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1.
A new technique to measure 234U/238U and 236U/238U isotope ratios for individual particles in environmental samples was developed, which was a combination of particle isolation under scanning electron microscope (SEM) and secondary ion mass spectrometry (SIMS). The technique was verified by measuring 234U/238U and 236U/238U isotope ratios in individual particles in a simulated environmental sample containing uranium standard (NBL CRM U010) and Pb metal particles. When the uranium particles were not isolated, the relative deviations of the measured isotope ratios from the reference values increased with increasing the signal intensity ratio of 208Pb to 238U, which was due to the molecular ion interferences by the Pb particles co-existing in the sputtered area. By the isolation of individual uranium particles, the interferences were eliminated and the measured isotope ratios were in good agreement with the reference values. The maximum relative deviations among 20 particles were 8.9% for 234U/238U and 13.1% for 236U/238U isotope ratios, respectively. The technique was also successfully applied to the analysis of a real swipe sample containing various kinds of elements.  相似文献   

2.
The capability of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of uranium isotope ratios in individual particles was determined. For this purpose, we developed an experimental procedure including single particle transfer with a manipulator, chemical dissolution and isotope ratio analysis, and applied to the analysis of individual uranium particles in certified reference materials (NBL CRM U050 and U350). As the result, the 235U/238U isotope ratio for the particle with the diameter between 0.5 and 3.9 μm was successfully determined with the deviation from the certified ratio within 1.8%. The relative standard deviation (R.S.D.) of the 235U/238U isotope ratio was within 4.2%. Although the analysis of 234U/238U and 236U/238U isotope ratios gave the results with inferior precision, the R.S.D. within 20% was possible for the measurement of the particle with the diameter more than 2.1 μm. The developed procedure was successfully applied to the analysis of a simulated environmental sample prepared from a mixture of indoor dust (NIST SRM 2583) and uranium particles (NBL CRM U050, U350 and U950a). From the results, the proposed procedure was found to be an alternative analytical tool for nuclear safeguards.  相似文献   

3.
Uranium concentration in groundwater reflect both redox conditions and uranium content in host rock. In the present study an attempt has been made to study the uranium concentration and activity ratios of uranium isotopes to present the geochemical conditions of the groundwater in Malwa region of Punjab state, India and the reason for high uranium levels and variation of activity ratios from secular equilibrium conditions. Uranium concentration in groundwater samples was found to be in the range of 13.9 ± 1.2 to 172.8 ± 12.3 μg/l with an average value of 72.9 μg/l which is higher than the national and international guideline values. On the basis of uranium concentration, the groundwater of the study region may be classified as oxidized aquifer on normal uranium content strata (20 %) or oxidized aquifer on enhanced uranium content strata (80 %). The 238U, 235U and 234U isotopic concentration in groundwater samples was found to be in the range of 89.2–1534.5, 4.4–68.5, and 76.4–1386.2 mBq/l, respectively. Activity ratios of 234U/238U varies from 0.94 to 1.85 with a mean value of 1.11 which is close to unity that shows secular equilibrium condition. High value of 234U isotope than 238U may be due to alpha recoil phenomenon. The plot of AR of 234U/238U against the total uranium content in log scale reveals that the groundwaters of the study region either belongs to stable accumulation or normal oxidized aquifer.  相似文献   

