Uranium-series disequilibria as a means to study recent migration of uranium in a sandstone-hosted uranium deposit, NW China.

Uranium concentration and alpha specific activities of uranium decay series nuclides (234)U, (238)U, (230)Th, (232)Th and (226)Ra were measured for 16 oxidized host sandstone samples, 36 oxic-anoxic (mineralized) sandstone samples and three unaltered primary sandstone samples collected from the Shihongtan deposit. The results show that most of the ores and host sandstones have close to secular equilibrium alpha activity ratios for (234)U/(238)U, (230)Th/(238)U, (230)Th/(234)U and (226)Ra/(230)Th, indicating that intensive groundwater-rock/ore interaction and uranium migration have not taken place in the deposit during the last 1.0 Ma. However, some of the old uranium ore bodies have locally undergone leaching in the oxidizing environment during the past 300 ka to 1.0 Ma or to the present, and a number of new U ore bodies have grown in the oxic-anoxic transition (mineralized) subzone during the past 1.0 Ma. Locally, uranium leaching has taken place during the past 300 ka to 1.0 Ma, and perhaps is still going on now in some sandstones of the oxidizing subzone. However, uranium accumulation has locally occurred in some sandstones of the oxidizing environment during the past 1 ka to 1.0 Ma, which may be attributed to adsorption of U(VI) by clays contained in oxidized sandstones. A recent accumulation of uranium has locally taken place within the unaltered sandstones of the primary subzone close to the oxic-anoxic transition environment during the past 300 ka to 1.0 Ma. Results from the present study also indicate that uranium-series disequilibrium is an important tool to trace recent migration of uranium occurring in sandstone-hosted U deposits during the past 1.0 Ma and to distinguish the oxidation-reduction boundary.     

The natural radioactivity in Guarani aquifer groundwater, Brazil.

The measurements of gross alpha and gross beta radioactivity in groundwater samples from Guarani aquifer in Brazil are reported in this paper together with the activity concentration of the natural dissolved radionuclides (40)K, (238)U, (234)U, (226)Ra, (222)Rn, (210)Po, (210)Pb, (232)Th, (228Th), and (228)Ra. Most of the gross alpha radioactivity values were below the critical level of detection corresponding to 1mBq/L, however, the whole data set for the gross beta radioactivity and radionuclides (40)K, (238)U, (234)U, (226)Ra, (222)Rn, (210)Po, (210)Pb, and (228)Ra was submitted to a statistical treatment, considering class intervals arranged in geometric progression, because of the great variability of the activity. The analysis indicated lognormal distribution of the data, as usually observed in samples taken from the natural context. An inverse relationship between the gross alpha and gross beta activity has been identified and is related to an increase in the K content in the water. The mobility coefficient has been estimated for (238)U, (226)Ra, (232)Th and (228)Ra in Guarani aquifer and the results indicated that the radioelement solubility in the studied system varies according to the following order: radium>uranium>thorium. The implications of the data obtained in terms of standards established for defining the drinking water quality have also been discussed.     

Spatial and monthly variations of radium isotopes in produced water during oil production.

Spatial and monthly variations of radium isotope concentrations in produced water have been evaluated during oil production. Samples of produced water were collected and analyzed on a monthly basis over a period of 5 months, the samples being derived from 11 main oil production wells at three Syrian oilfields. The highest average 226Ra, 228Ra and 224Ra concentrations in these samples of water were found to be 41, 37.5 and 1.1 Bql(-1), respectively. The data obtained for 226Ra, 228Ra and the 228Ra/226Ra activity ratio were evaluated statistically and displayed using the Box Plot method; clear variations can be observed from one field to another, indicating differences in the geological formation of the reservoir. The 228Ra/226Ra activity ratio variations reflect the variability of the Th/U mass ratio of the geological formation, suggesting two different source rock types. The calculated mean Th/U mass ratio for these two possible types of source rock were 2.4 and 5.78. In addition, the 228Ra/226Ra mean activity ratio was also used to estimate the age of some deposited scales in tubulars; the results were compared with the 224Ra/228Ra activity ratio dating method. Monthly variations of 226Ra and 228Ra activity concentrations and the 228Ra/226Ra activity ratio in produced water were also observed, the major causes for these variations being related to the type of injection water and interwell reactions. Possible relationships between 226Ra and 228Ra activity concentrations, the 228Ra/226Ra activity ratio and physical and chemical properties of produced water were statistically evaluated; no linear correlations were found.     

