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.     

Radioactivity distribution of thorium in sediment core of the Sabah-Sarawak coast

Thorium activity concentrations were measured in seven marine sediment cores taken from Sabah-Sarawak coast on 2004 by using a gravity box corer. Collected sediments were generally homogenous mud which contained much more mixture of silt and clay compared to sand and relatively low content of organic carbon (i.e. less than 5% at all sampling stations). The results found that activity concentrations of ²³⁰Th, ²³²Th and ratios of ²³⁰Th/²³²Th were ranged from 6.5–20.4 Bq/kg dry wt., 6.8–27.8 Bq/kg dry wt. and 0.69–0.92, respectively. It seem that, ²³²Th activity concentrations are slightly higher than ²³⁰Th at all sampling stations and both radionuclides were generally high at Sabah compared to Sarawak coastal waters. ²³⁰Th activity concentrations in sediment core appear to be correlated with the activity concentrations of ²³²Th at some sampling station. These indicating both radionuclides were supplied from the same of environment and source origin of detrital from terrestrial and shallower water. The low ²³⁰Th/²³²Th activity ratio which is less than unity suggesting that ²³²Th was actively and rapidly regenerated compared to ²³⁰Th from ²³⁴U. It also can be attributed to less efficiently scavenge of ²³⁰Th onto particles prior deposited at the marine sediment bed.     

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.     

Preparation and certification of new thorium isotopic reference materials

Preparation of two Isotopic Reference Materials of thorium has been performed, starting from highly enriched ²³²Th (99.99%) and ²³⁰Th (99.8%). After full characterization (chemical and isotopic) of these purified base materials the thorium nitrate was transformed to thorium dioxide. Accurately weighed amounts of the two isotopes in the dioxide form were subsequently dissolved in nitric acid and resulted in solutions with amount ratios n(²³⁰Th)/n(²³²Th) close to 10^–5 (IRMM-035) and 3 · 10^–6 (IRMM-036). These gravimetrically prepared ratios were finally verified by means of Thermal Ionization Mass Spectrometry (TIMS). The purpose of the Reference Materials is to calibrate thorium isotope amount ratio measurements. Received: 7 July 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

Preparation and certification of new thorium isotopic reference materials

Preparation of two Isotopic Reference Materials of thorium has been performed, starting from highly enriched ²³²Th (99.99%) and ²³⁰Th (99.8%). After full characterization (chemical and isotopic) of these purified base materials the thorium nitrate was transformed to thorium dioxide. Accurately weighed amounts of the two isotopes in the dioxide form were subsequently dissolved in nitric acid and resulted in solutions with amount ratios n(²³⁰Th)/n(²³²Th) close to 10^–5 (IRMM-035) and 3 · 10^–6 (IRMM-036). These gravimetrically prepared ratios were finally verified by means of Thermal Ionization Mass Spectrometry (TIMS). The purpose of the Reference Materials is to calibrate thorium isotope amount ratio measurements. Received: 7 July 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

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.     

Thorium series disequilibrium and geochemical processes in estuarine sediments of Mandovi river

The measurements of natural radioactivity due to thorium isotopes have been carried out in estuarine sediments of Mandovi river (Goa). The geochemical behaviour of these sediments has been studied by leaching the samples with 5 % ethylenediaminetetraacetic acid at pH 3.0 in order to investigate the processes occurring on the surface of the sediment particles and the distribution of natural thorium in estuarine sediments. The²²⁸Th/²³²Th activity ratios have been found to be in the range of 2.00 to 2.12. This anomaly between²³²Th and²²⁸Th has been attributed to the preferential leaching of²²⁸Ra by water flowing over these sediments. The activities of²²⁸Ra on the surface labile layers of the sediments have also been determined. The²³⁰Th/²³²Th activity ratios have been found to be in the range of 0.94 to 1.04. These ratios are mainly dependent on the precipitation action of²³⁰Th on adjacent sediments.     

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.     

