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.     

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.     

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.     

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.     

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.     

A study on thorium levels in human femur bones

The incorporation of naturally occurring thorium isotopes in human femur bones was studied by analyzing 28 bone samples. The results show that the activity concentrations of ²³²Th and ²³⁰Th are in the range of the blank values resulting in an upper limit of theirs activity concentrations in human bones. The presence of ²²⁸Th can be attributed, on the basis of model calculations, to the radioactive decay of deposited ²²⁸Ra. We conclude that thorium is not detectably incorporated into human bones.     

A method for the simultaneous estimation of228Th and229Th

A simple method is reported in this paper to estimate²²⁹Th in the presence of²²⁸Th. The total activity of²²⁹Th and²²⁸Th was determined by following the alpha activity growth (using a liquid scintillation counter and proportional counter) of purified thorium samples. The activity ratio of²²⁹Th/²²⁸Th was determined by alpha spectrometry. From the initial total activity and ratio, disintegration rates of²²⁹Th and²²⁸Th were calculated. The values obtained for the activities have a precision better than ±2%.     

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.     

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.     

Separation of Ra and Th from rock matrices for alpha-spectrometry

Dating rocks using²²⁶Ra/²³⁰Th isochrons demands radiochemical purification of radium and thorium. This paper presents an improved method. Rocks are solubilised by nitric/nydrofluoric digestion followed by dissolution of insoluble fluorides by boric/nitric acids, and Th is extracted by passing the 8M nitric solution through an anion column in nitrate form. The eluant contains Ra and Ba which are precipitated as sulphate and redissolved in alkaline EDTA. Complete separation of Ba and Ra from sulphate is on an AG 1×8 anion column in EDTA form, which was found better than the chloride form. The Ba+Ra is separated on an AG 50W×8 cation column, and uses CDTA as an eluant for Ba. Careful pH control is essential. Ra elutes later with EDTA or 4M HCl and is precipitated with 125 g barium as sulphate to yield a source suitable for -spectrometry, or further treated to electroplate the Ra. The yield tracers used are²²⁸Th and²²⁴Ra. Because the sample contains natural²²⁴Ra a correction must be applied, calculated from the amount of natural²³²Th in the Th spectrum. Th may be precipitated with 100 g of ferric iron and gives a spectrometry-quality source, but further purification and electrodeposition was found to be preferable. Variations on the method for the case of analysis of calcium-rich fish otoliths are described.     

Ion-exchange separation of uranium,thorium and plutonium isotopes from environmental samples

Radioisotopes of uranium, thorium and plutonium in water, soil and fertilizer samples, have been chemically separated and determined by alpha-spectrometry method. Radiochemical procedure involving ion-exchange, enabled to determine these isotopes in very low concentrations (under 50 Bq/g).²³²U,²²⁹Th and²³⁸Pu were used as a tracers for radiochemical yield recoveries (up to 90%). Thin layer sources have been obtained by electrodeposition.     

A new method for the determination of radium-228, thorium-228, and radium-224 in groundwaters via thoron (radon-220)

Current techniques for determining low levels of dissolved thorium involve chemical separations, generally by coprecipitation with a carrier cation, purification by ion exchange procedures, electroplating and, finally, alpha counting by alpha spectrometry. Similarly, measurements of low²²⁸Ra and²²⁴Ra activities requires concentration, by coprecipitation with barium sulfate, followed by gamma counting. An improved method for determining radium and thorium from the²³²Th decay series has been developed which measures the activity of²²⁰Rn as an assay of its parents. Although some ingrowth corrections and minor separation procedures for Th are required, the results to date show that the dynamic counting of²²⁰Rn via de-emanation and alpha counting by the alpha-scintillation method is a preferable approach for determining these radium and thorium isotopes accurately and efficiently. The method for lower limit detection depends on the emanation rate, which depends on purge-gas flow rate and sample volume analyzed. Using 50-cc and 1000-cc bubblers, and maximum effective purge gas flow rate, a lower limit of detection of 0.4 and 0.06 pCi/L²²⁰Rn can be obtained, respectively.     