Natural radioactivity in underground water from the Outer Carpathians in Poland with the use of nuclear spectrometry techniques

The investigations of natural radioactivity in underground mineral water and spring water in health resorts in the Outer Carpathians were performed. Samples from 40 water springs were collected 3–4 times over a period of 10 years (1997–2007). In order to obtain necessary data, two different nuclear spectrometry techniques were applied: WinSpectral α?β 1414 liquid scintillation counter from Wallac and α-spectrometer 7401 VR from Canberra–Packard, USA with the silicon surface barrier detector. The activity concentrations of ²²²Rn in the investigated samples varied from below 1 to 50 Bq/l. For radium isotopes the concentrations were in a range from below 10 to 490 mBq/l for ²²⁶Ra and from 29 to 397 mBq/l for ²²⁸Ra. The highest concentrations for both radium isotopes were obtained for medicinal water Zuber III from Krynica spa. The activity concentrations for uranium isotopes varied from below 0.5 to 16 mBq/l for ²³⁸U and from below 0.5 to 162 mBq/l for ²³⁴U with the highest values obtained for water Zuber IV. The highest annual effective dose arising from mainly radium isotopes was obtained for Zuber III water and was equal to 75 μSv/yr. Additionally, the annual effective doses due to ²²²Rn consumed with water were also estimated. The isotopic ratios between isotopes originating from the same decay chain (²³⁴U/²³⁸U, ²²⁶Ra/²³⁸U) and from different radioactive decay chains (²²⁶Ra/²²⁸Ra) were determined. The correlations between different isotopes were presented.     

Behavior and environmental impacts of radionuclides during the hydrometallurgy of calcareous and argillaceous rocks, southwestern Sinai, Egypt

The hydrometallurgy of radionuclides means getting the radioelements from the rocks into solution by leaching, getting the radionuclides from the solution by extraction process, and then precipitation of the desired elements to obtain concentrate. The follow-up of the radionuclides during these processes is the main target of this work to identify the identity of the original samples, pregnant solutions (leachates), residuals and the concentrate. Six samples were chosen to achieve this work. The leaching process was carried out under the conditions; 20-30% acid (H(2)SO(4)) concentration, 1:3 solid/liquid ratios, 60 min stirring time at room temperature. The activity concentrations of (238)U, (235)U, (234)U, (226)Ra, (214)Pb, (214)Bi, (232)Th and (40)K were measured in the original samples, residuals and U-concentrate (Bq/kg), and leachates (Bq/?). The results indicate that, the radionuclides before (226)Ra in the (238)U decay series are more leachable (released) than those from (226)Ra to (214)Bi in the order; (234)U>(238)U=(235)U > (226)Ra>(214)Pb>(214)Bi. (232)Th and (40)K are immobile under the present conditions. The radiological hazards of natural radioactivity in the original samples, leachates, residuals and U-concentrate were calculated and compared with the internationally recommended values and were found to be much higher than the world average values.     

Certified reference material for radionuclides in fish flesh sample IAEA-414 (mixed fish from the Irish Sea and North Sea).

A certified reference material (CRM) for radionuclides in fish sample IAEA-414 (mixed fish from the Irish Sea and North Seas) is described and the results of the certification process are presented. Nine radionuclides (40K, 137Cs, 232Th, 234U, 235U, 238U, 238Pu, 239+240Pu and 241Am) were certified for this material. Information on massic activities with 95% confidence intervals is given for six other radionuclides (90Sr, 210Pb(210Po), 226Ra, 239Pu, 240Pu 241Pu). Less frequently reported radionuclides (99Tc, 129I, 228Th, 230Th and 237Np) and information on some activity and mass ratios are also included. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in fish sample, for the development and validation of analytical methods and for training purposes. The material is available from IAEA, Vienna, in 100 g units.     