Determination of 232Th in seawater by ICP-MS after preconcentration and separation using a chelating resin

This article describes an analytical method for the separation, preconcentration and determination of ²³²Th in seawater samples at sub-ng/L levels using a NOBIAS CHELATE PA1 resin and a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). The resin showed excellent adsorption of ²³²Th at a low pH of 2.4 ± 0.4 in a relatively small volume (200 mL) of seawater. ²³²Th adsorbed on the resin was easily eluted using 5 mL of 0.8 M HNO₃. An enrichment factor of 40 was achieved for ²³²Th analysis. Ethylenediamine-tetraacetic acid disodium salt dehydrate (EDTA) was used to investigate the effect of ²³²Th-binding organic ligand on the retention of ²³²Th on the chelating resin. Results obtained using acidified samples (pH of 2.4 ± 0.4) showed EDTA had no significant effect on ²³²Th recovery, indicating that at this low pH, ²³²Th was dissociated from the ²³²Th-binding organic ligand and quantitatively retained on the NOBIAS CHELATE PA1 resin. The developed analytical method was characterized by a separation and preconcentration taking approximately 4 h and a low detection limit of 0.0038 ng/L for ²³²Th, and was successfully applied to the determination of ²³²Th in seawater samples collected from coastal areas, Japan.     

Geochemical record of U and Th isotopes in bottom sediments of Lake Kawaguchi at the foot of Mt. Fuji, Central Japan

Sediment cores from Lake Kawaguchi at the foot of Mt. Fuji in Japan were analyzed for U and Th isotopes (²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th and ²²⁸Th) in the light of the linkage to paleoenvironmental changes. These isotopic concentrations and their ratios varied widely with depth of sediment core. A marked disequilibrium (1.1–1.5) higher than the value of 1.0 was observed for ²³⁴U/²³⁸U activity ratios, indicating that U from lake water with high ²³⁴U/²³⁸U ratio (ca. 1.6) was transferred to the bottom sediment by adsorption and/or adhesion onto the settling particles. By using model equations, the U found in the sediment core was separated into lithogenous and autogenous U fractions. These depth profiles were compared with parameters such as organic matter and biogenic-SiO₂ contents and amount of rainfall. Some variations of selected parameters with depth coincided with those of lithogenous or autogenous U. The results obtained suggest that variation in the lithogenous and/or autogenous U in the sediment with depth might be helpful in tracing the geochemical behavior of U and the past environmental changes in the area surrounding Lake Kawaguchi.The authors would like to express their gratitude to Dr. Y. Ohtsuka of Department of Radioecology, Institute for Environmental Sciences and Dr. K. Sasaki of Department of Cultural Properties and Heritage, Kanazawa Gakuin University for sampling of water and rock samples at Lake Kawaguchi.     

Geochemical record of U and Th isotopes in bottom sediments of Lake Kawaguchi at the foot of Mt. Fuji, Central Japan

Sediment cores from Lake Kawaguchi at the foot of Mt. Fuji in Japan were analyzed for U and Th isotopes (²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th and ²²⁸Th) in the light of the linkage to paleoenvironmental changes. These isotopic concentrations and their ratios varied widely with depth of sediment core. A marked disequilibrium (1.1–1.5) higher than the value of 1.0 was observed for ²³⁴U/²³⁸U activity ratios, indicating that U from lake water with high ²³⁴U/²³⁸U ratio (ca. 1.6) was transferred to the bottom sediment by adsorption and/or adhesion onto the settling particles. By using model equations, the U found in the sediment core was separated into lithogenous and autogenous U fractions. These depth profiles were compared with parameters such as organic matter and biogenic-SiO₂ contents and amount of rainfall. Some variations of selected parameters with depth coincided with those of lithogenous or autogenous U. The results obtained suggest that variation in the lithogenous and/or autogenous U in the sediment with depth might be helpful in tracing the geochemical behavior of U and the past environmental changes in the area surrounding Lake Kawaguchi.The authors would like to express their gratitude to Dr. Y. Ohtsuka of Department of Radioecology, Institute for Environmental Sciences and Dr. K. Sasaki of Department of Cultural Properties and Heritage, Kanazawa Gakuin University for sampling of water and rock samples at Lake Kawaguchi.     

