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At least 973 records · Page 54Linked to original sources
PubMed1984

Dual isotope scintigraphy in stroke patients.

Platelet scintigraphy is a useful technique to detect atherosclerotic lesions of the neck vessels in stroke patients. The habitual one isotope technique causes false positive and false negative results due to circulating platelet-bound activity. To eliminate these confusing results we performed a dual isotope technique on 20 stroke patients. The new method consists of simultaneous injections of 111-Indium labelled blood platelets and 99mTc labelled red cells, and achieves a calculation of the ratio 111-In/99mTc. Thus the subtraction of the red cell blood flow image can render a pure thrombus formation visible. The habitual visually evaluated one isotope scintigraphy showed positive scans in 11 out of 20 patients, whereas under dual isotope scintigraphy 3 patients showed no 111-Indium excess after subtraction of the red cell image; they can thus be qualified as false positive. In the case of another patient with a visually negative image a thrombus formation could be observed after the subtraction procedure. It seems, that the dual isotope technique in platelet scintigraphy is a valuable refinement on the way to verifiable results.

Blood Platelets↗
PubMed1987

Simultaneous double-isotope autoradiographic measurement of local cerebral glucose metabolic rate and acid-base status in rat brain.

We developed a double-isotope autoradiographic method for the simultaneous measurement of the local cerebral metabolic rate for glucose (1CMRG) and index of regional acid-base status (rABI) in single brain slices using [2-14C]deoxy-D-glucose (DG) and 5,5-dimethyl-[2-14C]oxazolidine-2,4,dione (DMO). After iv isotope administration, paper chromatography separates plasma DMO from DG activity using a methanol-methylene chloride solvent system. Initial tissue autoradiograms depict regional DMO plus DG and DG metabolite distribution. After 14 days in a well-ventilated hood, 97.5 +/- 0.5% of all DMO is lost from tissue sections by sublimation, and a second autoradiogram depicts DG plus DG metabolite distribution. Retention of brain lipids does not alter beta-particle self-absorption, avoiding problems associated with isotope extraction with solvents. Autoradiograms are digitized and converted to isotope-content images. The second autoradiogram is used for 1CMRG computation. After subtracting the second regional isotope-content value from the first, the DMO content is obtained and used to compute rABI. Application of this method to normal animals yields expected values for 1CMRG and rABI. This method is amenable to whole-slice digitization and creation of functional images of 1CMRG and ABI followed by pixel-by-pixel correlations of the two variables, making this a potentially valuable tool for the investigation of the relationships between glucose metabolism and brain acid-base balance.

Acid-Base Equilibrium↗
PubMed2002

Determination of butyltin compounds in environmental samples by isotope-dilution GC-ICP-MS.

Isotope-dilution analysis in combination with GC-ICP-MS detection has been applied to the determination of butyltin species in environmental samples. Different spikes containing the isotopically labeled butyltin species have been synthesized in the laboratory after optimization of the reaction conditions. The isotopic compositions of the tin species in the different spike solutions were determined by GC-ICP-MS after derivatization by aqueous ethylation with sodium tetraethylborate. Reverse isotope-dilution analysis was used for quantitation of the spike solutions by means of natural MBT, DBT, and TBT standards. The mixed spikes were used for simultaneous analysis of MBT, DBT and TBT in the certified reference materials, PACS-2, CRM 462, and CRM 646, with satisfactory results. The excellent agreement of the different speciation results obtained by use of the different spikes is a good indicator of the precision, accuracy, and reliability which can be achieved by using isotope-dilution analysis for trace metal speciation. Application of a double spike containing (119)Sn-enriched MBT (79.7 At%), (118)Sn-enriched DBT (86.7 At%), and (119)Sn-enriched TBT (83.1 At%) also enabled evaluation of the conditions resulting in quantitative extraction of the species from the solid matrix, in combination with possible alterations depending on the different extraction procedures used (mechanical shaking, ultrasounds, and microwaves). Mathematical equations used for this purpose computed the correct species concentrations directly and, additionally, the decomposition factors (from TBT to DBT and from DBT to MBT) after precise measurement of the (119)Sn/(120)Sn and (118)Sn/(120)Sn ratios for all butyltin species by GC-ICP-MS.