Uranium and thorium series disequilibrium in quaternary carbonate deposits from the Serra da Bodoquena and Pantanal do Miranda, Mato Grosso do Sul State, central Brazil.

Activities of gamma-ray emitting members of the uranium (238U) and thorium (232Th) series were measured in a quaternary limestone deposit that outcrops in the southeastern Pantanal Matogrossense Basin and in quaternary tufas deposited at the drainage of the Serra da Bodoquena. It is a first step in a study of the mobilization of uranium and thorium series and its relation to surface hydrology, in a region where carbonate deposits are being continuously dissolved and reprecipitated. The obtained results show that all these deposits are characterized by very low concentrations of uranium and thorium. The 238U/226Ra and 228Th/228Ra activity ratios are significantly different than 1.0, indicating that both series are in radioactive disequilibrium. Although the Serra da Bodoquena deposits seem to be very recent, their very fine granulation and high porosity suggest that they behave as open systems for geochemical exchanges of uranium and thorium series members. The Pantanal do Miranda limestone has a radiocarbon age of 3900 yr BP. Since the thorium series is in disequilibrium it is also concluded that this deposit behaves as an open system for geochemical exchanges.     

238U 226Ra 210Pb, 232Th and 40K activities in soil profiles of the Flysch sector (Central Spanish Pyrenees).

Distributions of natural gamma-emitting radionuclides were determined in three soil profiles developed on Tertiary sedimentary materials in mountain landscapes of the Central Spanish Pyrenees. Radioisotope activities (Bq kg(-1)) lie in the range of 0-53 for 238U; 19-33 for 226Ra; 7-75 for 210Pb; 24-48 for 232Th and 335-562 for 40K. 238U and 210Pb activities show an important variability down the soil profiles. 238U was markedly depleted in all upper soil layers and highly enriched in lower layers of two soil profiles. 210Pb exhibits very dissimilar distribution patterns in all three soils. 226Ra and 232Th had quite uniform depth distributions. 40K showed depletion in both upper and lower layers in one soil profile but remained fairly constant in the other two profiles. 238U/226Ra activity ratios (ARs) have been used to assess equilibrium in the 238U decay chain and as indicators of edaphogenesis in the studied soil profiles. Maintenance of initial proportionality in the ratio of 232Th/238U activities has been assessed through ARs of their progenies. Additionally, a variety of soil properties were measured down the soil profiles. Among soils, variation in radionuclide activies may be due to differences in carbonate content, organic matter and/or grain size. In this environment, soil properties differently affect mobilization of natural radionuclides. The association of some radiologic properties with soil layers suggest a relationship between soil processes and radionuclide distribution.     

Study of natural radioactivity and the state of radioactive disequilibrium in U-series for rock samples, North Eastern Desert, Egypt.

Twenty rock samples collected from North Eastern Desert in Egypt have been investigated. Natural radionuclide contents have been measured by gamma-ray spectrometry employing a shielded HPGe detector. The activities of (238)U, (232)Th and (40)K have been determined in Bq/kg dry weight. The absorbed dose rate of gamma radiation ranged from 100.48 to 22,140.53 nGy/h. The representative external hazard index values (H(ex)) for the corresponding samples were estimated. In the present work, the state of radioactive disequilibrium in the U-series at Wadi Baligh area was studied. The activity ratios between (226)Ra/(214)Pb and (214)Pb/(214)Bi were measured. The thorium-to-uranium concentration ratios (Clark value) were also estimated.     

Distribution of scales containing NORM in different oilfields equipment.

Evaluation has been made of the distribution of hard scales containing naturally occurring radioactive materials (NORM) in a range of oilfield equipment in Syrian oilfields. One hundred and fifty-two scale samples from oilfield equipment were collected and analysed for radioactivity, elemental and mineralogical compositions. The average 226Ra, 228Ra and 224Ra concentrations in scales were found to be 174, 91 and 67 Bqg(-1), respectively; the highest value of 226Ra was found to be 1520 Bqg(-1). A gradual increase in 226Ra specific activity from down-hole tubulars to surface parts of the installations was observed. The 228Ra/226Ra mean activity ratio was observed to be 0.76, indicating a Th/U mass ratio of about 2.3. This value can be considered a fingerprint for the Th/U mass ratio of the geological formation of the reservoir. Radium isotopic data were also used to estimate the age of the deposited scales using the 224Ra/228Ra activity ratio; the highest average age (5.3 years) was found to be in scales collected from valves. Multiple regressions of the data have shown that 226Ra is more highly correlated with Ba and Sr content in scales (R2=0.92) than Ca. Around 77% of 226Ra was found to be incorporated with anhydrate barium strontium sulphate (R2=0.93), solubility in water being very low to negligible; lower levels of radium isotopes were found in calcite.     

