Determination of uranium and thorium isotopes in mineral spring waters

Concentrations levels of uranium and thorium isotopes have been analyzed in the m mineral spring waters of a high background region of Brazil: Poços de Caldas and Águas da Prata. The procedure was based on the determination of²³⁸U,²³⁴U,²³²Th,²³⁰Th and²²⁸Th by -spectrometry after separation and purification of the isotopes of interest by using anion-exchange chromatography and preparation of the samples for -measurements by electrodeposition. The concentration varied from <1.1 to 28.4 mBq.l^–1 and from <1.6 to 141 mBq.l^–1 for²³⁸U and²³⁴U, respectively. Thorium isotope measurements varied from <0.2 to 1.8 mBq.l^–1 from <0.3 to 4.9 mBq.l^–1 and from <0.8 to 19.9 mBq.l^–1 for²³²Th,²³⁰Th and²²⁸Th, respectively. Calculations of thorium and uranium isotopic activity ratios were carried out giving values ranging from 1.9 to 7.2, from 1.2 to 3.0 and from 7.7 to 15.3 for²³⁴U/²³⁸U,²³⁰Th/²³²Th and²²⁸Th/²³²Th, respectively. The effective doses due to the intake of²³⁸U and²³⁴U present in these waters are expected to reach values up to 1.4×10^–3 mSv y^–1 and 8.0×10^–3 mSv y^–1, respectively.     

Behavior of uranium and thorium isotopes in soils of the Boréon area, Mercantour Massif (S.E. France): Leaching and weathering rate modeling

Four cores were collected in weathered rocks and soils in the Boréon forest area (1765 m, Mercantour Massif, France). The samples were analyzed for the isotopes ²³⁰Th, ²³²Th, ²³⁴U and ²³⁸U. The activity and isotopic ratio profiles suggest that uranium was mobilized (leaching and precipitation) during the weathering process, as well as thorium but in a much less proportion. A model was drawn up to evaluate the U leaching rate and the time that some levels of the weathered rocks have been subjected to weathering. It utilizes LATHAM and SCHWARCZ’s two equations,¹⁵ expressed as ²³⁴U/²³⁸U and ²³⁰Th/²³⁸U activity ratios, which assume that the alpha recoil effect allows easier leaching for ²³⁴U than ²³⁸U and no Th mobility. But this last assumption does not correspond to the observations made in the Boréon area, since it appears that in some soil deeper layers ²³⁰Th and ²²⁸Th are in radioactive deficit relatively to their parents. As there are four unknown quantities (the time, the leaching rates of ²³⁸U, ²³⁴U, ²³⁰Th), the problem to be solved requires two more equations; these can be obtained utilizing the U activity ratio in water, and taking into account the ²³²Th behavior. In some sites the ²³⁸U leaching rate is high in deeper soil levels (near the fresh rocks); this would correspond to a loss of half the U amount in less than 24 000 years.     

Evaluation of metal and radionuclide data from neutron activation and acid-digestion-based spectrometry analyses of background soils: Significance in environmental restoration

A faster, more cost-effective, and higher-quality data acquisition for natural background-level metals and radionuclides in soils is needed for remedial investigations of contaminated sites. The advantages and disadvantages of neutron activation analysis (NAA) compared with those of acid-digestion-based spectrometry (ADS) methods were evaluated using Al, Sb, As, Cr, Co, Fe, Mg, Mn, Hg, K, Ag,²³²Th,²³⁵U,²³⁸U, V, and Zn data. The ADS methods used for this project were inductively coupled plasma (ICP), ICP-mass spectrometry (ICP-MS), and alpha spectrometry. Scatter plots showed that the NAA results for As, Co, Fe, Mn,²³²Th, and²³⁸U are reasonably correlated with the results from the other analytical methods. Compared to NAA, however, the ADS methods underestimated Al, Cr, Mg, K, V, and Zn. Because of the high detection limits of ADS methods, the scatter plots of Sb, Hg, and Ag did not show a definite relationship. The NAA results were highly correlated with the alpha spectrometry results for²³²Th and²³⁸U but poorly correlated for²³⁵U. The NAA, including the delayed neutron counting, was a far superior technique for quantifying background levels of radionuclides (²³²Th,²³⁵U, and²³⁸U) and metals (Al, Cr, Mg, K, V, and Zn) in soils.     