Chromatography, High Pressure Liquid↗
PubMed2003

Precise isotope-ratio determination by CGC hyphenated to ICP-MCMS for speciation of trace amounts of gaseous sulfur, with SF6 as example compound.

Capillary gas chromatography coupled to an inductively coupled plasma mass spectrometer with multiple-collector detection (GC-ICP-MCMS) has been used to assess the precision and instrumental mass bias in sulfur isotope-ratio determination for the gaseous sulfur species SF6. The isotopic composition of the compound was certified by the institute for reference materials and measurements (IRMM, Belgium) and is available as PIGS 2010. Integration of the peaks (peak half-width 1.4 s) was performed using a special peak-integration method based on definition of the integration area by assessment of a uniform isotope-ratio area within the chromatographic peak. Instrumental mass bias was determined to be approximately 12% per mass unit and proved to be stable in the concentration range measured. Replicate injections of 2, 10, 20, and 30 ng (as S) SF6 diluted in argon gave precision for the 32S/34S ratio from 0.6% RSD for 2-ng injections to 0.03% RSD for 30-ng injections. The 32S/33S and 33S/34S isotope-ratio precision was better than 0.4% RSD for injections of 10 ng (as S) and higher. Detection limits were in the absolute pg range for all measured sulfur isotopes.

Journal Article↗
PubMed2005

Establishing a chromium-reactor design for measuring delta2H values of solid polyhalogenated compounds using direct elemental analysis and stable isotope ratio mass spectrometry.

2H/1H isotope ratios of polyhalogenated compounds were determined by elemental analysis and isotope ratio mass spectrometry (EA-IRMS). Initial measurements with standard EA-IRMS equipment, which used high-temperature pyrolysis to convert the organic compounds into hydrogen, did not achieve significant signals for polychlorinated pesticides and related compounds, presumably due to the formation of HCl instead of hydrogen. To reverse this problematic reaction, a chromium reactor was incorporated into the element analyzer system, which scavenged Cl, forming chromium chloride and releasing hydrogen again in the form of H2. The optimized system therefore allowed the delta2H values of polyhalogenated compounds to be determined. A quality assurance program was developed based on several parameters. (i) Each compound was analyzed using a sequence of five injections, where the first measurement was discarded. (ii) Recovery of H (when calculated relative to acetanilide) had to be >90% for all replicates in a sequence. (iii) All delta-values within a sequence had to vary by less than 10/1000. (iv) Results had to be reproducible on another day with a different sample scheme. Once this reproducibility had been established, variabilities in the delta2H values of organohalogen standards were investigated using the technique. The highest delta2H value of +75/1000 was found for o,p'-DDD, whereas the strongest depletion in deuterium was found for Melipax (-181/1000). The most important results for comparable compounds were as follows. DDT-related compounds gave delta2H values of between +59 and +75/1000 (technical DDT, o,p'- and p,p'-DDD) or in the range of approximately -1/1000, indicative of the different sources/methods of producing this compound. Four HCH isomers from the same supplier showed relatively similar hydrogen isotope distributions, whereas two lindane (gamma-HCH) standards from other sources had 39/1000 less deuterium. This difference is likely due to different purification steps during the isolation of pure lindane from the technical HCH mixture. An even greater difference was observed between the delta2H values of Toxaphene (US product dating from 1978) and Melipax (product from the former East Germany, dating from 1979), which gave delta2H values of -101/1000 and -181/1000, respectively, meaning that both products were easily distinguished via delta2H-IRMS. Fractioning of hydrogen isotopes in the atmospheric water cycle was suggested as one reason for the different values. In this theory, the water (which had different delta2H values depending on where it was taken from) was incorporated during the biosynthesis of camphene, which is the natural product used to produce both products. These results indicate that hydrogen isotope-specific analysis can be a valuable tool for tracing the origins of a compound in certain cases.