4.
The smear samples of the penetrator were analyzed for the determination of the uranium composition. The obtained relative composition (m/m) of uranium isotopes in all the smear samples is in the range of 99.76-99.78% for 238U, 0.000659-0.000696% for 234U, 0.213-0.234% for 235U, and 0.00274-0.00328% for 236U, showing characteristics of depleted uranium (DU). The uranium concentrations in Kosovo soil and water samples as well as biological samples were investigated. It was found that the uranium concentrations in the Kosovo soil samples are in the range of 11.3-2.26·105 Bq·kg-1 for 238U, 10.3-3.01·104 Bq·kg-1 for 234U, 0.60-3251 Bq·kg-1 for 235U, and £0.019-1309 Bq·kg-1 for 236U. The obtained activity ratios are in the range of 0.112-1.086 for 234U/238U, 0.0123-0.1144 for 235U/238U, and 0-0.0078 for 236U/238U, indicating the presence of DU in about 77% of the surface soil samples. At a specific site, the DU inventory in the surface soil is about 140 mg·cm-2, which is 1.68·106 times higher as the estimated mean DU dispersion rate in the region. The uranium concentrations in Kosovo lichen, mushroom, bark, etc., are in the range of 1.97-4.06·104 Bq·kg-1 for 238U, 0.48-5158 Bq·kg-1 for 234U, 0.032-617 Bq·kg-1 for 235U, and £0.019-235 Bq·kg-1 for 236U with mean activity ratios of 0.325±0.0223 for 234U/238U, of 0.0238±0.0122 for 235U/238U, and 0.0034±0.0028 for +U/238U, indicating the presence of DU in the entire sample. On the contrary, the uranium concentrations in Kosovo water samples are low, compared with the water samples collected in central Italy, indicating the presence of negligible amount of DU. The uranium isotopes in Kosovo waters do not constitute a risk of health at the present time. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
The determination of isotope ratios in individual uranium particles is very important for nuclear safeguards. In this work, accelerator mass spectrometry (AMS), thermal ionization mass spectrometry (TIMS), and secondary ion mass spectrometry (SIMS) were applied to isotope ratio analysis of individual uranium particles and compared in terms of background, measurement accuracy, and efficiency. Several individual uranium particles (1–7 μm) from certified reference materials were used as samples. The results show that the average values of blank counting rate of 235U for AMS, FT-TIMS (FT: fission track), SEM-TIMS (SEM: scanning electron microscope), and SIMS were 7.3, 7.8, 2.7 and 2.2 cps, respectively. The relative error of 234U/235U and 234U/236U isotope ratios of the particles from U200 for AMS were within 10% and 20%, whereas the results of FT-TIMS and SIMS were within 5% and 10%, respectively. The relative error and external precision of 234U/238U and 235U/238U of the particles from U850 for the method of AMS, SEM-TIMS, and SIMS were within 10% and 5%, respectively. For 236U/238U, the average values of the relative error and external precision measured by AMS were within 5%, which measured by SEM-TIMS and SIMS were all within 10%. AMS has advantages in measuring 236U/238U. The measurement time of AMS and SEM-TIMS was shorter than that of FT-TIMS and longer than that of SIMS. It is considered that AMS and SEM-TIMS have a certain development prospect, and it is necessary to research deeply.  相似文献   

6.
The surface leaching of the labile component of uranium has been carried out in estuarine sediments of Zuari river in Goa. The measurements of alpha activities of238U,235U and234U in the leachates indicated a remarkable anomaly between the activities of238U and234U. The activity ratios of234U/238U in these leachates have been found to be in the range of 1.10 to 1.14. However, the activity ratios of235U/238U have been found to be 0.045 which is close to that in natural uranium. It has also been observed that the anomaly between238U and234U exists only on the surface organic layers of the backwater sediments of the Zuari river.  相似文献   

7.
The effect of sediment size, pH, temperature and conductivity on the transfer of uranium from sediment to water has been studied. The uranium concentration and the234U/238U,235U/238U activity ratios were measured in water, sediments and suspended matter sampled from Jucar River, using low level alpha-spectrometry. Distribution factors were obtained from these measurements. A more detailed sampling was done in the neighbourhood of the Cofrentes Nuclear Plant (Valencia, Spain). Total uranium activity,234U/238U activity ratio and distribution factors for234U and238U were found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes.  相似文献   

8.
Samples of coastal marine sediments of the East Coast of India were leached with a saturated solution of ammonium carbonate for the extraction of uranium from the sediment particle surface without attacking the mineral core of the particles. All the sediment samples were found to exhibit a234U/238U activity ratio in the range of 1.07 to 1.14. On removal of surface organic matter, the234U/238U activity ratio is close to 1.00, indicating that the anomaly between238U and234U exists only on the labile surface layer. However, no such variations are observed in235U/238U activity ratios. These ratios are close to 0.045 which is the same as that of natural uranium.  相似文献   

9.
D. Alamelu 《Talanta》2009,77(3):991-994
A correlation has been developed for the determination of 235U/238U atom ratio in uranium samples using liquid scintillation counting (LSC). The 235U/238U atom ratio determined by thermal ionization mass spectrometry (TIMS) was correlated to the ratio of (i) α-count rate and (ii) Cerenkov count rate due to 234mPa in the sample; both measured by LSC. This correlation is linear over the range of 235U/238U atom ratio encountered in the nuclear fuel samples, i.e. the low enriched uranium (LEU) samples with 235U < 20 atom%. The methodology based on this correlation will be useful for the quick determination and verification of 235U/238U atom ratios in fuel samples using cost effective technique of LSC.  相似文献   