Factors Controlling Natural Radionuclides Migration in Sedimentary Rock Samples,Gabal Um‐Hamd,Southwestern Sinai,Egypt

The activity concentrations of some radionuclides (²³⁸U, ²³⁴U, ²³⁰Th, ²²⁶Ra, ²³²Th, ⁴⁰K and ²³⁵U) were measured by γ‐ray spectrometry in order to study their behavior and the relation between them in Carboniferous rock samples collected from Gabal (mountain) Um‐Hamd, southwestern Sinai, Egypt. The whole samples are located in the two limbs and trough of a synclinal form structure to identify the radionuclides migration processes which have occurred in these rock samples. The average activity concentrations of ²³⁸U, ²³²Th, ²²⁶Ra, and ⁴⁰K measured in the all samples except sandy dolostone sample are higher than the worldwide average values as reported by UNSCEAR 2008. The activity ratios (²³⁴U/²³⁸U) for half of the samples are in equilibrium, while the other half samples are below unity indicates migration‐out of uranium. The hazard indices were also calculated. The variations in lithologic types and the configuration of the structural synform played its roles beside the physical and chemical properties of different radionuclides in their fractionations.     

Radioactive series disequilibria in underground uranium deposits of the Singhbhum Shear Zone, Eastern India

Radionuclides of the ²³⁸U series (²²⁶Ra, ²¹⁰Pb, ²³⁴Th and ²³⁴U), ²³⁵U series (²²⁷Ac and ²³¹Pa) and ²³²Th series (²²⁸Th and ²²⁸Ra) series were measured by High Resolution Gamma Spectrometry system in twenty-five uranium ore samples from underground uranium deposits in the Singhbhum Shear Zone of Eastern India. The activity concentrations were observed to vary within a wide range in most of the deposits, as is the case in most rocks of crustal origin. The uranium ore from these deposits were not of high ore grade (U concentrations ranged from 0.015 to 0.082%). Activity ratios of key daughter–parent pairs from the decay chains, viz. ²²⁶Ra/²³⁸U, ²²⁶Ra/²¹⁰Pb, ²³¹Pa/²³⁵U, ²²⁷Ac/²³⁵U, ²³⁰Th/²³⁸U, ²³⁴U/²³⁸U, ²²⁶Ra/²³⁰Th and ²²⁸Th/²²⁸Ra indicated migration/accumulation of uranium and radium in some samples. The ²²⁶Ra/²³⁰Th ARs suggested that the deposits were not closed to groundwater movement for a maximum time period of 8ky. Thiel plot of the ²³⁴U/²³⁸U vs. ²³⁰Th/²³⁸U activity ratios indicated uranium accumulation and complex processes of uranium redistribution.     

Investigation of radioactive lead,uranium, and thorium in environmental waters by extraction chromatography resins

A time-saving and sensitive method for monitoring low concentration (activities) of ²¹⁰Pb, ²³²Th, and ²³⁰Th and ²³⁸U, ²³⁴U, and ²³⁵U in water samples has been developed. Through the combination of co-precipitation and extraction chromatography by 3M RAD disks and UTEVA (Eichrom) columns effective radiochemical separation of the analytes was carried out. Thorium and uranium activities were determined by alpha spectrometry and lead activity by LSC, respectively. The minimal detectable activities obtained were 0.6?Bq?m^?3 for uranium, 0.29?Bq?m^?3 for thorium, and 2.5?Bq?m^?3 for ²¹⁰Pb. More than 150 different waters were analysed for uranium content and only 30 for lead and thorium. The investigations are still in progress.     

Radium,uranium and thorium concentrations in low specific activity scales and in waters of some oil and gas production plants

Low specific activity scales consisting of alkaline earth metal carbonates and sulfates are often present in some gaseous and liquid hydrocarbon plants; these scales contain a certain concentration of radium, uranium and thorium, which can cause a risk of -irradiation and of internal radiocontamination when they must be mechanically removed. That being stated,²³⁸U,²³²Th and²²⁶Ra were determined in scales, sludges and waters coming from different plants.²³⁸U and²³²Th concentrations were found very low; the isotopes²³⁸U and²³⁴U resulted in radioactive equilibrium, whilst²³²Th and²²⁸Th were not always in equilibrium.²²⁶Ra concentration was higher in scales and sludges than in waters.     

