Natural 238U Research Articles

Natural and artificial radioactive pollution in sediment and soil samples of the Bosphorus, Istanbul.

This study focused on the determination of natural (238U, 232Th, and 40K) and artificial (137Cs) radionuclide concentrations both in 55 sediment samples collected from various depths in the Bosphorus and 5 soil samples from the coastline of the Bosphorus, Istanbul, using gamma-ray spectrometry with an HPGe detector. The mean activity concentrations of natural 238U, 232Th, and 40K and anthropogenic 137Cs were determined to be 11.41 ± 0.21 Bq kg-1, 6.87 ± 0.16 Bq kg-1, 369.61 ± 3.41 Bq kg-1, and 6.54 ± 0.11 Bq kg-1, respectively, in the sediment samples. The average activity concentrations of 238U, 232Th, 40K, and 137Cs radionuclides in the soil samples were also measured to be 11.65 ± 0.18 Bq kg-1, 9.55 ± 0.15 Bq kg-1, 369.43 ± 3.09 Bq kg-1, and 4.57 ± 0.09 Bq kg-1, respectively. Radiological contour maps based on the activity concentrations of natural and artificial radionuclides in the sediment samples for the Bosphorus, Istanbul, were created. The total annual effective doses due to soil samples were calculated to be 34.58 μSv y-1.

Reconstructing the chronology of the natural and anthropogenic uranium isotopic signals in a marine sediment core from Beppu Bay, Japan

The long-lived U isotopes, 233U and 236U, have been used increasingly in recent years as marine circulation tracers and for identifying sources of uranium contamination in the environment. The sedimentation histories of these two U isotopes in combination with natural 238U were reconstructed for an anoxic sediment core collected from Beppu Bay, Japan, in the western North Pacific Ocean showing good time resolution (less than 2.6 y/sample). The 233U/236U atom ratio showed a prominent peak of (3.20 ± 0.30) × 10−2 around 1957 which can be attributed to the input from atmospheric nuclear weapons tests including thermonuclear tests conducting in the Equatorial Pacific. The integrated 233U/236U ratio of (1.64 ± 0.08) × 10−2 for the sediment was found to be in relatively good agreement with the representative ratio published for global fallout (∼1.4 × 10−2). A prominent increase in the authigenic ratio of 233U/238Ua,s in the leached fraction (1.39 ± 0.11 × 10−11) and the bulk digestion (1.36 ± 0.10 × 10−11) was also observed around 1957. This reflects the input supply of 233U to the seawater which is known to have a relatively constant 238U content. The authigenic 236U/238Ua,s ratio (0.18 ± 0.02 × 10−9) obtained for 1921 increased from the early 1950's to a maximum of (6.59 ± 0.60) × 10−9 around 1962. The variation in this ratio represents well the introduction history of U into the surface environment without site-specific U contamination and the time profile is also consistent with the 137Cs signature. This work thus provides a benchmark for the long-term use of the isotopic U composition as an input parameter for seawater circulation tracers and as a chronological marker for anoxic sediments and sedimentary rocks. Especially the 233U/236U ratio may serve as a key-marker for the new geological age Anthropocene.

INTERNAL EXPOSURE FROM INDOOR RADON, THORON AND THEIR PROGENY IN RESIDENCE AROUND HIGH BACKGROUND RADIATION AREA, PHANG NGA PROVINCE, THAILAND.

A passive integrating discriminative radon-thoron monitor (Raduet) and a radon-thoron progeny monitor with a solid-state nuclear tracking detector were used for estimating indoor radon, thoron and their progeny concentrations in residential areas around the old mines of southern Thailand. Exposure to high background radiation levels from natural 238U and 232Th in the tin mine areas or active fault areas may increase the risk of lung cancer in the respiratory system when considering the health effects of the surrounding inhabitants. In this study, radon thoron and their progeny concentrations from inhalation in the study site have been assessed in dose at volunteer houses to confirm radiation effects. The annual effective doses due to inhalation of radon-thoron, radon progeny and thoron progeny using the ICRP latest dose conversion factors were estimated to be 3.0-4.6, 2.5-3.7 and 0.4-1.0mSv, respectively, and as 5.9-9.0mSv in total.