10.
The determination of uranium isotope ratios in individual particles is of great importance for nuclear safeguards. In the present study, an analytical technique by inductively coupled plasma mass spectrometry (ICP-MS) with a desolvation sample introduction system was applied to isotope ratio analysis of individual uranium particles. In ICP-MS analysis of individual uranium particles with diameters ranging from 0.6 to 4.2 μm in a standard reference material (NBL CRM U050), the use of the desolvation system for sample introduction improved the precision of 234U/238U and 236U/238U isotope ratios. The performance of ICP-MS with desolvation was compared with that of a conventionally used method, i.e., secondary ion mass spectrometry (SIMS). The analysis of test swipe samples taken at nuclear facilities implied that the performance of ICP-MS with desolvation was superior to that of SIMS in a viewpoint of accuracy, because the problems of agglomeration of uranium particles and molecular ion interferences by other elements could be avoided. These results indicated that ICP-MS with desolvation has an enough ability to become an effective tool for nuclear safeguards.  相似文献   

11.
A round-robin for uranium isotopic analysis in two solutions with different concentrations prepared and certified by the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) was organized by CETAMA, a division of the Commissariat à l’énergie Atomique (CEA: French Atomic Energy Commission Fourteen laboratories took part in the program using twenty-five different instruments (ICP-QMS, ICP-SFMS and TIMS). For each solution and each isotopic ratio, a statistical analysis based on standard ISO 5725 was carried out to calculate the mean, the repeatability and reproducibility standard deviations, the z-score and zeta-score, the bias with respect to the target values, and to compare their precision. The mean measurement results for the 234U/238U and 235U/238U isotopic ratios show no significant biases compared with the target values, whatever is the analytical technique. The results were much less satisfactory for the 236U/238U isotopic ratio, for which only the laboratories specialized in traces analyses and/or precise isotopic analyses submitted results in good agreement with the target values. A detailed discussion is given in this article.  相似文献   

12.
The determination of isotopes of uranium by alpha spectrometry in different environmental components (sediments, soil, water, plants and phosphogypsum) is presented and discussed in this paper. The alpha spectrometry is a very convenient and good technique for activity concentration of natural uranium isotopes (234U, 235U, 238U) in environmental samples and provides the most accurate determination of isotopic activity ratios between 234U and 238U. The analysis were provided information about possible sources of high concentrations of uranium in the examined sites determined by anthropogenic sources. The calculation of values 234U/238U in all analyzed samples was applied to identifying natural or anthropogenic uranium origin. Activity concentration of uranium isotopes in analyzed environmental samples shows that measurement of uranium levels is of great importance for environmental and safety assessment especially in contaminated areas (phosphogypsum waste heap).  相似文献   

13.
We employed femtosecond Laser Ablation Multicollector Inductively Coupled Mass Spectrometry for the determination of uranium isotope ratios in a series of standard reference material glasses (NIST 610, 612, 614, and 616). The uranium in this series of SRM glasses is a combination of isotopically natural uranium in the materials used to make the glass matrix and isotopically depleted uranium added to increase the uranium elemental concentration across the series. Results for NIST 610 are in excellent agreement with literature values. However, other than atom percent 235U, little information is available for the remaining glasses. We present atom percent and isotope ratios for 234U, 235U, 236U, and 238U for all four glasses. Our results show deviations from the certificate values for the atom percent 235U, indicating the need for further examination of the uranium isotopes in NIST 610-616.  相似文献   

14.
As a result of the accident at the Chernobyl nuclear power plant (NPP) the environment was contaminated with spent nuclear fuel. The 236U isotope was used in this study to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP. Nuclear track radiography was applied for the identification and extraction of hot radioactive particles from soil samples. A rapid and sensitive analytical procedure was developed for uranium isotopic ratio measurement in environmental samples based on double-focusing inductively coupled plasma mass spectrometry (DF–ICP–MS) with a MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN). The performance of the DF–ICP–MS with a quartz DIHEN and plasma shielded torch was studied. Overall detection efficiencies of 4×10–4 and 10–3 counts per atom were achieved for 238U in DF–ICP–QMS with the MicroMist nebulizer and DIHEN, respectively. The rate of formation of uranium hydride ions UH+/U+ was 1.2×10–4 and 1.4×10–4, respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 μg L–1 NBS U-020 standard solution was 0.11% (238U/235U) and 1.4% (236U/238U) using a MicroMist nebulizer and 0.25% (235U/238U) and 1.9% (236U/238U) using a DIHEN. The isotopic composition of all investigated Chernobyl soil samples differed from those of natural uranium; i.e. in these samples the 236U/238U ratio ranged from 10–5 to 10–3. Results obtained with ICP–MS, α- and γ-spectrometry showed differences in the migration properties of spent uranium, plutonium, and americium. The isotopic ratio of uranium was also measured in hot particles extracted from soil samples.  相似文献   

