- Geospatial analysis and assessment of 226Ra, 235U, 232Th, 137Cs, and 40K at Anzali wetland, north of Iran. [Journal Article]
- EMEnviron Monit Assess 2019 May 22; 191(6):390
- Achieving better monitoring and radiation risk assessment is among the main issues in environmental studies. In this regard, natural radioactivity measurements in sediments can provide useful informa…
Achieving better monitoring and radiation risk assessment is among the main issues in environmental studies. In this regard, natural radioactivity measurements in sediments can provide useful information about the environmental transport mechanism and about the sources of radionuclides. Anzali wetland, as the study area of this research, is located on the southwestern shore of the Caspian Sea with rapidly changing ecosystems. Because of its strategic location, increasing pollution levels, decreasing water table, and increasing sediment discharge from rivers, Anzali wetland has a unique significance in terms of studying its radioactivity from sediment and soil samples. The average 226Ra, 235U, 232Th, 137Cs, and 40K values for 33 sediment and soil samples were 24.66, 3.72, 31.94, 11.66, and 506.38 Bq kg-1, respectively. Variography analyses revealed a spatial structure with minimum/maximum variance equal to 3/8 from 135°/45° azimuth direction. In addition, the fractal geometry indicates values higher than 3.7, 24.5, 30, 25, and 475 Bq kg-1 as anomalous values for 235U, 226Ra, 232Th, 137Cs, and 40K using Kriging estimated data with a search radius of 5000 m, respectively. Compared with the average values published by UNSCEAR (2008) for earth's crust average and compared with the values for the southern areas of Iran (Oman Sea), the estimated average and anomalous data for a pollutant at Anzali wetland do not exceed the reference data. The higher values in the samples of this study could be related to specific environmental problems such as industrial wastewater from about 30 polluted factories transported by 10 major rivers. Agricultural wastes, such as herbicides, pesticides, and fertilizers from rice fields, and being a tourist attraction zone at sea beach are the other most possible pollution sources in the study area.
- Dispersion pattern of 226Ra and 235U using the ERICA Tool in the coastal mining area, Ierissos Gulf, Greece. [Journal Article]
- ARAppl Radiat Isot 2019; 145:198-204
- Natural radionuclides, present in mining materials, can exhibit elevated values, thus it is of great interest to study their dispersion in mining areas. Radionuclide spatial variations were determine…
Natural radionuclides, present in mining materials, can exhibit elevated values, thus it is of great interest to study their dispersion in mining areas. Radionuclide spatial variations were determined in coastal surface sediments near the mining area of Ierissos Gulf in northern Greece. 226Ra and 235U measured concentrations were compared with the estimations of ERICA Tool, the dispersion patterns were derived and the affected region around the load-out pier area was calculated to be approximately 21 km2.
- Measurement of uranium distribution coefficient and 235U/238U ratio in soils affected by Fukushima dai-ichi nuclear power plant accident. [Journal Article]
- JEJ Environ Radioact 2019; 198:36-42
- Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted radioactive contamination in soil due to deposition of mainly radiocesium as well as many long-lived radionuclides surrounding a large …
Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted radioactive contamination in soil due to deposition of mainly radiocesium as well as many long-lived radionuclides surrounding a large area around FDNPP. Depending upon environmental conditions, radionuclides in soil can be mobilized in aquatic systems. Therefore, the fate and transfer of these radionuclides in the soil water system is very important for radiation protection and dose assessment. In the present study, soil and water samples were collected from contaminated areas around FDNPP. Inductively coupled plasma mass spectrometry (ICP-MS) is used for total uranium concentration. Emphasis has been given on isotope ratio measurement of 235U/238U ratio using thermal ionization mass spectrometry (TIMS) that gives us the idea about its contamination during accident. For the migration behavior, its distribution coefficient (Kd) has been determined using laboratory batch method. Chemical characterization of soil with respect to different parameters has been carried out. The effect of these soil parameters on distribution coefficient of uranium has been studied in order to explain the radionuclide mobility in this particular area. The distribution coefficient values for uranium are found to vary from 30 to 36000 L/kg. A large variation in the distribution coefficient values shows the retention or mobility of uranium is highly dependent on soil characteristics in the particular area. This variation is explained with respect to soil pH, Fe, Mn, CaCO3 and organic content. There is a very good correlation of uranium Kd obtained with Fe content. There is no enrichment of 235U has been noticed in the studied area.
