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.     

Concentration of232Th,230Th and228Th in various tissues of Japanese subjects

The concentration of²³²Th,²³⁰Th and²²⁸Th in various human tissues of Japanese subjects obtained at autopsies are reported. The tissue samples were weighed, spiked with²³⁴Th tracer and ashed by acid. The solution was dried on a hot-plate. Separation of thorium radionuclides was accomplished through cation-exchange resin chromatography and electrodeposition. The concentrations of thorium isotopes were measured by -spectrometry. Thorium-232 and²³⁰Th concentrations were found to be highest in lung, followed by bone. The maximum concentration of²²⁸Th was in bone. The lowest concentrations of thorium isotopes were in muscle.     

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.     

The determination of radium-226 and radium-228 in soils and plants,using radium-225 as a yield tracer

Recovery of²²⁶Ra in analysis is determined using²²⁵Ra separated by anion exchange from²²⁹Th and²³³U. Radium is coprecipitated with barium, and purified by ion exchange.²²⁶Ra and²¹⁷At (decay product of²²⁵Ra) are measured by α-spectrometry.²²⁸Ra is determined both by β-counting²²⁸Ac and²²⁵Ac separated from²²⁸Ra and²²⁵Ra, and by α-counting its daughters after the decay of²²⁵Ra. Sources for α-spectrometry are prepared by electrodeposition (molecular plating).     

Message to the participants of the conference

The activity of²³²Th and its daughters in Th-based gas sockets is required for health risk assessment. By absolute measurement of the²²⁸Ac- and²¹²Pb/²⁰⁸Tl-activities, the total activity of the sockets can be assessed. It is governed by²²⁸Ra and²²⁸Th and the product age.     

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.     

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.     

Radioanalytical methods for the accurate determination of227Ac and228Th in irradiated226Ra targets

Alpha spectrometry is proposed for the quantitative analysis of²²⁷Ac and²²⁸Th in irradiated²²⁶Ra targets. The chemical separation and the radiochemical determination is described.     

Contribution to the simultaneous determination of228Ra and226Ra by using 3M's EMPORETM radium rad disks

New method for simultaneous determination of²²⁸Ra and²²⁶Ra by using 3M's EMPORE^TM Radium Rad Disks in water has been developed. Both radionuclides²²⁶Ra and²²⁸Ra were counted through their daughter products,²²⁶Ra by conventional radon emanation techniques and²²⁸Ra through its daughter²²⁸Ac by using a proportional counter. Different molarity of diammonium hydrogen citrate were used for elution of²²⁸Ac and²²⁶Ra from EMPORE^TM Radium Rad Disks. 79% of²²⁸Ac was eluted in 10 ml of 0.0003M diammonium hydrogen citrate. The recovery of²²⁶Ra was 99% by using 40 ml of 0.2M diammonium hydrogen citrate adjusted by ammonium to pH 7.8.     

Determination of Th and U in bone ash by ICP-ion source mass spectrometry

The feasibility of ICP-ion source mass spectrometry (ICP-MS) for the determination of²³²Th and²³⁸U in bone ash was studied. Bone ash samples were further decomposed with concentrated nitric acid under pressure in PTF crucibles. The resultant solution was diluted and subjected directly to the measurement with an ICP mass spectrometer. The effects of diluting and removing matrix elements on ICP-MS measurements of these nuclides were studied. The accuracy of the determinations was evaluated with the measurement of NBS Human Lung (SRM 4351) which was originally certified for alpha activities of²³²Th and²³⁸U.     