15.
The main results of chemical and radiochemical characterization and fractionation of depleted uranium in soils contaminated during the Balkan conflict in 1999 are presented in the paper. Alpha-spectrometric analysis of used depleted uranium material has shown the presence of man-made radioisotopes 236U, 237Np, and 239, 240Pu traces. The fractionation in different soil types was examined by the application of a modified Tessier’s five-step sequential chemical extraction procedure, specifically selective to certain physical/chemical associations. After ion-exchange-based radiochemical separation of uranium, depleted uranium is distinguished from naturally occurring uranium in extracts on the basis of the isotopic activity ratios 234U/238U and 235U/238U and particular substrates for recently present uranium material in soils are indicated. The text was submitted by the authors in English.  相似文献   

16.
The precision in measurement of trace level uranium isotopic ratio, i.e., 236U/238U or 234U/238U, on single Faraday detector with narrow dynamic range is very hard to achieve. this is mainly due to the narrow dynamic range of a single detector systems. A significant improvement in mass spectrometric determination of 236U/238U ratio has been achieved by employing an alternate method using a single Faraday detector of narrow dynamic range. The method makes use of the precise measurements of the 236U/234U ratio, 234U/235U ratio and 235U/238U ratio, which are used to calculate the 236U/238U ratio using the equation 236U/238U=236U/234234U/235235U/238U. Despite the fact that correlation of the data tends to increase the uncertainty in the result, our results show a significant improvement, i.e., more than 8 times better precision in measuring the 236U/238U ratio with this method (σ=3.98×10−08) as compared to direct measurement of 236U/238U (σ=3.104×10−07). The method widens the applicability of the single collector system with narrow dynamic range and it will potentially be helpful to improve the precision in the case of the static multi-collector system also. The objective of the present study was to compare the results of the same sample analyzed with the present alternate method and the direct method for precision.  相似文献   

17.
Uranium (U) and plutonium (Pu) isotopes in coral soils, contaminated by nuclear weapons testing in the northern Marshall Islands, were isolated by ion-exchange chromatography and analyzed by mass spectrometry. The soil samples were spiked with 233U and 242Pu tracers, dissolved in minerals acids, and U and Pu isotopes isolated and purified on commercially available ion-exchange columns. The ion-exchange technique employed a TEVA® column coupled to a UTEVA® column. U and Pu isotope fractions were then further isolated using separate elution schemes, and the purified fractions containing U and Pu isotopes analyzed sequentially using multi-collector inductively coupled plasma mass spectrometer (MCICP-MS). High precision measurements of 234U/235U, 238U/235U, 236U/235U, and 240Pu/239Pu in soil samples were attained using the described methodology and instrumentation, and provide a basis for conducting more detailed assessments of the behavior and transfer of uranium and plutonium in the environment.  相似文献   

18.
The uranium concentration and the234U/238U,235U/238U activity ratios were studied in water samples from Jucar River, using low-level -spectrometry. The effects of pH, temperature and salinity were considered and more detailed sampling was done in the neighbourhood of Cofrentes Nuclear Plant (Valencia, Spain). Changes were observed in the uranium concentration with the salinity and the234U/238U activity ratio was found to vary with pH. Leaching and dilution, which depend on pH and salinity, are the probable mechanisms for these changes in the concentration of uranium and the activity ratios.  相似文献   

19.
Approximately 100 freshwater samples were collected in Ukraine, Russia, and Belorussia with regard to the Chernobyl accident. Thorium and uranium were determined by both quantitative and semiquantitative analysis modes of inductively coupled plasma mass spectrometry (ICP-MS). Thorium-232 was detected in only a few samples. Uranium concentrations ranged from non-detectable to 1,000ng/ml. Mean and median concentrations of238U were found to be 30.7±139 and 0.7 ng/ml, respectively. The isotope ratio of234U/238U ranged from 4.6·10–5 to 4.4·10–4. Mean ratio of235U/238U was 0.00721±0.00006 (n=27).  相似文献   

20.
An analytical method for the ultratrace and isotopic analysis of uranium in radioactive waste samples using a double-focusing sector field ICP mass spectrometer is described. In high-purity water a detection limit for uranium in the lowest fg/mL range has been achieved. Under optimum experimental conditions (235U/238U ≈ 1), the precision in 235U/238U isotopic ratio determinations has been determined as 0.07% RSD. With the isotopic standard U-020 (235U/238U = 0.0208) a precision of 0.23% RSD at the 100 pg/mL level using ultrasonic nebulization has been achieved. With 234U/238U isotopic ratios of down to 10–5, the values obtained by double-focusing sector field ICP-MS and alpha spectrometry were in agreement. Received: 27 February 1997 / Revised: 10 Juni 1997 / Accepted: 12 June 1997  相似文献   

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