- Measurement of the 231Pa/235U ratio for the age determination of uranium materials. [Journal Article]
- JRJ Radioanal Nucl Chem 2018; 318(3):1565-1571
- The paper describes the age (production date) determination of uranium reference materials using the 231Pa/235U ratio. Direct addition of 237Np in secular equilibrium with its 233Pa daughter was chos…
The paper describes the age (production date) determination of uranium reference materials using the 231Pa/235U ratio. Direct addition of 237Np in secular equilibrium with its 233Pa daughter was chosen instead of the regular milking of 237Np to avoid possible loss of Pa. Sample preparation consists of a fast, one-step procedure. The developed method using ICP-MS for the measurement of 231Pa is more precise than alpha spectrometry and is applicable for freshly produced low-enriched uranium materials. The measured ages are in good agreement with the reported production dates, thus the 231Pa/235U chronometer can be applied for validation of 230Th/234U in nuclear forensics and safeguards.
- Direct, uncorrected, molecule-free analysis of 236U from uranium-bearing particles with NAUTILUS: a new kind of mass spectrometer. [Journal Article]
- AAnalyst 2018 Nov 05; 143(22):5364-5371
- We demonstrate use of the Naval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS) at the U.S. Naval Research Laboratory (NRL) to measure 236U directly from uranium-bearing particles …
We demonstrate use of the Naval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS) at the U.S. Naval Research Laboratory (NRL) to measure 236U directly from uranium-bearing particles free from molecular isobaric interferences. Particles with 235U enrichments in the range of 0.32% to 3.28% and 236U enrichments from no enrichment to 0.015% provided by the International Atomic Energy Agency (IAEA) were analyzed directly using the NAUTILUS. We report the experimental data here without correcting for molecular hydrides and/or applying any other background subtractions. The results from all samples agreed with the certified values within standard error save for the 236U composition of the IRMM 023, which suffered from a combination of insufficient particle sizes and sub-μmol mol-1 236U concentrations. We were able, however, to directly measure as low as three μmol mol-1 of 236U in individual particles regardless of the 235U concentration. Our results are comparable with Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS) and serve as baseline for a more comprehensive comparison between LG-SIMS and the NAUTILUS in the future. Moreover, we demonstrate the ability of the NAUTILUS to generate raster ion images with the same ease as traditional LG-SIMS instruments. By combining our ability to measure 236U directly with raster ion imaging, we were able to detect a low intensity, small uranium-bearing particle in the presence of high molecular backgrounds for a non-ideal sample. This discovery could lead to more targeted and, therefore, less time intensive particle screening methodologies.
- Thermal neutron scattering cross sections of 238U and 235U in the γ phase. [Journal Article]
- JPJ Phys Condens Matter 2018 Oct 17; 30(41):415401
- The development of metallic, low-enrichment uranium fuels requires accurate prediction of their neutron transport properties and reactivity parameters, which in turn require thermal neutron scatterin…
The development of metallic, low-enrichment uranium fuels requires accurate prediction of their neutron transport properties and reactivity parameters, which in turn require thermal neutron scattering data. Accurate prediction of thermal neutron scattering data, including thermal cross sections, requires knowledge of the phonon scattering properties of the medium, but such matrix binding effects in next-generation fuels such as U-Mo, U-Zr, and U-Si are typically neglected because these effects are often difficult to measure or calculate. Using molecular dynamics simulations with previously published interatomic potentials, we calculate the phonon dispersion relations and phonon densities of states for 235U and 238U in the α and γ phases. The performance of these potentials was evaluated using published ab initio simulation data and inelastic neutron scattering data. The phonon densities of states obtained by each potential were then utilized to calculate the thermal neutron scattering cross sections of 235U and 238U at 1113 K using the NJOY program. The resulting thermal neutron scattering cross sections are assessed by comparison to data obtained from available experimental densities of states. The cross sections generated show how the addition of binding effects decreases the cross section by up to a factor of six over the free-atom model. A definite effect on reactivity is also demonstrated by the use of these thermal libraries on a simple core model. As a consequence, the cross sections generated in this work provide a better description of the true cross section than the free-atom data currently available. We also discuss the sensitivity of the thermal scattering cross sections to the phonon density of states.