Th isotope measurements of femtogram quantities for U-series dating using multi ion counting (MIC) MC-ICPMS

Results of Th isotope measurements on Harwell Uraninite (HU) solution aliquots and carbonates such as corals and speleothems using multi ion counter (MIC) procedures are presented. A multi ion counter array available for the ThermoFinnigan Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS) is used for simultaneous measurements of ²³⁰Th and ²²⁹Th ion beams. A static collection of low-level ion beams improves the efficiency of isotope measurements which in turn reduces the required sample size and measurement time. The static measurement also circumvents problems with ion beam intensity fluctuations often observed with a plasma source. Instrumental bias corrections are based on a sample bracketing in-house Th standard solution. The accuracy and precision of the MIC array procedures for ²³⁰Th/²²⁹Th measurements are investigated by comparison to a MC-ICPMS peak jump procedure using just a single ion counting channel. The results show that similar precisions for ²³⁰Th/²²⁹Th measurements can be achieved using the MIC procedure with less than half total ²³⁰Th consumed compared to a peak jump routine. Thus, the MIC setup allows to use less than half the sample sizes for ²³⁰Th/U dating of carbonates compared to peak jump methods enabling higher spatial resolution sampling.     

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.     

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.     

The microenvironment of iron in (Ba,Ca)(Fe,Co)O3−δ catalyst system: A Mössbauer study

Undisturbed, non-fertilized woodland soil (“loamy sandy soil” type) from 1 m below surface was dry and wet sieved. Sieving fractions of <10–1000 μm were analyzed for total alpha-activity. Thorium and uranium contents were determined by alpha-spectrometry after radiochemical separation. Soluble and insoluble parts of thorium and uranium were determined in the sieved fractions indicating that the isotope distribution in soil correlates with the particle size distribution: The smaller the size fraction the higher the isotope content. Isotope ratios of²²⁸Th/²³²Th, and²³⁴U/²³⁸U are discussed.     

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 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.     

Alpha-decay from the 3.5 eV isomer of 229Th

The alpha-decay of a low energy isomer of ²²⁹Th at about 3.5 eV was sought by producing it through the (g,n) reaction on a ²³⁰Th target. Thorium isotopes in the reaction products were isolated and purified by anion exchange chromatography in a concentrated nitric acid medium to remove lanthanides fission products. The thorium fraction was further purified by samarium fluoride coprecipitation and the precipitate was mounted as a source for a-spectroscopy. Decaying a-signals were observed in the energy region that was expected for ^229mTh, i.e., between 4.83 and 5.08 MeV. The half-life of the decaying component was determined from repeated experiments to be 13.9±3 hours.     

Determination of plutonium and americium in environmental samples and assessment of thorium in bone samples from normal and high background areas

The procedures developed and standardised for estimation of ultra trace quantities of Pu and Am in environmental samples involve matrix dependent sample preparation, preconcentration of the nuclides by coprecipitation on iron hydroxide and or bismuth phosphate, ion exchange, electrodeposition and counting by alpha spectrometry. Isotopic analysis of Th in chicken bone using oxalate precipitation, ion exchange, electrodeposition and alpha spectrometry has indicated higher build up of²²⁸Th in chicken bone from monazite areas possibly from metabolized²²⁸Ra.     

Simple collection and direct alpha-spectrometric determination of214Pb and214Bi in natural water

A rapid method has been developed for the de termination of²¹⁴Pb and²¹⁴Bi in natural waters by alpha-spectrometric measurement of²¹⁴Po. Well water was filtered on a membrane filter impregnated with manganese oxide and followed by direct alpha-spectrometric analysis. A prominent alpha peak was assigned to²¹⁴Po, which should be supported by the longer lived parents²¹⁴Pb and²¹⁴Bi. The activity ratios between²¹⁴Pb and²¹⁴Bi adsorbed on the filter were determined by using the change of activity of²¹⁴Po as a function of counting period after the filtration. The adsorbed yield of²¹⁴Pb was also determined from the growth of the alpha-peak due to²¹⁰Po from a²¹⁰Pb tracer added in the original water. The results indicated that the amount of²¹⁴Pb was in radioactive non-equilibrium state with the Rn-222 dissolved, while the activity ratios of²¹⁴Bi/²¹⁴Pb showed on increasing tendency with the storage period of the water.