Aldrin↗
PubMed2001

Determination of uranium isotopic composition and 236U content of soil samples and hot particles using inductively coupled plasma mass spectrometry.

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 x 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 x 10(-4) and 1.4 x 10(-4), respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 microg 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/P38U) 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, alpha- and gamma-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.

Mass Spectrometry↗
PubMed2001

Isotope-ratio measurements of lead in NIST standard reference materials by multiple-collector inductively coupled plasma mass spectrometry.

The capability of a second-generation Nu Instruments multiple collector inductively coupled plasma mass spectrometer (MC-ICP-MS) has been evaluated for precise and accurate isotope-ratio determinations of lead. Essentially the mass spectrometer is a double-focusing instrument of Nier-Johnson analyzer geometry equipped with a newly designed variable-dispersion ion optical device, enabling the measured ion beams to be focused into a fixed array of Faraday collectors and an ion-counting assembly. NIST SRM Pb 981, 982, and 983 isotopic standards were used. Addition of thallium to the lead standards and subsequent simultaneous measurement of the thallium and lead isotopes enabled correction for mass discrimination, by use of the exponential correction law and 205Tl/203Tl = 2.3875. Six measurements of SRM Pb-982 furnished the results 206Pb/204Pb = 36.7326(68), 207Pb/204Pb = 17.1543(30), 208Pb/204Pb = 36.7249(69), 207Pb/206Pb = 0.46700(1), and 208Pb/206Pb = 0.99979(2); the NIST-certified values were 36.738(37), 17.159(25), 36.744(50), 0.46707(20), and 1.00016(36), respectively. Direct isotope lead analysis in silicates can be performed without any chemical separation. NIST SRM 610 glass was dissolved and introduced into the MC-ICP-MS by means of a micro concentric nebulizer. The ratios observed were in excellent agreement with previously reported data obtained by TIMS and laser ablation MC-ICP-MS, despite the high Ca/Pb concentration ratio (200/1) and the presence of many other elements at levels comparable with that of lead. Approximately 0.2 microg lead are sufficient for isotope analysis with ratio uncertainties between 240 and 530 ppm.

Journal Article↗
PubMed2001

Steady-state isotopic fractionation in branched pathways using plant uptake of NO3- as an example.

A steady-state isotopic discrimination model is developed for material transfer between a single source and two distinct sinks arising from an internal branching of the uptake pathway. Previous analyses of isotopic discrimination in multistep processes are extended to include the effects of the interacting sinks. The theory is first developed as a set of generic expressions allowing for flexibility in the definition of intermediate pools in all parts of the branched transport pathways, and then applied to a case study of nitrate uptake by plants. The isotopic composition of assimilated nitrate may be evaluated with the model for either contrasting root versus shoot assimilate pools, each with a unique isotopic signature, or as a single mean value for whole-plant nitrate reduction. The theory is further developed to indicate how isotopic measurements may be used to infer (i) efflux:influx ratios at the root plasma membrane, (ii) partitioning of assimilate capture between root and shoot reduction sites, and (iii) mixing of root and shoot assimilate pools in sink tissues due to whole-plant circulation of organic nitrogen in both xylem and phloem.

Algorithms↗
PubMed2006

Isotopic effects in the electronic spectra of tryptophan.

No influence of isotopic substitution in deuterium-substituted tryptophan on the florescence excitation spectrum has previously been found out. Here, the isotopic effects of electronic excitation of deuterium-substituted tryptophan were experimentally and theoretically analyzed for first time. It was shown a short-wave shift of the UV-absorption maximum at 220 nm corresponding to the 360 cal/mol and short-wave shift for fluorescence spectrum corresponding to the 210 cal/mol. To account for this effect, the quantum chemical calculations of the geometric and electron structure, frequencies of normal vibrations and transition energies have been performed. The isotopic effects originate from the zero-point energies of ground and excited states. It was found that isotopic shifts depend on the position of isotope in the molecule and kind of transition. So, it can be utilized in the analysis of proteins structure and complexation.

Deuterium↗
PubMed2004

Validation of a single-isotope-labeled cholesterol tracer approach for measuring human cholesterol absorption.

