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.     

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.     

Measurement of uranium in total diet samples: Daily intake for Japanese

Diet samples were collected by a duplicate portion study of Japanese adults in two districts, a newly-rising town and an established seaside village, of Ishikawa Prefecture, which faces the Sea of Japan. Uranium concentrations in a total of 80 diet samples were determined by -spectrometry after chemical separation. No marked differences between the two districts were found regarding characteristics of food consumption in thirteen categories and in daily intake of²³⁸U per person. The daily intake of²³⁸U per person ranged from 1.1 to 40 mBq with a geometric mean value of 9.6±2.1 mBq. The²³⁴U/²³⁸U activity ratios ranged from 0.7–1.5, with most being from 1.0–1.2. The internal dose estimation system (IDES) was completed with Japanese physical parameters and other parameters of ICRP Publication 30, and then the annaul effective dose equivalent was estimated as 3·10^–7 Sv for²³⁸U in a Japanese adult.     

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.     

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.     

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.     

Development of new centrifuges for fast solvent extraction of transactinide elements

Inductively coupled plasma-mass spectrometry (ICP-MS) was used to concurrently determine multiple long-lived (t_1/2>10⁴ y) actinide isotopes in soil leachates. Ultrasonic nebulization was found to maximize instrument sensitivity. Instrument detection limits for actinides in solution ranged from 50 mBq L^–1 (²³⁹Pu) to 2Bq L^–1 (²³⁵U). Hydride adducts of²³²Th and²³⁸U interfered with the determinations of²³³U and²³⁹Pu; thus, extraction chromatography was used to concentrate the analytes and separate uranium from the other actinides in advance of mass spectrometric determination. Alpha spectrometric determinations of²³⁰Th,²³⁹Pu, and the²³⁴U/²³⁸U activity ratio in soil leachates compared well with ICP-MS determinations; however, there were some small systematic differences (ca. 10%) between ICP-MS and -spectrometric determinations of²³⁴U and²³⁸U activities. These differences were attributed to the use of different isotope dilution spikes for ICP-MS and -spectrometry.     

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).     

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.     

Multi-element analysis of 18 food groups using semi-quantitative ICP-MS

Fifteen radionuclides and stable elements in 18 food groups, which have been obtained by a market basket method, were determined by semiquantitative ICP-MS. Strontium, Cs,²³²Th, and²³⁸U were also determined by quantitative analytical ICP-MS or ICP-AES. For Sr,²³²Th, and²³⁸U, results of the semi-quantitative ICP-MS and the quantitative approaches were found to be in a good agreement, within ±10%. The other eleven elements (Li, V, Cr, Mn, Co, Ni, Cu, Rb, Mo, Cd, and Ba were determined with in 30% errors at the sub-ppb (ng/ml) level. More elements could be measured by the semi-quantitative mode if concentrations were at least at the sub-ppb level.     

The leachability of some natural and man-made radionuclides from soil and sediments on acid attack

A radiotracer study was made of the leachability of some natural and man-made radionuclides from soils and sediments subjected to attack by various acid mixtures. Particular attention was paid to the nuclides²³⁸U,²³²Th, Pa (as²³³Pa) and Np (as²³⁹Np), since for these neutron activation can be used to study recoveries and/or to induce in situ radionuclides in samples. Thus conventional NAA allowed determination of total²³⁸U and²³²Th instrumentally, and also enabled analysis of leachates and residues by radiochemical or instrumental NAA. Activation of these nuclides produced samples endogenously labelled with²³³Pa and²³⁹Np whose behaviour on acid dissolution/leaching could be examined. Furthermore, comparison of neutron irradiated and non-irradiated samples allowed us to investigate the possibility of increased leachability induced by nuclear recoil reactions; however, this effect was negligible. We also investigated the acid leaching of americium adsorbed on the surface of sediment. In general, unsatisfactory leaching recoveries were found for²³³Pa,²³⁹Np and²³²Th for most materials, indicating the need for total dissolution procedures.     

Measurement of the radioactivity of238U,232Th,226Ra,137Cs and40K in soil using direct Ge(Li) γ-ray spectrometry

Radioactivity of the nuclides²³⁸U(²³⁵U),²³²Th,²²⁶Ra,¹³⁷Cs and⁴⁰K was measured in soil by direct -ray spectrometry using Ge(Li) detector. Relative laboratory method was used. Soil was dired, powdered, sieved and put into hemetically sealed container. CCRMP certified reference materials and compounds of the above nuclides mixed with fine quartz sand were used as references. Five and four -lines were used for the determination of²³²Th and²²⁶Ra, respectively, to obtain more accurate results. The most significant interferences, caused by the limited energy resolution of the detector, were resolved. In the case of ordinary soils, using one day duration of measurement and 1 kg mass of soil,²³²Th,²²⁶Ra and⁴⁰K can be determined with less than 10% relative random error. Elevated concentrations of²³⁸U(²³⁵U) and²²⁶Ra were observed in soil samples collected around a coal-fired power plant in Ajka town, Hungary.     