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.     

Rapid collection of iron hydroxide for determination of Th isotopes in seawater

This work introduces a novel method of recovery of iron hydroxide using a DIAION CR-20 chelating resin column to determine Th isotopes in seawater with a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). Thorium isotopes in seawater were co-precipitated with iron hydroxide, and this precipitate was sent to chelating resin column. Ferric ions in the iron hydroxide were bonded to functional groups of the chelating resin directly, resulting in a pH increase of the effluent by release of hydroxide ion from the iron hydroxide. The co-precipitated thorium isotopes were quantitatively collected within the column, which indicated that thorium was retained on the iron hydroxide remaining on the chelating column. The chelating column quantitatively collected ²³²Th with iron hydroxide in seawater at flow rates of 20–25 mL min⁻¹. Based on this flow rate, a 5 L sample was processed within 3–4 h. The >20 h aging of iron hydroxide tends to reduce the recovery of ²³²Th. The rapid collection method was successfully applied to the determination of ²³⁰Th and ²³²Th in open-ocean seawater samples.     

Determination of alpha-emitting isotopes of uranium and thorium in vegetables and excreta

A radiochemical procedure for the determination of alpha-emitting isotopes of uranium and thorium in vegetables and excreta has been optimized, involving sample dissolution, separation by ionic exchange resin, electrodeposition and alpha-spectroscopy. Uranium and thorium isotopes were determined separately to prevent interference of ²²⁸Th from ²³²U tracer with ²²⁸Th from natural series of 232Th. This procedure was applied to faeces from people living in the Poços de Caldas plateau, a high natural radioactivity region of Brazil, and vegetables from the Laboratory of Environmental Monitoring (EML/DOE). Results show a chemical recovery of 80–95% for uranium and 46–72% for thorium.     

Interpretation of thorium bioassay data

This study is a comparison between bioassay data of thorium-exposed workers from two different facilities. The first of these facilities is a monazite sand extraction plant. Isotopic equilibrium between²³²Th and²²⁸Th was not observed in excreta samples of these workers. The second facility is a gas mantle factory. An isotopic equilibrium between²³²Th and²²⁸Th was observed in excreta samples. Whole body counter measurements have indicated a very low intake of thorium through inhalation. As the concentration of thorium in feces was very high we concluded that the main pathway of entrance of the nuclide was ingestion, mainly via contamination through dirty hands.The comparison between the bioassay results of workers from the two facilities shows that the lack of Th isotopic equilibrium observed in the excretion from the workers at the monazite sand plant possibly occurred due to an additional Th intake by ingestion of contaminated fresh food. This is presumably because²²⁸Ra is more efficiently taken up from the soil by plants, in comparison to²²⁸Th or²³²Th, and subsequently,²²⁸Th grows in from its immediate parent,²²⁸Ra.     

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.     

Distribution of137Cs,40K,238U and232Th in soils from Northern Venezuela

More than one hundred undisturbed soil samples from Northern Venezuela and the islands of Margarita and Los Roques have been analyzed for¹³⁷Cs,⁴⁰K,²³⁸U and²³²Th by -ray spectroscopy. The specimens were taken from between 5–10 cm below the earth's surface. Thus, they are valid not only for the¹³⁷Cs deposition studies but also for the estimation of the natural -ray dose from primordial radionuclides that form the terrestrial component. The concentration of⁴⁰K was directly determined from its 1461 keV -ray, while those of¹³⁷Cs,²³⁸U and²³²Th were performed using a -ray from one of their daughter radionuclides: the 661 keV -ray of^137mBa for¹³⁷Cs, the 1760 keV -ray of²¹⁴Bi for²³⁸U and the 2620 keV -ray of²⁰⁸Tl for²³²Th. Finally, the concentration values were compared with those of global estimates.     

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