Cholesterol absorption is frequently determined using the plasma dual stable-isotope ratio method (PDSIRM). However, this method involves intravenous injection of stable-isotope-labeled cholesterol with simultaneous oral administration of differently labeled cholesterol, which results in high study costs and involves additional ethical considerations. The objective of the present study was to validate a simpler single-isotope method for determining cholesterol absorption against PDSIRM by using data from two previous studies. Enrichments of carbon-13 (13C and deuterium in red blood cells were analyzed by using differential isotope ratio MS. The area under the curve of 13C-enrichment in the plasma free-cholesterol pool was found to be significantly correlated with cholesterol absorption measured by using PDSIRM for study 1 (r = 0.85, P < 0.0001) and study 2 (r = 0.81, P < 0.0001). Average 13C-enrichment correlated with the area under the curve of 13C-enrichment in the plasma free cholesterol for both study 1 (r = 0.98, P < 0.0001) and study 2 (r = 1.00, P < 0.0001). Study 1 examined the efficacy and mechanisms of unesterified plant sterols and stanols on lipid profiles in hypercholesterolemic men and women, while study 2 investigated the effects of phytosterol vs. phytostanol esters on plasma lipid levels and cholesterol kinetics in hyperlipidemic men. Experimental approaches to determine cholesterol absorption were identical between the two studies. Consequently, in both studies, correlations (r = 0.88, P < 0.0001 for study 1, and r = 0.82, P < 0.0001 for study 2) were found between the average 13C-enrichment of plasma free cholesterol and cholesterol absorption measured by PDSIRM. These results suggest that a single-isotope-labeled cholesterol tracer approach can be used as a reliable noninvasive method to replace PDSIRM for examining changes in cholesterol absorption.

Absorption↗
PubMed1979

Dual-isotope separation technique for radioassay. Precision of calculated results affected by degree of separation.

The dual-isotope separation technique for radioassay is reviewed. An expression is derived describing the effect of counting errors on the precision of the calculated bound count rate in the dual-isotope technique. This mathematic model is tested in experiments using sodium iothalamate (I-125) as a marker in the Phadebas radiosorbent assay of cobalamin (Co-57). The coefficient of variation of results calculated on the basis of the dual-isotope technique is shown to be dependent on the amount of supernatant removed. The conclusion is that relatively large amounts of the supernatant must be removed before counting if the dual-isotope technique is to give acceptable results. The experimental model is proposed as a simple test of the suitability of a projected dual-isotope system.

Analysis of Variance↗
PubMed1995

Evaluation of myocardial ischemia using a rest metabolism/stress perfusion protocol with fluorine-18 deoxyglucose/technetium-99m MIBI and dual-isotope simultaneous-acquisition single-photon emission computed tomography.

OBJECTIVES: This study sought to develop a dual-isotope single-acquisition single-photon emission computed tomographic (SPECT) protocol using a multihead SPECT camera equipped with an ultra-high energy collimator to evaluate rest metabolism/stress perfusion simultaneously with fluorine-18 (F-18) deoxyglucose/technetium-99m (Tc-99m) 2-hexakis-2-methoxy-2-methylpropyl isonitrile (MIBI). BACKGROUND: The most accurate and logistic method of identifying injured but viable myocardium remains a diagnostic challenge. METHODS: Sixty-five patients were given 25 to 50 g of glucose and, after approximately 60 min, an injection of 370 MBq (10 mCi) of F-18 fluorodeoxyglucose. After a 35-min distribution phase, patients underwent exercise or pharmacologic stress followed by administration of 925 MBq (25 mCi) of Tc-99m MIBI. Five patients underwent F-18 fluorodeoxyglucose position emission tomography before dual-isotope SPECT: RESULTS: With a window of 20% for both photopeaks and a technetium-99m/fluorine-18 concentration of 3.2:1, the "spillover" from fluorine-18 into the technetium-99m window is < 6% of the total counts in the window in patients with a normal distribution of both radiopharmaceuticals. Phantom images clearly demonstrated cardiac defects measuring 2 x 1 and 2 x 0.5 cm. There was no significant difference in the images of the five patients who underwent both positron emission tomography and SPECT: Fifty-seven patients (mean [+/- SD] age 55 +/- 15 years, range 25 to 83; 38 men, 19 women) had satisfactory images and were included in the study. Twenty-one patients had normal study results; 15 had mismatched defects; 14 had matched defects; and 7 had both matched and mismatched defects. Twenty-three patients (mean age 54 +/- 6 years, range 30 to 83; 14 men, 9 women) underwent coronary angiography within 3 months of dual-isotope SPECT: There were seven normal studies, eight with mismatched defects, one with a matched defect and seven with matched and mismatched defects. When stenosis > 70% was used as the criterion for a diagnosis of coronary artery disease, dual-isotope SPECT had a sensitivity of 100%, specificity of 88%, positive predictive value of 93%, negative predictive value of 100% and an accuracy of 96%. CONCLUSIONS: Dual-isotope SPECT may provide an alternative, accurate, cost-effective method to nitrogen-13 ammonia/F-18 fluorodeoxyglucose positron emission tomography or thallium-201 reinjection for identifying injured or dysfunctional but viable myocardium.

