affected the global atmospheric inventories of thorium and uranium isotopes.This investigation was supported by the National Science Foundation under Grant ATM 84-07618.     

Effect of the eruptions of Mount St. Helens and El Chichon on the ratios of thorium and uranium isotopes in rain

Marked variations in the ratios of²²⁸Th/²³²Th,²³⁰Th/²³²Th and²³⁸U/²³²Th ratios were observed in rain samples collected at Fayetteville (36°N, 94°W), Arkansas, during 1980 through 1983. These variations are attributed to the fallout from the 1980 and 1982 eruptions of Mount St. Helens and El Chichón volcanoes.This investigation was supported by the National Science Foundation under Grant ATM 84-07618.     

Fallout of thorium and uranium isotopes from the 1982 eruption of El Chichón volcano

Marked increases in the concentrations of thorium and uranium isotopes observed in rain samples collected at Fayetteville (36° N, 94° W), Arkansas, during 1983 are attributed to the fallout from the 1982 eruption of El chichón volcano in Mexico.This investigation was supported by the National Science Foundation under Grant ATM 82-06718 and ATM 84-07618.     

Plutonium fallout from the nuclear-powered satellite Cosmos-1402

Radiochemical measurements of^239,240Pu were carried out for a total of 57 individual rain and snow samples collected at Fayetteville (36 °N, 94 °W), Arkansas, during the period between November 1984 and June 1986. The results indicate that the fallout of plutonium observed during the past three years is due, primarily, to the nuclear debris originating from the 7 February 1983 burn-up of the nuclear-powered Soviet satellite Cosmos-1402.This investigation was supported by the National Science Foundation under Grant ATM 84-07618.     

Determination of234U/238U activity ratios in Syrian phosphates

The concentrations of uranium and the²³⁴U/²³⁸U ratio in natural Syrian phosphates were measured by gamma- and alpha-ray spectroscopy. The²³⁴U/²³⁸U activity ratios showed that uranium in Syrian phosphate is in equilibrium under the climatic conditions. Soma anomalous observations in these ratios were explained by earlier leaching of the phosphate by water (rain or other).     

Uranium isotope anomaly in minerals

A series of leaching experiments with HF, HCl, HNO₃ were carried out on samples of uranium minerals (uraninite and carnotite samples). Anomalously high²³⁴U/²³⁸U ratios were observed in some uranium fractions. The observed²³⁴U/²³⁸U activity ratios varied between the values of 1.019±0.155 and 6.210±0.504 (Ci/Ci), while the bulk carnotite sample had an activity ratio of 1.010±0.005 (Ci/Ci). These results are interpreted as due to alpha-recoil effect and changes in oxidation state of uranium.     

Activity concentrations of238U and226Ra in agricultural samples

Distributions of²³⁸U and²²⁶Ra in agricultural samples and cultivated soils have been studied over ten years. The crops are rice, spinach and Chinese cabbage. Two investigated areas have been selected (35° 18 N, 113° 35 E). The agricultural samples and soils were collected annually from May 1982 through October 1991. The activity concentrations of²²⁶Ra in agricultural samples are greater than those of²³⁸U. The transfer factors of²³⁸U,²²⁶Ra are from 0.06·10^–3 to 1.2·10^–3. The²²⁶Ra/²³⁸U ratios for three agricultural samples have their characteristic values.     

Uranium-235 fallout from the nuclear-powered satellite Cosmos-1402

The presence of excess uranium-235 was detected in many of the rain samples collected at Fayetteville (36°N, 94°W), Arkansas, during the period between April 1983 and March 1984. The experimental data indicate that the uranium-235 originated from the nuclear reactor on board the Soviet satellite Cosmos-1402, which fell over the South Atlantic Ocean on 7 February 1983.This investigation was supported by the National Science Foundation under Grant ATM 82-06718 and ATM 84-07618.     

Anomalous behaviours of protactinium in the acid-leaching experiments on pitchblende

A series of leaching experiments with H₂O, HCl, HNO₂ and HF were carried out on a sample of pitchblende from Africa. Anomalously high²³¹Pa/²³⁵U ratios, which were not accompanied by similar enhancements of²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios, were observed in some uranium fractions. The observed²³¹Pa/²³⁵U ratios varied between the values of 0.035±0.005 and 2,000±300 (Ci/Ci). These results are interpreted as due, primarily, to the difference in the chemical properties of protactinium and uranium, rather than to the alpha-recoil effects.     