Regional characteristics of naturally occurring radionuclides in surface sediments of Chinese deserts and the Keum River area of Korea

Naturally occurring radionuclides (NORN) such as ⁴⁰K, ²²⁶Ra and ²³²Th from 44 surface sediment samples collected from four desert regions of Chinese were determined to investigate the regional characteristics of the source areas of Asian dust. The radionuclides for 41 surface sediment samples collected from seven sites of the Keum River area in Korea were also determined to compare the regional characteristics with the Chinese desert area. The specific activities (SA) and the specific activity ratios (SAR) of the radionuclides were investigated for distinguishing the source region of Asian dust. The SA of ²²⁶Ra and ²³²Th as well as the SAR of ²²⁶Ra/⁴⁰K and ²³²Th/⁴⁰K were found to be useful to characterize source area and tracing Asian dust.     

Low level measurements of thorium and neptunium in environmental samples using the (γ, f) reaction

A new highly sensitive track method for the determination of thorium (²³²Th) and neptunium (²³⁷Np) has been developed. The technique includes the radiochemical separation procedure of the isotopes followed by the irradiation of the resultant samples on the MT-25 microtron. The detection limit is équivalent up to 3·10^–13 g of²³²Th and 7·10^–14 of²³⁷Np. The method was used to determine²³²Th and²³⁷Np isotopes in water samples.     

Interlaboratory comoparison of analytical methods for the determination of natural series uranium and thorium isotopes in rock samples

Results are repoerted for²³⁸U,²³⁴U,²³²Th, and²³⁰Th determinations in 19 rock samples from a uranium mine, performed independently, byb three different laboratories. Uranium and thorium isotopoic activities were determkined by alpha spectrometry, after different pre-concentration and counting sample preparation techniques., Additionally, total concentrations of uranium were determined by fluorimetry and gamma spectreometry. the folloing conclusions could be drawn from this intercomparison test: (1) The results for²³⁸U specific activity agreed with the amjority of results within 10%. Lincar correlation coefficients between the three data sets were 0.999. However, for a few samples of much higher uranium concentrations, large deviations were observed, indicating problems of, sample heterogencity. (2) For the²³⁴U/²³⁸U activity ratio data, a still closer agreement was obtained (5%), as computation of the activity ratios did not, require information on the yield of the used tracer spike (²³²U). (3) The results for²³²Th specific activities and²³⁰Th/²³⁴U activity ratios showed larger deviastions between the three laboratories (typically up to 15%, in some cases still ore). Different Th-isotopes (²²⁸Th,²³⁴Th and²²⁹Th) have been used as yield tracers. The data indicates, however, that the observed deviations are not simply a consequence of a systematic difference in the calibration of the different spikes, but, probably cased by other errors such as incomplete sample dissolution, sample heterogencity, tec. The limitations of alpha spectrometry will be discussed and an application of the developed methods shown.     

Determination of U and Th in soil and plants obtained from a high natural radiation area in China using ICP-MS and γ-counting

This study was carried out for the determination of ²³⁸U and ²³²Th concentrations in soil and various foods obtained in high natural radiation areas in China for estimating the internal radiation doses caused by these radionuclides. Knowledge of the daily dietary intakes of the nuclides through foods is essential to evaluate the internal radiation dose. Several analytical methods were evaluated for their applicability and quality assurance. The accuracy and precision of ICP-MS is considerably better for determining trace elements like U and Th in fine powder samples. The estimated annual effective dose is 0.302 μ Sv/y for ²³⁸U and 1.86 μ Sv/y for ²³²Th in the high natural radiation area, and 0.0101 μ Sv/y for ²³⁸U and 0.177 μ Sv/y for ²³²Th in the control area. Received: 25 September 1998 / Revised: 3 December 1998 / Accepted: 8 December 1998     

Effect of alteration processes on the distribution of radionuclides in uraniferous sedimentary rocks and their environmental impact, southwestern Sinai, Egypt