Coronary Angiography↗
PubMed2004

High-throughput quantification of phosphatidylcholine and sphingomyelin by electrospray ionization tandem mass spectrometry coupled with isotope correction algorithm.

The choline head group containing phosphatidylcholine (PC) and sphingomyelin (SPM) are major eukaryotic lipid components playing an important role in forming membrane microdomains and serve as precursor of signaling molecules. Both lipids can be monitored by positive ion mode electrospray tandem mass spectrometry using a parent ion scan of m/z 184. Although PC species appear at even m/z and SPM species at odd m/z, there may be a significant overlap of their isotopes. In order to separate PC and SPM species, an isotope correction algorithm was established, which utilizes calculated isotope percentages to correct the measured peak intensities for their isotopic overlap. We could demonstrate that this approach was applicable to correct the isotope overlap resulting from spiked PC and SPM species. Quantification was achieved by addition of different PC and SPM species prior to lipid extraction. The developed assay showed a precision, detection limit and robustness sufficient for routine analysis. Furthermore, an analysis time of only 1.3 min combined with automated data analysis using self-programmed Excel Macros allows high-throughput analysis. In summary, this assay may be a valuable tool for detailed lipid analysis of PC and SPM species in a variety of sample materials.

Algorithms↗
PubMed2005

The influence of isotope and prostate volume on urinary morbidity after prostate brachytherapy.

PURPOSE: To evaluate the influence of isotope and prostate size on International Prostate Symptom Score (IPSS) normalization, catheter dependency, and the need for surgical intervention secondary to bladder outlet obstruction after prostate brachytherapy. METHODS AND MATERIALS: Between January 1998 and June 2003, 976 consecutive patients underwent brachytherapy for clinical stage T1b-T3a (2002 American Joint Committee on Cancer) prostate cancer. Seven hundred eighty-nine (80.8%) were implanted with 103Pd and 187 (19.2%) with 125I. The median follow-up was 41.2 months. Patients were stratified into size cohorts < or = 25 cm3, 25.1-35 cm3, 35.1-45 cm3, and >45 cm3. Four hundred eighteen patients (42.8%) received androgen deprivation therapy (ADT). Four hundred eighty-six patients (49.7%) received supplemental external-beam radiation therapy (XRT). In all patients, an alpha blocker was initiated before implantation and continued at least until the IPSS returned to baseline. IPSS resolution was defined as a return to within one point of baseline. The median number of IPSS determinations per patient was 21. Clinical, treatment, and dosimetric parameters evaluated included patient age, pretreatment PSA, Gleason score, clinical T stage, percent positive biopsies, preimplant IPSS, ultrasound volume, planning volume, isotope, V(100/150/200), D(90), urethral dose (average and maximum), supplemental XRT, ADT, and the duration of ADT (< or = 6 months vs. >6 months). Catheter dependency and the need for postsurgical intervention were also evaluated. RESULTS: For both isotopes and all prostate size cohorts, IPSS peaked 1 month after implantation and returned to baseline at a mean of 1.9 months. Stratification of prostate size cohorts by isotope demonstrated no significant differences in prolonged catheter dependency (> or = 5 days), IPSS resolution, or postimplant surgical intervention. In Cox regression analysis, IPSS normalization was best predicted by preimplant IPSS, XRT, and any need for a catheter after brachytherapy. Catheter dependency correlated with prostate size and ADT, whereas the need for surgical intervention was most closely related to any catheter dependency, maximum urethral dose, ADT, and maximum IPSS increase. CONCLUSIONS: Regardless of prostate size, isotope did not impact IPSS resolution, catheter dependency, or the need for postbrachytherapy surgical intervention. Although prostate size did predict for short-term (<5 days) catheter dependency, it did not influence IPSS resolution or the need for surgical intervention.