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.     

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.     

Behavior of uranium along Jucar River (Eastern Spain): Determination of234U/238U and235U/238U ratios

The uranium concentration and the²³⁴U/²³⁸U,²³⁵U/²³⁸U activity ratios were studied in water samples from Jucar River, using low-level -spectrometry. The effects of pH, temperature and salinity were considered and more detailed sampling was done in the neighbourhood of Cofrentes Nuclear Plant (Valencia, Spain). Changes were observed in the uranium concentration with the salinity and the²³⁴U/²³⁸U activity ratio was found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes in the concentration of uranium and the activity ratios.     

Uranium isotopes as a tracer of groundwater transport studies

The activity concentrations of ²³⁴U and ²³⁸U in thermal groundwater, deep well water and river water samples from Central Poland were determined. Concentration of ²³⁴U and ²³⁸U in the examined waters varied from <0.013 (LLD) to 16.8 mBq/dm³ and from <0.013 (LLD) to 45.5 mBq/dm³ respectively. The highest uranium activity concentrations were measured in the thermal groundwater from Mszczonow and Cieplice, while the lowest were observed in thermal ground water from Uniejow and Poddebice. In thermal groundwater from Skierniewice, uranium activity concentrations were below lower limit of detection (0.013 mBq/dm³). The ²³⁴U/²³⁸U activity ratio varied from 0.37 (Cieplice) to 1.30 (Poddebice well water).     

A comparative study of234U/238U alpha-activity ratios determined by alpha-spectrometry and calculated from mass spectrometric data

²³⁴U/²³⁸U α-activity ratios determined by α-spectrometry (AS) and those calculated from the atom ratio data using the half-life values are compared in some of the isotopic reference materials of uranium and a few other uranium samples. For α-spectrometry, electrodeposited sources were prepared and a large area passivated ion implanted (IPE) detector (450 mm²) was used for recording the α-spectra. The isotopic composition of U was determined by thermal ionisation mass spectrometry (TIMS) and the recommended half-life values of²³⁴U and²³⁸U were used to calculate the α-activity ratio. It is observed that²³⁴U/²³⁸U α-activity ratios calculated from the atom ratio data are consistently high, with a mean difference of about 5%, when compared to the α-spectrometry results. This discrepancy warrants confirmation by a few more laboratories and suggests redetermination of the half-life values of²³⁴U and²³⁸U.     

The transfer of uranium from sediment to water along Jucar River, Spain

The effect of sediment size, pH, temperature and conductivity on the transfer of uranium from sediment to water has been studied. The uranium concentration and the²³⁴U/²³⁸U,²³⁵U/²³⁸U activity ratios were measured in water, sediments and suspended matter sampled from Jucar River, using low level alpha-spectrometry. Distribution factors were obtained from these measurements. A more detailed sampling was done in the neighbourhood of the Cofrentes Nuclear Plant (Valencia, Spain). Total uranium activity,²³⁴U/²³⁸U activity ratio and distribution factors for²³⁴U and²³⁸U were found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes.     

Atmospheric residence times of strontium-90 and lead-210

The concentrations of⁸⁹Sr,⁹⁰Sr,²¹⁰Pb and²¹⁰Po were measured in a series of rain samples collected at Fayetteville (36°N, 94°W), Arkansas, after the 14th Chinese test of March 18, 1972, which occurred at Lop Nor (40°N, 90°E), China. Approximately concordant tropospheric residence times were obtained from the⁸⁹Sr/⁹⁰Sr and²¹⁰Po/²¹⁰Pb ratios in rain. The⁸⁹Sr/⁹⁰Sr ratios were also measured for the rain samples collected at Tokyo (36°N, 140°E), Japan, and at Ankara (40°N, 33°E), Turkey.     