Nuclear Power Plants Pre-operational Radiological Monitoring Mapping for the Coastal Boarders and Islands of the United Arab Emirates (UAE)

In the light of the peaceful nuclear power plants (NPPs) project of the United Arab Emirates (UAE), the operation license has been issued and the first unit is being in commercial operation. This work deals mainly with radiological surveillance of the coastal boarder and some Islands of UAE as a baseline reference natural and artificial radioactivity mapping. Ultra-sensitive hyper pure Germanium (HpGe) detector was used to carry out the non-destructive gamma measurements. The area of study was divided into; Abu Dhabi region, northern emirates and islands. About 85 soils, shore sediment and water samples were collected based on the scientific sampling mechanism. The samples were analyzed for X-ray diffraction mineralogy (XRD). The radioactivity in Bq/kg of the natural 238U(226Ra), 232Th and 40K were calculated for all the collected samples. The artificial 137Cs was also observed in very low activity. The hazard indices were also calculated and found to be less than the recommended international and regional limits. The correlations between the measured radioisotopes were also depicted. The results were compared, presented and given in 3D histograms.

Optimization of γ-Spectrometry Measurements of Radionuclides of Natural Thorium-232 and Uranium-238 Series

The nuclear-physical properties of radionuclides of natural 232Th and 238U series differ significantly; therefore, the problem of selecting particular γ-lines for calculations arises in direct γ-spectrometry measurements in assessing the absolute activities of the parent radionuclides of these series. In the present study, we develop an approach yielding a reliable value of the specific activity of 232Th and 238U by a single measurement of a sample with the smallest deviation from the true value. We used a bottom sediment sample, taken during the 66th cruise of the Akademik Mstislav Keldysh research vessel in the Kara Sea (station coordinates: 72°30.4' N, 80°20.4' E; depth 14 m), as a model sample. When processing the results, only those lines were selected from the entire set of lines belonging to the 232Th natural series, the quantum yield of which exceeded 2% (taking into account branching). When analyzing the natural 238U series, we selected lines that were free from interference with nuclides of the 232Th series and with the quantum yield above 3%.

Assessment of Natural and Anthropogenic Radioactivity of the Princes’ Islands in the Sea of Marmara

In this study, the activity concentrations of naturally occurring 238U, 232Th and 40K and anthropogenic 137Cs radionuclides were measured for 56 soil and beach sand samples collected from the Princes’ Islands (Istanbul) in the Sea of Marmara, using a gamma-ray spectrometer. In each case, the outdoor gamma-ray dose rates in air were measured at the coordinates where the samples were collected, using a portable gamma-ray detector. In addition, the 210Po specific activity concentrations were measured for 13 different types of fish and 3 black mussel samples that are consumed in the region, using an alpha spectrometer. The mean activity concentrations of natural 238U, 232Th and 40K and artificial 137Cs radionuclides were calculated to be 33.8 ± 0.5 Bq kg−1, 19.3 ± 0.3 Bq kg−1, 429.5 ± 4.5 Bq kg−1 and 8.9 ± 0.1 Bq kg−1, respectively, in the soil and beach sand samples. Activity concentration contour maps of the Princes’ Islands (Istanbul) were constructed. The mean annual effective dose values for natural and artificial radioactive nuclide activity concentrations were determined to be 55.4 μSv y−1 and 1.2 μSv y−1, respectively. The average outdoor gamma-ray dose rate measured in the air was 0.68 mSv y−1. The mean activity concentrations of 210Po in the fish and mussel samples were measured to be 16.2 ± 1.9 Bq kg−1 and 516.1 ± 25.8 Bq kg−1. The average annual effective ingestion doses due to 210Po from the consumption of these seafoods were calculated to be 106.9 μSv y−1 and 619.4 μSv y−1, respectively. The results of this study were compared with the limits proposed by UNSCEAR, ICRP and the values obtained in other similar studies worldwide.