The contents of natural radionuclides in various types of sedimentary rocks in Um Bogma Formation and base of El Hashash Formation were determined by gamma-ray spectrometry. Three types of lower Carboniferous sedimentary rocks were investigated; sandstone (El Hashash Formation), dolostone and argillaceous sediments (Um Bogma Formation). The alteration processes are dolomitization, dedolomitization, karstification and lateritization. The specific radioactivity of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K determined in different samples, indicate that ²³⁸U and its decay products contribute primarily to the high natural radioactivity of rocks. The maximum concentration of ²³⁸U reached up to 2129.36 ppm in argillaceous sediments. The average concentrations of determined radionuclides (²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K) are 8.34 ppm, 7.88 ppm, 4.68 ppm and 0.3%, respectively in sandstone. In dolostones the average concentrations are 418.69 ppm, 808.75 ppm, 3.14 ppm and 0.29%, respectively. For argillaceous sediments are 276.88 ppm, 419.49 ppm, 11.47 ppm and 0.93%, respectively. The ²³⁸U/²²⁶Ra ratio in sandstone ranges between 0.89 and 1.25, while in dolostones and argillaceous sediments are 0.27–2.63 and 0.27–1.83, respectively. These variations in the concentrations of radioelements and their ratios are due to the action of the alteration processes affected these different sedimentary rocks in different times. Environmentally, the Ra_eq in dolostones and argillaceous sediments exceeds the permitted limits, while in the sandstone samples; it is within the permissible levels.     

Massenspektrometrische Bestimmung von ppm-Mengen Thorium in Uranerzen durch Isotopenverdünnungsanalyse

Thorium is chemically separated from uranium ores in a non-quantitative way. In one sample the isotopic ratio ²³⁰Th/²³²Th is determined in a mass spectrometer. In another sample ionium is added as indicator for the isotopic dilution; the thorium of this particular sample is also analysed in a mass spectrometer. The content of ²³⁰Th and ²³²Th is calculated from the measurements of the isotopic ratios and the amount of the ionium indicator. The results are compared with the results obtained by other methods.     

Effect of humic acid,pH and ionic strength on the sorption of Eu(III) on red earth and its solid component

A highly sensitive separation procedure has been developed to investigate uranium and thorium activities and their isotopic ratios in environmental water samples in Tokushima, Japan. Uranium and thorium isotopes in environmental water samples were simultaneously isolated from interfering elements with extraction chromatography using an Eichrom UTEVA™ resin column. After the chemical separation, activities of U and Th isotopes coprecipitated with samarium fluoride (SmF₃) were measured by α-spectrometry. It has been confirmed that uranium isotopes are isolated successfully from thorium decay chains by analyzing a test aqueous solution as a simulation of an environmental water sample. The separation procedure has been first applicable to the determination of U and Th activities and their isotopic ratios in a drinking well water named “Kurashimizu” in Tokushima City, Japan. The specific activities of ²³⁸U and ²³²Th in “Kurashimizu” were deduced to be within the upper limits of <0.31 and <0.19 mBq/l, respectively.     

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.     

Distribution and environmental impact of radionuclides in marine sediments along the Venezuelan coast

The activity concentrations of ¹³⁷Cs, ⁴⁰K, ²²⁶Ra and ²³²Th in Bq/kg from 42 marine sediment samples collected at nine sampling sites were determined in order to establish a radiological baseline along the Venezuelan coast. The radioactivity levels were determined by means of a gamma-ray spectroscopy system using a hyper-pure germanium detector in a low-background configuration. Particle size distribution and total organic matter content were also determined. Activity concentrations of ¹³⁷Cs were lower than the detection limit of the analytical technique (0.9 Bq/kg) in all studied sites. The results suggest that the variation of grain-size distribution is one of the most important factors influencing the spatial variations of ⁴⁰K, ²²⁶Ra and ²³²Th in sediments along the Venezuelan coasts. In all sampling sites, average concentrations of ⁴⁰K, ²²⁶Ra and ²³²Th were lower than the world average values. Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in coastal marine sediments along the Venezuelan coast could be considered to be low when compared with global average values, indicating that they are not apparently above of the range that might be considered normal or background. These results suggest that the studied sites do not pose any significant radiological threat to the population. The results attained in this study should be of considerable value as baseline data and background reference levels for Venezuelan coastlines.