- DETERMINATION AND DOSE CONTRIBUTION OF URANIUM ISOTOPES AND 210Po ACTIVITY CONCENTRATIONS OF NATURAL SPRING WATERS IN THE PROVINCE OF GRANADA, SPAIN. [Journal Article]
- RPRadiat Prot Dosimetry 2018 Nov 01; 181(4):350-359
- The activity concentrations of alpha-emitters comprising isotopes of uranium (238, 234, 235U) and polonium (210Po) were measured using alpha-particle spectrometry in natural spring waters in the prov…
The activity concentrations of alpha-emitters comprising isotopes of uranium (238, 234, 235U) and polonium (210Po) were measured using alpha-particle spectrometry in natural spring waters in the province of Granada, Spain. These water are consumed by the population of the zone who live in villages. This is almost half of the population of the whole region. Mean values of activity concentrations found are 42.61 ± 2.66; 49.55 ± 3.03; 1.64 ± 0.28 and 1.74 ± 0.15 mBq L-1 for 238U, 234U, 235U and 210Po, respectively. Finally, the radiological impact of the analysed waters has been determined, in terms of the estimation of the committed annual effective dose due to the ingestion of the water. The assessment has been carried out for five age groups with the aim to cover all the population. The calculated annual effective doses are observed to be below the prescribed dose limit of 100 μSv y-1 recommended by WHO.
- Field Application of 238U/235U Measurements To Detect Reoxidation and Mobilization of U(IV). [Journal Article]
- ESEnviron Sci Technol 2018 Mar 20; 52(6):3422-3430
- Biostimulation to induce reduction of soluble U(VI) to relatively immobile U(IV) is an effective strategy for decreasing aqueous U(VI) concentrations in contaminated groundwater systems. If oxidation…
Biostimulation to induce reduction of soluble U(VI) to relatively immobile U(IV) is an effective strategy for decreasing aqueous U(VI) concentrations in contaminated groundwater systems. If oxidation of U(IV) occurs following the biostimulation phase, U(VI) concentrations increase, challenging the long-term effectiveness of this technique. However, detecting U(IV) oxidation through dissolved U concentrations alone can prove difficult in locations with few groundwater wells to track the addition of U to a mass of groundwater. We propose the 238U/235U ratio of aqueous U as an independent, reliable tracer of U(IV) remobilization via oxidation or mobilization of colloids. Reduction of U(VI) produces 238U-enriched U(IV), whereas remobilization of solid U(IV) should not induce isotopic fractionation. The incorporation of remobilized U(IV) with a high 238U/235U ratio into the aqueous U(VI) pool produces an increase in 238U/235U of aqueous U(VI). During several injections of nitrate to induce U(IV) oxidation, 238U/235U consistently increased, suggesting 238U/235U is broadly applicable for detecting mobilization of U(IV).
- On similarity of various reactor spectra and 235U prompt fission neutron spectrum. [Journal Article]
- ARAppl Radiat Isot 2018; 135:83-91
- A well-defined neutron spectrum is an essential tool not only for calibration and testing of neutron detectors used in dosimetry and spectroscopy but also for validation and verification of evaluated…
A well-defined neutron spectrum is an essential tool not only for calibration and testing of neutron detectors used in dosimetry and spectroscopy but also for validation and verification of evaluated cross sections. A new evaluation of thermal-neutron induced 235U PFNS was performed by the International Atomic Energy Agency (IAEA) in the CIELO (Collaborative International Evaluated Library Organisation Project) project; new measurements of Spectral Averaged Cross sections averaged in the evaluated spectrum are to be obtained. In general, a neutron spectrum in the core is not identical to the pure fission one because fission neutrons undergo many scattering reactions, but it can be shown that PFNS and reactor spectra become undistinguishable from a certain energy boundary. This limit is important for experiments, because when the studied reaction threshold is over this limit, the spectral averaged cross sections in PFNS can be derived from the measured reactions in the reactor core. The evaluation of the neutron spectrum measurements in three different thermal-reactor cores shows that this lower limit is around the energy of 5.5 - 6 MeV. Above this energy the reactor spectra becomes identical with the 235U PFNS. IAEA CIELO PFNS is within 5% of the measured PFNS from 10 to 14 MeV in a LR-0 reactor, while ENDF/B-VII evaluated PFNS underestimated measured neutron spectra.
New Search Next
- Measurement of absolute γ-ray emission probabilities in the decay of 235U. [Journal Article]
- ARAppl Radiat Isot 2018; 132:72-78
- Accurate measurements were performed of the photon emission probabilities following the α decay of 235U to 231Th. Sources of highly enriched 235U were characterised in terms of isotopic composition b…
Accurate measurements were performed of the photon emission probabilities following the α decay of 235U to 231Th. Sources of highly enriched 235U were characterised in terms of isotopic composition by mass spectrometry and their activities were standardised by means of alpha-particle counting at a low defined solid angle. The standardised sources were subsequently measured by high-resolution γ-ray spectrometry with calibrated high-purity germanium detectors to determine the photon emission probabilities. Four laboratories participated in this work and reported emission probabilities for 33 γ-ray lines. Most of them agree with previously published evaluated data. In addition, new values are proposed for γ-lines which have been measured only once in the past.