Transfer of 238U, 230Th, 226Ra,and 210Pb from soils to tree and shrub species in a Mediterranean area

The soil-to-plant transfer factors of natural uranium isotopes (²³⁸U and ²³⁴U), ²³⁰Th, ²²⁶Ra, and ²¹⁰Pb were studied in a disused uranium mine located in the Extremadura region in the south-west of Spain. The plant samples included trees (Quercus ilex, Quercus suber, and Eucalyptus cameldulensis) and one shrub (Cytisus multiflorus). All of them are characteristic of Mediterranean environments. The activity concentrations in leaves and fruit were determined for the tree species at different stages of growth. For the shrub, the total above-ground fraction was considered in three seasons. For old leaves and fruit, the highest activity concentrations were found in Eucalyptus cameldulensis for all the radionuclides studied, except in the case of ²³⁰Th that presented similar activity concentrations in all of the tree species studied. In every case, the transfer to fruit was less than the transfer to leaves. In the shrub, the results depended on the season of sampling, with the highest value obtained in spring and the lowest in autumn. Important correlations were obtained for ²³⁸U and ²²⁶Ra between the activity ratio in soils with that in leaves or fruit.     

Radioactivity levels of recent sediments in the Butrint Lagoon and the adjacent coast of Albania.

Sediment samples have been collected in the Butrint area, located in the south-west Albania to determine the radioactivity levels of (40)K, (137)Cs, (212)Bi, (212)Pb, (214)Bi, (214)Pb, (226)Ra and (228)Ac on the bed of the lagoon and adjacent sea, using direct counting gamma spectroscopy. The concentration of (137)Cs and (40)K varied from 2.8 to 37.5 Bq/kg and from 266 to 675 Bq/kg dry weight (dw), respectively (central values). The average concentrations of (238)U and (232)Th daughter products varied from 8 to 27 Bq/kg and from 13 to 40 Bq/kg dw, respectively. The measured (235)U activity ranged from 0.7 to 2.5 Bq/kg dw. Samples of different sedimentary properties, studied for the radioactivity concentration, revealed an inversely proportional relation between grain size and a linear combination of measured specific activities of (226)Ra, (232)Th ((228)Ac, (212)Bi and (212)Pb), (40)K and (137)Cs.     

EC comparison on the determination of 226Ra, 228Ra, 234U and 238U in water among European monitoring laboratories

In anticipation of new European requirements for monitoring radioactivity concentration in drinking water, IRMM organized an interlaboratory comparison on the determination of low levels of activity concentrations (about 10–100 mBq L^?1) of the naturally occurring radionuclides ²²⁶Ra, ²²⁸Ra, ²³⁴U and ²³⁸U in three commercially available mineral waters. Using two or three different methods with traceability to the International System of Reference (SIR), the reference values of the water samples were determined prior to the proficiency test within combined standard uncertainties of the order of 3%–10%. An overview of radiochemical separation and measurement methods used by the 45 participating laboratories are given. The results of the participants are evaluated versus the reference values. Several of the participants’ results deviate by more than a factor of two from the reference values, in particular for the radium isotopes. Such erroneous analysis results may lead to a crucial omission of remedial actions on drinking water supplies or to economic loss by an unjustified action.     