Characterization of Uranium Ore Samples by HPGe Gamma-Ray Spectroscopy

Gamma logging for uranium exploration is currently based on total counting with the Geiger–Muller gas detectors or NaI(Tl) scintillators. However, the total count rate interpretation in terms of uranium concentration may be impaired in case of roll fronts when the radioactive equilibrium of the natural 238U radioactive chain is modified by the differential leaching of uranium and its daughter radioisotopes radium, radon, and so on. Indeed, in the case of secular equilibrium, more than 95% of gamma rays emitted by uranium ores come from 214Pb and 214Bi isotopes that are in the back end of the 238U decay chain. These two isotopes might produce an intense gamma signal even when uranium is not present, or with a much smaller activity, in the ore. Therefore, gamma spectroscopy measurements of core samples are performed on the surface with HPGe detectors to directly characterize uranium activity from the 1001-keV gamma ray of 234mPa that is at the beginning of the 238U chain. However, due to the low intensity of this gamma ray, acquisitions of several hours are needed. In view to characterize uranium concentration within a few minutes, we propose a method using both the 92 keV gamma rays of 234Th and 235U and the 98.4-keV uranium X-ray. This last is due to uranium self-induced fluorescence caused by gamma rays of the uranium chain, mainly 214Pb and 214 Bi. The gamma rays of 214Pb and 214Bi undergo scatterings in the sample leading to photons with energy in the 100-keV range that favor photoelectric interactions and, thus, fluorescence. The comparison of the uranium activity obtained with the 92- and 98.4-keV lines allows detecting a uranium heterogeneity in the ore. Indeed, in the case of uranium nugget, the 92-keV peak leads to underestimated uranium concentration due to the gamma self-absorption, but on the contrary, the 98.4-keV peak leads to an overestimation because of increased fluorescence. In order to test this new approach, tens of uranium ore samples have been measured with a handheld HPGe FALCON 5000 detector.

The use of self-induced X-ray fluorescence in gamma-ray spectroscopy of uranium ore samples

Gamma logging for uranium exploration are currently based on total counting with Geiger Müller gas detectors or NaI (TI) scintillators. However, the total count rate interpretation in terms of uranium concentration may be impaired in case of roll fronts, when the radioactive equilibrium of the natural 238U radioactive chain is modified by differential leaching of uranium and its daughter radioisotopes of thorium, radium, radon, etc. Indeed, in case of secular equilibrium, more than 95 % of gamma rays emitted by uranium ores come from 214Pb and 214Bi isotopes, which are in the back-end of 238U chain. Consequently, these last might produce an intense gamma signal even when uranium is not present, or with a much smaller activity, in the ore. Therefore, gamma spectroscopy measurements of core samples are performed in surface with high-resolution hyper-pure germanium HPGe detectors to directly characterize uranium activity from the 1001 keV gamma ray of 234mPa, which is in the beginning of 238U chain. However, due to the low intensity of this gamma ray, i.e. 0.84 %, acquisitions of several hours are needed. In view to characterize uranium concentration within a few minutes, we propose here a method using both the 92 keV gamma ray of 234Th and the 98.4 keV uranium X-ray. This last is due to uranium self-induced fluorescence caused by gamma radiations of 214Pb and 214Bi, which create a significant Compton scattering continuum acting as a fluorescence source and resulting in the emission of uranium fluorescence X-rays. The comparison of the uranium activity obtained with the 92 keV and 98.4 keV lines allows detecting a uranium heterogeneity in the ore. Indeed, in case of uranium nugget, the 92 keV line leads to underestimated uranium concentration due to gamma self-absorption, but on the contrary the 98.4 keV line leads to an overestimation because of increased fluorescence. In order to test this new approach, several tens of uranium ore samples have been measured with a handheld HPGe FALCON 5000 detector.

A rapid method for quantifying 238Pu in the presence of natural 238U via quadrupole inductively coupled plasma mass spectrometry (ICP-MS) and utilizing a resin-based extraction procedure

A method was developed for removing the interference of 238U from samples containing 238Pu so that the Pu isotopes could be rapidly determined by ICP-MS. The acidified sample was first passed through a commercial TEVA® resin that retained all of the plutonium and some uranium. Second, the sample was further passed through a UTEVA® resin that retained all of the remaining uranium but was free of plutonium. Elution of both of the fractions retained by the two resins and analysis by ICP-MS, allowed a simple correction factor to be determined that enabled subtraction of the interference caused by 238U.

Радиоэкологические аспекты радоновыделения на объектах уранодобывающей промышленности

The main ecological and geochemical feature of uranium extraction industry is a receipt of natural radionuclides (ERN) of
 radioactive families 238U, 235U, 232Th in environment. Radiating pollution is generally caused by natural 238U and products of its disintegration, such as long-living alpha-nuclides 230Th and 226Ra, as well as short-living alpha-nuclides 222Rn (radon) and products of its disintegration. The most dangerous of these products are 210Po, 210Bi and 210Pb. Radon is potentially radioactive carcinogen. Some especially human dangerous radionuclides are formed in the course of its disintegration. The most dangerous of these radionuclides is 210Ро. Polonium poisoning of human body can be predicted in 15—20 years of continuous inhalation of air with radon aerosols. In this regard in areas of uranium ores production and processing it is extremely important to carry out annual calculation of radiating risks under irradiation by radon and affiliated products of its disintegration.