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.     

Development of a sequential method for the determination of238U,234U,232Th,230Th,228Th,228Ra,226Ra,and210Pb. in environmental samples

A sequential analytical method for the determination of²³⁸U,²³⁴U,²³²Th,²³⁰Th,²²⁸Th,²²⁸Ra,²²⁶Ra and²¹⁰Pb in environmental samples was developed. Uranium and thorium isotopes are first chromatographically sepaaated using tri-n-octyl phosphine oxide (TOPO) supported on silica gel. The uranium isotopes are determined by alpha-spectrometry following extraction with TOPO onto a polymeric membrane. Thorium isotopes are co-precipitated with lanthanum fluoride before counting in an alpha spectrometer. Radium isotopes and²¹⁰Pb are separated by co-precipitation/precipitation with mixed barium/lead sulphate. Radium-226 is determined by gross alpha counting of the final BaSO₄ precipitate and²²⁸Ra by gross beta counting of the same source. Lead-210 is determined through beta counting of its daughter product²¹⁰Bi.     

Fractionation of thorium and uranium isotopes in the acid leaching experiments on monazite

A series of leaching experiments with water and gradually harsher acid solutions have been carried out on a monazite.²²⁸Th/²³²Th,²³⁰Th/²³²Th, and²³⁴U/²³⁸U activity ratios in the acid fractions show a common variation pattern: high — low — close to bulk values, which can be explained in terms of preferential solution effect of recoil atoms. Compared with²²⁸Th, the preferential solution effect of²³⁴U is suppressed due to self-annealing of recoil tracks.     

Determination of uranium isotopes in environmental samples

The determination of isotopes of uranium by alpha spectrometry in different environmental components (sediments, soil, water, plants and phosphogypsum) is presented and discussed in this paper. The alpha spectrometry is a very convenient and good technique for activity concentration of natural uranium isotopes (²³⁴U, ²³⁵U, ²³⁸U) in environmental samples and provides the most accurate determination of isotopic activity ratios between ²³⁴U and ²³⁸U. The analysis were provided information about possible sources of high concentrations of uranium in the examined sites determined by anthropogenic sources. The calculation of values ²³⁴U/²³⁸U in all analyzed samples was applied to identifying natural or anthropogenic uranium origin. Activity concentration of uranium isotopes in analyzed environmental samples shows that measurement of uranium levels is of great importance for environmental and safety assessment especially in contaminated areas (phosphogypsum waste heap).     

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.     

Natural radioactivity in bioassay by alpha-spectrometry measurements

Personnel of nuclear facilities are checked regularly for internal contamination by bioassay measurements. Although these persons are generally not involved in any incident, natural radioactivity from U, Th and Ra can be found in their urine or faeces. Uranium total activity in urine has been found with a range of 0.051 to 3.0 mBq/24 h and in faeces from 14.5 to 380 mBq/d. ²³⁴U/²³⁸U ratio for urine is 1.48 but this ratio varies from 0.47 to 19. By comparison, the ²³⁴U/²³⁸U ratio found in urine from workers in volved with natural uranium or 4.5% enriched uranium is 1.0 and around 4.0 respectively. ²³⁰Th, ²²⁸Th and sometimes ²³²Th have also been detected. The total thorium activity varies from 0.137 to 5.6 mBq/24 h in urine and from 9 to 183 mBq/d in faeces. ²²⁸Th has generally been found in excess of ²³²Th. All these measurements were performed by alpha-spectrometry. The few ²²⁶Ra results have been measured using the Lucas or emanation method.     

Measurements of238U,234U and230Th in impure carbonates for age determination

The carbonate cements of conglomeritic deposits of late Pleistocene age have been leached with 0.2N hydrochloric acid and analyzed radiochemically. The leachate and the residue fractions were separately measured for²³⁸U,²³⁴U and²³⁰Th, using isotope-dilution and alpha-spectrometric techniques. The data are used to estimate the isotopic activities of uranium and thorium in the carbonate phase. These activities give age information for the carbonate cementation. Ages in the range of 185–320·10³ years were obtained for the samples studied.     

