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1.
Inductively coupled plasma-mass spectrometry (ICP-MS) was used to concurrently determine multiple long-lived (t1/2>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.  相似文献   

2.
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.  相似文献   

3.
Samples of natural and manufactures building materials collected around Lusaka have been analyzed for natural radionuclides using -spectrometry. A simple comparison of the specific radioactivities of primordial radionuclides in these materials to the world averages for soil (25 Bq kg–1 238U, 25 Bg kg–1 232Th, 370 Bq kg–1 40K and 89 Bq kg–1 Raeq) shows that, of the nine types of samples analyzed, only burnt clay bricks (for238U,232Th and40K), cement roofing tiles (for238U), building and river sands (for232Th and40K) have greater activities than does soil. Radiological evaluation of specific radioactivities in these materials indicates that all materials meet the external -ray dose limitation of 1.5 mSv y–1, that is, all samples have a radium equivalent activity of less than 370 Bq kg–1.  相似文献   

4.
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.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
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.  相似文献   

8.
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.  相似文献   

9.
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.  相似文献   

10.
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.  相似文献   

11.
As a preliminary survey to establish intake of -emitting nuclides, in particular239,240Pu, 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 the239,240Pu 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.  相似文献   

12.
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 of137mBa 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.  相似文献   

13.
Thorium-232 and238U contents in four food groups were measured by inductively coupled plasma mass spectrometry (ICP-MS). Daily intakes of232Th and238U for Japanese were estimated to 2.22 mBq and 15.5 mBq per person, respectively. Furthermore, preliminary estimations were made for the effects of imported foods on internal exposures for Japanese.  相似文献   

14.
The relationship of the activity ratios (ARs) of U/Th-series nuclides and associated factors (pH, Eh, and the concentrations of Cl- and SO4 2-) in the hot spring area of Taipei were determined. The contents of U and Th in water decreased with increasing pH. The 234U/238U ARs have been ascribed to alpha recoil and selective leaching of 234U, while the 234U/238U disequilibrium was not significant with regard to the statistical error. Variations of 230Th/234U ARs can be attributed to the different chemical properties of 230Th and 234U. The disequilibrium of 226Ra/230Th can be ascribed to the complexation of thorium with Cl- and SO4 2-, and to the co-precipitation of radium with sulfates. The disequilibrium of228Th/232Th can be due to the co-precipitation of 228Ra with (Ba,Pb)SO4 and to the migration of 228Th from the sediment into the water.  相似文献   

15.
Measurements of some selected radionuclides were carried out in rain waters collected from Ibaraki Prefecture, Japan, following the nuclear accident at Tomsk-7, Russian Federation, in April 1993. The concentrations obtained for artificial radionuclides were90Sr1.8 mBq l–1,137Cs0.1 Bq l–1,131I0.1 Bq l–1 and129I4 Bq l–1. Uranium (238U) concentrations in rainfalls in April 1993 were 6.3–39 ng l–1. These data were compared to control values obtained previously and there was no appreciable influence on the radioactivity levels in Japan after the Tomsk-7 accident. Since only limited data on the concentrations of129I and uranium in rain water are available, these new analytical results contribute to understanding the background levels for these nuclides.  相似文献   

16.
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.  相似文献   

17.
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.  相似文献   

18.
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.  相似文献   

19.
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.  相似文献   

20.
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.  相似文献   

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