Aged↗
PubMed2005

Zinc stable isotope fractionation during its adsorption on oxides and hydroxides.

Adsorption of Zn on goethite, hematite, birnessite, pyrolusite, corundum, and gibbsite was studied using a batch adsorption technique as a function of pH, zinc concentration in solution, and time of exposure. Adsorption from 0.01 M NaNO3 solutions undersaturated with respect to zinc (hydr)oxide at 3 MeOZn+ complexes, where Me=Fe, Mn, and Al, was used to describe the dependence of adsorption equilibria on aqueous solution composition in a wide range of pH and Zn concentration. The logarithms of surface stability constant for Zn interaction with metal oxy(hydr)oxides (>MeOH0+Zn2+-->MeOZn+) vary from -2.5 to 0.5. They are higher for oxy(hydr)oxides than for anhydrous oxides. Stable isotopes of zinc in several filtrates were measured using an ICP-MS Neptune multicollector which made it possible, for the first time, to assess the degree of isotopic fractionation between 66Zn and 64Zn during zinc adsorption on mineral surfaces. The isotopic offset between aqueous solution and mineral surfaces (Delta(66/64)Zn(soln/solid)=delta((66/64)Zn)(solution)-delta((66/64)Zn)(surface)) was found to be weakly dependent on percentage of adsorbed metal and equals 0.20+/-0.03, 0.17+/-0.06, -0.10+/-0.03, -0.10+/-0.09, and -0.13+/-0.12 per thousand for goethite, birnessite, pyrolusite, corundum, and Al(OH)3. For hematite, Delta(66/64)Zn varies from -0.61+/-0.10 per thousand at pH 5.5 to -0.02+/-0.09 per thousand at 5.8 MeOZn(H2O)(n) complexes (available literature data on X-ray absorption spectroscopy). Apparently, the fine structure of surface complexes and the position and bond strength for second neighbors of zinc are likely to control its isotopic fractionation during adsorption on mineral surfaces. Our results strongly suggest that inorganic processes controlling zinc isotope adsorption on soil and sediment minerals should be of second-order importance compared to biological factors.

Journal Article↗
PubMed2006

Determination of extremely low (236)U/(238)U isotope ratios in environmental samples by sector-field inductively coupled plasma mass spectrometry using high-efficiency sample introduction.

A method by inductively coupled plasma mass spectrometry (ICP-MS) was developed which allows the measurement of (236)U at concentration ranges down to 3 x 10(-14)g g(-1) and extremely low (236)U/(238)U isotope ratios in soil samples of 10(-7). By using the high-efficiency solution introduction system APEX in connection with a sector-field ICP-MS a sensitivity of more than 5,000 counts fg(-1) uranium was achieved. The use of an aerosol desolvating unit reduced the formation rate of uranium hydride ions UH(+)/U(+) down to a level of 10(-6). An abundance sensitivity of 3 x 10(-7) was observed for (236)U/(238)U isotope ratio measurements at mass resolution 4000. The detection limit for (236)U and the lowest detectable (236)U/(238)U isotope ratio were improved by more than two orders of magnitude compared with corresponding values by alpha spectrometry. Determination of uranium in soil samples collected in the vicinity of Chernobyl nuclear power plant (NPP) resulted in that the (236)U/(238)U isotope ratio is a much more sensitive and accurate marker for environmental contamination by spent uranium in comparison to the (235)U/(238)U isotope ratio. The ICP-MS technique allowed for the first time detection of irradiated uranium in soil samples even at distances more than 200 km to the north of Chernobyl NPP (Mogilev region). The concentration of (236)U in the upper 0-10 cm soil layers varied from 2 x 10(-9)g g(-1) within radioactive spots close to the Chernobyl NPP to 3 x 10(-13)g g(-1) on a sampling site located by >200 km from Chernobyl.