The effect of uranium migration on radionuclide distributions for soil samples at the El-Gor area,Sinai, Egypt

The concentrations and distributions of the activity of natural radionuclides in soil samples were investigated in fifteen soil samples at El-Gor area representing two profiles (A and B) using a HP–Ge detector and alpha counting by SSNTD (CR-39), respectively. The average concentrations of the radionuclides ²³⁸U, ²²⁶Ra, ²³⁵U, ²³²Th and ⁴⁰K are 203.4, 177.23, 9.77, 43.33 and 386.22 Bq kg⁻¹ (dry weight), respectively, and profile A and ²³⁸U, ²²⁶Ra, ²³⁵U, ²³²Th and ⁴⁰K have average concentrations of 232.58, 246, 11.7, 31.7, and 277.07 Bq kg⁻¹ for profile B, respectively. The eTh and eU were estimated to detect the migration process of uranium into or out of an area or uranium to or from the studied profiles. The results indicate a migration of uranium by 29% for profile A and 65.37% for profile B. The activity ratio (²³⁸U/²²⁶Ra) was found to be 0.9 in profile A and 1.15 in profile B. These ratios coincide with the uranium migration processes. The responsible mass corresponding to the measured ²²⁶Ra activity was also calculated. The radon activity concentrations for the two profiles are nearly 300 Bq m⁻³. The emanation coefficient (η) was calculated from the ratio of the expected radon activity to the measured radon for the studied soil samples. The value of η was found to depend only on the radium activity regardless to soil formation.     

Radium content in ground water from a granitic batholith of the metamorphic basement,eastern São Paulo State,Brazil

The radon emanation method was applied to measure the activity of ²²⁶Ra, dissolved and associated with suspended solids, in the ground waters from two wells drilled in the Morungaba Batholith fractured granites, intruded in the metamorphic basement, eastern border of the Paraná basin in São Paulo State, Brazil. The water samples were collected from March 2003,to April 2004, with a time interval of about one month between sampling campaigns. The mean observed dissolved ²²⁶Ra activity concentrations in the two wells were 47.9±7.1 and 51.6±8.8 mBq/L. No systematic time dependence of the ²²⁶Ra activity concentration was clearly identified. The activity of ²²⁶Ra associated with suspended solids contained in 1 L of ground water fell, during the sampling period, from 13±1 to 0.8±0.1 mBq in one well and from 4.9±0.3 to 0.6±0.1 mBq in the second well.     

Investigation of natural radioactivity levels in water around Kadugli, Sudan.

Surface water from Miri Lake and groundwater from around Kadugli (West-Central Sudan) obtained by means of hand-pumps was analysed for (238)U, (226)Ra, (222)Rn, and (232)Th activity concentrations. The surface water showed very low levels of radionuclide concentrations: <1.0-7.5, 8.5-16.5, <1.6, and <0.1-0.39mBqL(-1) for (238)U, (226)Ra, (222)Rn, and (232)Th, respectively. Groundwater revealed a significant amount of natural radioactivity (16.1-1720, 7.7-14.3, 3000-139,000, <0.1-39mBqL(-1)) respectively. The overall annual effective dose was below the WHO reference dose level of 0.1mSvyr(-1) except in one groundwater sample with an associated dose of 0.7mSvyr(-1).     

Estimation of radiation doses to members of the public in Italy from intakes of some important naturally occurring radionuclides (238U, 234U, 235U, 226Ra, 228Ra, 224Ra and (210)Po) in drinking water.

The radiological quality in some samples of drinking water collected in Italy has been evaluated in the paper. As far as the measured alpha or beta radionuclides are concerned, the doses for all the analysed samples of drinking water are in the range of 1.80-36.2microSvyr(-1), all being well below the reference level of the committed effective dose (100microSvyr(-1)) recommended by the WHO. As far as each measured alpha or beta radionuclide is concerned, the dose contributions for most of the analysed water samples are in this order: 210Po228Ra>226Ra>234U238U>224Ra>235U, and (210)Po and (228)Ra can yield a significant contribution to the doses from the analysed drinking water samples. As far as the elements are concerned, the dose contributions are 48.0+/-27.9% from radium, 31.7+/-23.1% from polonium, and 20.3+/-14.1% from uranium. The water samples, No. 2, 7, 13, and 15, can lead to a dose of >10microSvyr(-1), mainly due to the dose contribution from (210)Po and 228Ra, especially water samples No. 2 and 13. The obtained data can provide basic information for consumers and competent authorities regarding the internal exposure risk due to drinking water intake, and can possibly serve as a comparison when evaluating the dose contribution from artificial radionuclides released to the environment as a result of any human practices and accidents in the studied area.     