Temporal evolution of radionuclides in sludge from wastewater treatment plants

22 sludge samples were analyzed from three municipal wastewater treatment plants to assess both the occurrence and the temporal behavior of radioactivity during 8 sampling campaigns carried out over the period 2007–2009. As regards natural gamma emitters radionuclides from the natural 238U series (such as 234Th, 214Pb, 214Bi, 210Pb) and the 232Th series (such as 228Ac, 212Pb, 212Bi and 208Tl) and other natural gamma emitters such as 7Be, 210Pbu or 40K were measured. In the case of man-made radionuclides small amounts of 137Cs were found, while significant amounts of 131I were detected in some samples. Correlations were found between radionuclides with the same origin. No seasonal variation for the 238U and 232Th series was found in the studied period but 7Be and 210Pbu showed seasonal variation that was explained by the monthly rainfall. The internal and external hazard indices were calculated and the results indicate that the radiological characteristics of the sludge do not present a significant radiological risk and make them suitable for future applications.

Radioactive elements in natural gas: a case study on distribution of gaseous 222radon and its origin mechanism

As natural gas becomes increasingly important in our daily life, studies have been carried out on trace elements such as mercury and arsenic within it. Other than those, the existence of radioactive gaseous radon from the combustion of natural gas indoors can cause severe diseases and damages to body organs, putting a hazardous impact on human health. At the same time, the radon can also corrode gas production and transportation equipment. A review of the literature on radon concentrations in natural gas produced from gas reservoirs in China and other countries have been studied. Radon is a decay product from 238U, which is closely related to the accumulation and migration of organic matter during diagenesis. Gas recovered from reservoirs with higher than average natural 238U contains higher than average levels of 222Rn. Massive fault systems and fracture zones appear to play a significant role in radon concentrations in natural gas.

The pH-dependence and reversibility of uranium and thorium binding on a modified bauxite refinery residue using isotopic exchange techniques

The pH-dependence and reversibility of uranium and thorium binding onto a modified bauxite refinery residue (MBRR) were studied in laboratory uptake/leaching experiments. Natural 238U and 232Th isotopes were contacted with MBRR in an 8 day loading period (equilibrium pH ≈ 8.5) then leached in pH-dependent experiments, where the pH was decreased from 8 to 3 over several hours following addition of exchange isotopes 232U and 229Th. Relative concentrations of the thorium isotope pair ( 232Th and 229Th) indicate that Th is very strongly bound to MBRR, and although at pH 3, some de-sorption is observed 232Th (≈3%) and 229Th (≈2.5%), released thorium is partially re-adsorbed during an overnight equilibration. During the initial equilibration, approximately 50% of the 238U was adsorbed, and a U adsorption maximum occurs between pH 5 and pH 6, where <0.5% of the U remains in solution. However, at a pH between 5 and 3, some 60% of the bound U releases, hence the pH range of maximum U retention on the MBRR is relatively narrow. When equilibrated overnight, the MBRR releases additional U, suggesting a kinetically controlled de-sorption linked to mineral dissolution. Plots of U isotope exchange between 232U and 238U are linear, and suggest that U adsorption is mostly reversible. Data for adsorption in mixed systems of U and Th suggest that Th and U compete for similar binding sites.

Isotopic composition ( 238U/ 235U) of some commonly used uranium reference materials

We have determined 238U/ 235U ratios for a suite of commonly used natural (CRM 112a, SRM 950a, and HU-1) and synthetic (IRMM 184 and CRM U500) uranium reference materials by thermal ionisation mass-spectrometry (TIMS) using the IRMM 3636 233U– 236U double spike to accurately correct for mass fractionation. Total uncertainty on the 238U/ 235U determinations is estimated to be <0.02% (2σ). These natural 238U/ 235U values are different from the widely used ‘consensus’ value (137.88), with each standard having lower 238U/ 235U values by up to 0.08%. The 238U/ 235U ratio determined for CRM U500 and IRMM 184 are within error of their certified values; however, the total uncertainty for CRM U500 is substantially reduced (from 0.1% to 0.02%). These reference materials are commonly used to assess mass-spectrometer performance and accuracy, calibrate isotope tracers employed in U, U–Th and U–Pb isotopic studies, and as a reference for terrestrial and meteoritic 238U/ 235U variations. These new 238U/ 235U values will thus provide greater accuracy and reduced uncertainty for a wide variety of isotopic determinations.