Environmental Pollution↗
PubMed2006

Isotopic signature of atmospheric xenon released from light water reactors.

A global monitoring system for atmospheric xenon radioactivity is being established as part of the International Monitoring System to verify compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The isotopic activity ratios of (135)Xe, (133m)Xe, (133)Xe and (131m)Xe are of interest for distinguishing nuclear explosion sources from civilian releases. Simulations of light water reactor (LWR) fuel burn-up through three operational reactor power cycles are conducted to explore the possible xenon isotopic signature of nuclear reactor releases under different operational conditions. It is studied how ratio changes are related to various parameters including the neutron flux, uranium enrichment and fuel burn-up. Further, the impact of diffusion and mixing on the isotopic activity ratio variability are explored. The simulations are validated with reported reactor emissions. In addition, activity ratios are calculated for xenon isotopes released from nuclear explosions and these are compared to the reactor ratios in order to determine whether the discrimination of explosion releases from reactor effluents is possible based on isotopic activity ratios.

Air Pollutants, Radioactive↗
PubMed2006

239+240Pu concentration and isotope ratio (240Pu/239Pu) in aerosols during high dust (Yellow Sand) period, Korea.

Concentration and isotope ratio of Pu were analyzed for aerosols collected at Anmyeondo located in the western coast of Korea using multiple collector inductively coupled plasma mass spectrometer equipped with desolvated micro-concentric nebulizer. Aerosols were collected from June 2001 to April 2002 using high volume air sampler. The samples consist of high dust samples (Yellow Sand), and also low dust samples; maximum Al concentration was 74.2 microg/m(3) and minimum was 0.17 microg/m(3). Pu was concentrated using 0.1 ml TEVA resin columns after conc. HNO(3) extraction. Isotope dilution using (242)Pu spike and mass bias correction using (233)U and (236)U mixed solution enabled the quantification of Pu and measurement of isotope ratio simultaneously. The contribution of (238)U from both spikes and samples was minimized by careful chemical separation and optimization of spike concentration. The (238)U(1)H and tail contribution on (239)Pu peak were about 0.75 x 10(-5) and 1 x 10(-5) of (238)U intensity, respectively, and they were corrected from (239)Pu using externally determined ((238)U(1)H + tailing)/(238)U ratio and (238)U measurement during acquisition. The detection limits of this analytical procedure were 0.61 fg/ml and 0.56 fg/ml for (239)Pu and (240)Pu, respectively (4 nBq/m(3) and 12 nBq/m(3) for (239)Pu and (240)Pu, respectively). The precision of isotope ratio measurement was better than 2% for larger quantity than 20 fg of (239)Pu. In spring, maximum concentration of 0.580 microBq/m(3) for (239)Pu and 0.404 microBq/m(3) for (240)Pu was observed when Al concentration was maximum, so called as Yellow Sand event. Pu concentrations in aerosols are well correlated with Al, a tracer of soil dust. The ratios of Pu/Al were 0.0082 (microBq/microg) and 0.0055 (microBq/microg) for (239)Pu/Al and (240)Pu/Al, respectively. Isotope ratios of Pu ((240)Pu/(239)Pu) in Yellow Sand samples show 0.191+/-0.014 close to those of global fallout. These facts indicate that Yellow Sand plays an important role in the behavior of Pu in the environment like other concomitant metals such as Al, Fe etc.

Aerosols↗