Determination of U isotope ratios in sediments using ICP-QMS after sample cleanup with anion-exchange and extraction chromatography

The determination of uranium is important for environmental radioactivity monitoring, which investigates the releases of uranium from nuclear facilities and of naturally occurring radioactive materials by the coal, oil, natural gas, mineral, ore refining and phosphate fertilizer industries, and it is also important for studies on the biogeochemical behavior of uranium in the environment. In this paper, we describe a quadrupole ICP-MS (ICP-QMS)-based analytical procedure for the accurate determination of U isotope ratios (²³⁵U/²³⁸U atom ratio and ²³⁴U/²³⁸U activity ratio) in sediment samples. A two-stage sample cleanup using anion-exchange and TEVA extraction chromatography was employed in order to obtain accurate and precise ²³⁴U/²³⁸U activity ratios. The factors that affect the accuracy and precision of U isotope ratio analysis, such as detector dead time, abundance sensitivity, dwell time and mass bias were carefully evaluated and corrected. With natural U, a precision lower than 0.5% R.S.D. for ²³⁵U/²³⁸U atom ratio and lower than 2.0% R.S.D. for ²³⁴U/²³⁸U activity ratio was obtained with less than 90 ng uranium. The developed analytical method was validated using an ocean sediment reference material and applied to an investigation into the uranium isotopic compositions in a sediment core in a brackish lake in the vicinity of U-related nuclear facilities in Japan.     

A combined method of neutron activation analysis and radiometric measurements for <Superscript>234</Superscript>U and <Superscript>238</Superscript>U determination in soil samples of low uranium concentration

A method that combines the use of non-destructive neutron activation analysis and high-resolution α spectrometry has been developed for determination of the activities of ²³⁴U and ²³⁸U in geological samples of low uranium content. The ²³⁸U content is determined by k₀-based neutron activation analysis, whereas the ²³⁴U/²³⁸U relationship is measured by α spectrometry after isolation and electrodeposition of the uranium extracted from a lixiviation with 6 M HCl. The main advantage of the method is the simplicity of the chemical operations, including the fact that the steps destined to assure similar chemical state for the tracer and the uranium species present in the sample are not necessary. The method was applied to soil samples from sites of the North Peru Coast. Uranium concentration range 3–40 mg/kg and the isotopic composition correspond to natural uranium, with about 10% uncertainty.     

Determination of uranium isotopes in environmental samples by alpha-spectrometry

A new and accurate method for the determination of uranium isotopes (²³⁸U, ²³⁴U and ²³⁵U) in environmental samples by alpha-spectrometry has been developed. Uranium is preconcentrated from filtered water samples by coprecipitation with iron(III) hydroxide at pH 9-10 using an ammonia solution and the precipitate is dissolved in HNO₃ and mineralized with H₂O₂ and HF; uranium in biological samples is ashed at 600 °C, leached with Na₂CO₃ solution and mineralised with HNO₃, HF and H₂O₂; uranium in soil samples is fused with Na₂CO₃ and Na₂O₂ at 600 °C and leached with HCl, HNO₃ and HF. The mineralized or leaching solution in 2M HNO₃ is passed through a Microthene-TOPO (tri-octyl-phosphine oxide) column; after washing, uranium is directly eluted into a cell with ammonium oxalate solution, electrodeposited on a stainless steel disk and measured by alpha-spectrometry. The lower limits of detection of the method is 0.37 Bq^.kg^-1 (soil) and 0.22 mBq^.l^-1 (water) for ²³⁸U and ²³⁴U and 0.038 Bq^.kg^-1 (soil) and 0.022 mBq^.l^-1 (water) for ²³⁵U if 0.5 g of soil and 1 litre of water are analyzed. Five reference materials supplied by the IAEA have been analyzed and reliable results are obtained. Sample analyses show that, the ²³⁸U, ²³⁴U and ²³⁵U concentrations are in the ranges of 0.30-103, 0.49-135 and 0.02-4.82 mBq^.l^-1 in waters, of 1.01-7.14, 0.85-7.69 and 0.04-0.32 Bq^.kg^-1 in mosses and lichens, and of 25.6-53.1, 26.4-53.8 and 1.18-2.48 Bq^.kg^-1 in sediments. The average uranium yields for waters, mosses, lichens and sediments are 74.5±9.0%, 80.5±8.3%, 77.8±4.9% and 89.4±9.7%, respectively.