Uranium age-dating using in-situ isotope ratios by thermal ionization mass spectrometry for nuclear forensics

The model dates of two enriched uranium materials were determined using a new method for nuclear forensics investigation. In this method, without spike addition, the ²³⁰Th/²³⁴U ratio was calculated from the measured ratios of ²³⁰Th/²³⁴Th and ²³⁴U/²³⁸U and from calculated ²³⁴Th/²³⁸U ratio in secular equilibrium. The model date obtained for the low-enriched uranium material was in agreement with the known production date. For the highly enriched uranium material, a more recent model date than the known production date was obtained. The ²³⁴U interference on ²³⁴Th counting in thermal ionization mass spectrometer measurement was suspected as a potential cause.

     

Microwave oven dissolution of geological samples: Novel application in the determination of natural decay series radionuclides

A microwave oven was utilised to decompose several geological materials by means of acid digestion. Dissolution was achieved in 5 min and²³⁸U,²³⁴U,²³²Th and²³⁰Th were all determined on the solutions by radiochemical separation and -spectrometry. The materials, which include a granite, an arkose, a river sediment and a nearshore marine sediment, display a large range in U and Th contents /Th/U ratio of 0.7 to 7: U content of 12 to 1400 Bq kg^–1/ and activity ratios /²³⁴U/²³⁸U of 0.95 to 1.50/. The data indicate that the microwave oven dissolution method produces data comparable to the traditional /open beaker/ method. Unit costs are, however, significantly reduced.     

Thorium,uranium and plutonium isotopes in the Arkansas River

Radiochemical measurements of the concentrations of thorium, uranium and plutonium isotopes were carried out for the samples of Arkansas River collected at six locations in the states of Colorado and Oklahoma. The uranium to thorium ratios in the river samples were found to be highly variable and generally much greater than the ratios found in soils and in rainwater. An attempt has been made to determine the apparent²³⁰Th ages (or the times which elapsed since the last major disruption of the radioactive equilibria) from the observed²³⁰Th/²³²Th and²³⁴U/²³²Th ratios in the water samples.     

Determination of228Th,230Th,and232Th in environmental samples from uranium mining and milling operations

A method is described for the determination of²²⁸Th,²³⁰Th, and²³²Th in environmental samples from uranium mining and milling operations. The analytical procedure is based on the direct determination of²²⁸Th in the sample by high resolution γ-spectrometry followed by extraction and purification of the thorium fraction using high molecular weight amines and an anion-exchange technique, respectively, prior to α-spectrometry to determine isotopic ratios. The lowest level of detection for each thorium isotope is 0.01 pCi/g for solid samples and 20 pCi/l for aqueous samples. Replicate analyses of a typical mine waste stream gave a standard deviation of ±3% for²²⁸Th. Standard deviations of the²³⁰Th and²³²Th increased to ±11% apparently due to traces of²¹⁰Po interfering in the α-spectrometry.     

The dietary intake of238U,234U,230Th,232Th,228Th and226Ra from food and drinking water by inhabitants of the Walbrzych region

Intake with food and water of the natural radionuclides of the uranium and thorium series was determined for adult population of the south-western region in Poland, where in the 1950-ies an exploration of uranium ore was conducted. Concentration of the radionuclides was determined in food products and drinking water and their annual intake was estimated on the basis of the average annual consumption. The intake of²³⁸U,²³⁴U and²³⁰Th occurred mainly with water (33% to 68%), whereas the intake of²³²Th,²²⁸Th and²²⁶Ra was mainly with vegetables, potatoes, milk and flour. From the intake and dose coefficients the annual effective doses from the ingested radionuclides were calculated. The total dose was 5.6 Sv, of which 74% originated from²²⁶Ra.     

Determination of Uranium and Thorium Isotope Ratios by Inductively Coupled Plasma Mass Spectrometry

Measurement conditions were selected and a procedure was proposed for determining the ²³⁴U/²³⁸U and ²³⁰Th/²³²Th isotope ratios using an ELEMENT single-channel double-focusing inductively coupled plasma mass spectrometer. The procedure was tested in analyzing bottom sediments from Lake Baikal with the extraction preconcentration of uranium and thorium. The accuracy of the procedure was verified using certified reference materials and a model solution by comparing the results obtained with the data of spectrometry.