Alpha-emitting radionuclide contents in food samples as related to the Chernobyl accident

As a preliminary survey to establish intake of -emitting nuclides, in particular^239,240Pu, from a daily diet for inhabitants living near the Chernobyl reactor site, some kinds of food samples including total diet samples were collected in the Chernobyl (Ukraine) area and in the Ibaraki prefecture (Japan). Plutonium-239 and 240 were determined together with naturally occurring -emitters²²⁶Ra and U isotopes (²³⁴U,²³⁵U and²³⁸U) by -spectrometry after chemical separation. In most of the samples studied,^239,240Pu was less than the detectable amount, but in some mushrooms from the Ukraine it was found to be 41.6 mBq kg^–1 (wet mass) with a high activity ratio(0.58±0.08) of²³⁸Pu/^239,240Pu, indicating that nearly 100% of the^239,240Pu was attributable to the accident. Concentrations of²²⁶Ra and²³⁸U varied largely, depending on the samples. The measured activity ratios of²³⁵U/²³⁸U for some samples showed the isotopic composition of natural uranium.     

Anomalously high 234U/238U activity ratios of Tatsunokuchi hot spring waters, Ishikawa Prefecture, Japan

Uranium concentration and the ²³⁴U/²³⁸U activity ratio have been measured for the Tatsunokuchi hot spring waters of Ishikawa Prefecture in Japan, collected periodically over a long period (1977-2000). The concentration of ²³⁸U varied drastically between 0.045 and 1.02 mBq/l (a factor of about 20), while the ²³⁴U concentration was almost unchanged, ranging from 2.30 to 3.07 mBq/l. Resultant ²³⁴U/²³⁸U activity ratios showed a wide range from 2.7 to 51. Equilibrium calculation by using the geochemical code showed that U for one end-member representing low uranium contents and very high ²³⁴U/²³⁸U ratios was expected to exist as UO₂(CO₃)₂ ^2-. By using the U isotopic and ¹⁴C dating methods, the age of this water was roughly estimated to be in the range of 10⁴-10⁵ years.     

Analysis of natural radionuclides from uranium and thorium series in briney groundwaters

Analytical procedures for measuring various radionuclides in the²³⁸U and²³²Th chains in briney waters are described. Using methods such as mass spectrometry, and alpha, beta and gamma spectrometry, the desired measurement sensitivity required for each of the radionuclides is achieved.²³³U,²²⁸Th,²⁰⁸Po,²¹²Pb, and¹³³Ba are used as tracers for chemical yield recoveries. Typical precision of the results range from 5–20%.     

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.     

238U and 232 Th concentrations in various potable waters in Morocco and resulting annual equivalent doses for the population

Summary The ²³⁸U and ²³² Th concentrations were measured in various potable water samples collected from various cities in Morocco using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs). The measured ²³⁸U and ²³² Th concentrations ranged from 0.37±0.02 to 13.60±0.97 mBq ^. l^-1 and 0.33±0.02 to 7.10±0.49 mBq ^. l^-1, respectively. Alpha-activities due to annual ²³⁸U and ²³² Th intakes were assessed in various compartments of the human body of adult members of the Moroccan population using ICRP biokinetic models. The equivalent doses due to annual intakes of ²³⁸U and ²³² Th were evaluated. The influence of the target tissue mass and the activities of ²³⁸U and ²³² Th on the annual committed equivalent doses in the compartments of the human body was investigated.     

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.     

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.     

Investigate the capability of INAA absolute method to determine the concentrations of 238U and 232Th in rock samples

This work aimed to study the capability of INAA absolute method in determining the elemental concentration of ²³⁸U and ²³²Th in the rock samples. The INAA absolute method was implemented in PUSPATI TRIGA Mark II research reactor, Malaysian Nuclear Agency (NM). The accuracy of INAA absolute method was performed by analyzing the IAEA certified reference material (CRM) Soil-7. The analytical results showed the deviations between experimental and certified values were mostly less than 10 % with Z-score in most cases less than 1. In general, the results of analysed CRM Soil-7 show a good agreement between certified and experimental results which mean that the INAA absolute method can be used accurately for elemental analysis of uranium and thorium in various types of samples. The concentration of ²³⁸U and ²³²Th ranged from 1.77 to 24.25 and 0.88 to 95.50 ppm respectively. The highest value of ²³⁸U and ²³²Th was recorded for granite rock sample G17 of ²³⁸U and sample G9 of ²³²Th, whereas the lower value was 1.77 ppm of ²³⁸U recorded in sandstone rock and 0.88 ppm of ²³²Th for gabbro. Moreover, a comparison of the ²³⁸U and ²³²Th results obtained by the INAA absolute method shows an acceptable level of consistency with those obtained by the INAA relative method.