Production cross section of 236Th in the interaction of 238U with 60 MeV/u 18O ions

The neutron-rich target-like isotope 236Th has been produced in the 238U-2p multinucleon transfer reaction between a 60 MeV/u 18O beam and natural 238U targets. The activities of thorium were determined after radiochemical separation of Th from the mixture of uranium and reaction products. The 236Th isotope was identified by the characteristic γ-rays of 642.2, 687.6 and 229.6 keV. The production cross section of 236Th was determined to be 250±50 μb.

An examination of uranium levels in Canadian forces personnel who served in the Gulf War and Kosovo.

A uranium bioassay program was conducted involving 103 active and retired Canadian Forces personnel. The total uranium concentrations in each of two 24-h urine collections were analyzed separately at independent commercial laboratories by inductively coupled plasma mass spectrometry (ICP-MS) and by instrumental neutron activation analysis (INAA). The mean and median concentrations were determined to be 4.5 ng L(-1) and 2.8 ng L(-1), respectively, from ICP-MS and 17 ng L(-1) and 15 ng L(-1), respectively, from INAA. The total uranium concentrations were sufficiently low so that isotopic (238U:235U ratio) assays could not be performed directly from urine samples. Isotopic assays were performed on hair samples from 19 of the veterans participating in the testing. The isotopic hair assays were scattered around the natural 238U:235U ratio of 137.8, ranging from 122 +/- 21 to 145 +/- 16 (1sigma). Due to concern expressed in the media over possible depleted uranium exposure and long-term retention in bone, a single bone sample (vertebrate bone marrow) from a deceased member of the Canadian Forces was also analyzed for total uranium content and isotopic ratio by ICP-MS. The sample was shown to have 16.0 +/- 0.3 microg kg(-1) uranium by dry weight and a 238U:238U isotopic ratio of 138 +/- 4, consistent with natural uranium.

A Multisystem Modeling Approach for Uranium-Series Dating

The sensitivity of the dating of long-term uranium attachment to bedrock fractures was studied using radioactive dis-equilibria in the natural 238U decay chain. For this purpose, fracture coating samples were taken from the uranium deposit at Palmottu, Finland. A general simulation model was derived for the evolution of the 234U/238U and 230Th/234U disequilibria. Instantaneous, continuous, and multistage uranium accumulation modes were tested to see their effect on the model age. All accumulations produced different, but internally consistent, model ages, except the multistage scenario that yielded a nonunique dating. The simulation model and scenario technique provide a good modeling approach, and the real challenge in uranium-series dating appears to be the quantification of the accumulation rates.

The natural radioactivity in phosphate deposits from Sudan

The natural radionuclide content of phosphate deposits at Uro and Kurun in Eastern Nuba mountains in the state of Kordofan (Western Sudan) and soils was determined radiochemically and gamma spectrometrically. The analyses were performed for natural uranium and thorium, 210Po, 226Ra and 40K. The data indicate that 238U and its decay products contribute primarily to the high natural radioactivity of phosphate ores. At maximum, we found an activity concentration of 2600 Bq/kg natural 238U. From the values obtained, the dose rates over agricultural areas, resulting from the use of ground rock phosphate as fertilizers estimated under extremely conservative assumptions, result in an additional external radiation exposure for members of the population of 5.42 × 10−9 nGy/a and 1.13 × 10−9 nGy/a for Uro and Kurun rock phosphates, respectively. These results show that the natural radionuclides contained in Uro and Kurun ground rock phosphate contribute very little to the average terrestrial radiation exposure to the population.

Effect of sediment type, temperature and colloids on the transfer of radionuclides from water to sediment

The effect of natural organic (O), sand (S) and clay (C) sediments, temperature (5, 15 and 25°C) and colloids on the transfer of 60Co, 65Zn, 134Cs and natural 238U from freshwater to sediments was investigated in the laboratory using lake sediment/water columns. Sediment type had a significant effect on the loss of these radionuclides from water. Loss of 60Co, 65Zn and 238U from water was generally in the order O > C > S sediment. Loss of 134Cs from water was in the order C > O > S sediment. Generally the loss of the radionuclides from water was greater at higher temperatures and was in the order 60Co > 65Zn > 134Cs > 238U. The presence of colloids slowed the loss of the radionuclides from water. Transfer rates of 0·014–0·077 d −1 for 60Co, 0·010–0·0.110 d −1 for 65Zn, 0·015–0·092 d −1 for 134Cs and 0·001–0·084 d −1 for 238U were measured depending on expirimental conditions and were in general agreement with the range of values reported from field studies.

Cyclotron production of gamma-emitting actinides as tracers for metabolic and waste disposal studies

Cyclotron production of gamma-emitting actinides as tracers for metabolic and waste disposal studies