Simultaneous determination of 226Ra, 233U and 237Np by liquid scintillation spectrometry.

A method has been developed for the simultaneous determination of 226Ra, 233U and 237Np by liquid-scintillation (LS) spectrometry. This method consists of the evaluation of the alpha-spectrum that is composed of the strongly overlapping peaks of 226Ra, 233U, 237Np, 222Rn and 218Po in the energy range of 4.60-6.00 MeV and the single 214Po peak at 7.69 MeV. The alpha-peaks are analysed by a special peak fit function that considers the deviation of the alpha-peak at the low energy side from the pure Gaussian shape. First 237Np is determined using its daughter 233Pa by analysing the beta-spectrum in the range 150-570 keV. 226Ra follows from the alpha-spectrum that is measured 6 weeks after sample preparation, i.e., 226Ra is determined from the radioactive equilibrium with its short-lived daughters 222Rn, 218Po and 214Po. Finally the 233U activity results from the fitted spectrum in the range of 4.4-4.8 MeV by subtracting the activity of 226Ra and 237Np. Knowing the exact energy position of the LS-peaks an alternative evaluation consists in the accurate deconvolution of the first three peaks that are formed by 226Ra and 233U (maximum of both at channel 700), 237Np (maxima at channels 700 and 725) and 222Rn (maximum at channel 737). In these two ways 226Ra, 233U and 237Np can be determined in mutual activity ratios of 1:50 with a relative standard deviation of less than 4% for the major activity and 9% for the minor activity.     

Determination of the natural radioactivity levels in north west of Dukhan, Qatar using high-resolution gamma-ray spectrometry

This study is aimed at the determination of the activity concentrations of naturally occuring and technologically enhanced levels of radiation in 34 representative soil samples that have been collected from an inshore oil field area which was found to have, in a previous study, the highest observed value of 226Ra concentration among 129 soil samples. The activity concentrations of 238U and 226Ra have been inferred from gamma-ray transitions associated with their decay progenies and measured using a hyper-pure germanium detector. Details of the sample preparation and the gamma-ray spectroscopic analysis techniques are presented, together with the values of the activity concentrations associated with the naturally occuring radionuclide chains for all the samples collected from NW Dukhan. Discrete-line, gamma-ray energy transitions from spectral lines ranging in energy from ～100 keV up to 2.6 MeV have been associated with characteristic decays of the various decay products within the 235.8U and 232Th radioactive decay chains. These data have been analyzed, under the assumption of secular equilibrium for the U and Th decay chains. Details of the sample preparation and the gamma-ray spectroscopic analysis techniques are presented. The weighted mean value of the activity concentrations of 226Ra in one of the samples was found to be around a factor of 2 higher than the values obtained in the previous study and approximately a factor of 10 higher than the accepted worldwide average value of 35 Bq/kg. The weighted mean values of the activity concentrations of 232Th and 40K were also deduced and found to be within the worldwide average values of 30 and 400 Bq/kg, respectively. Our previous study reported a value of 201.9±1.5Stat.±13Syst.Bq/kg for 226Ra in one sample and further investigation in the current work determined a measured value for 226Ra of 342.00±1.9Stat.±25Syst.Bq/kg in a sample taken from the same locality. This is significantly higher than all the other investigated soil samples in the current and previous works. Notably, the Th levels in the same sample are within the worldwide average expectations, implying that the increased 226Ra concentration arises from TENORM processes.     

Determination of radioactivity levels and hazards of soil and sediment samples in Firtina Valley (Rize, Turkey).

The natural radioactivity levels in soil and sediment samples of Firtina Valley have been determined. To our knowledge, there seems to be no information about radioactivity level in the Firtina Valley soils and sediments so far. For this reason, soil and sediment samples were collected along the Firtina Valley and analysis on the collected samples were carried out to determine 238U, 232Th, 40K and 137Cs radioisotopes using high purity germanium detector. The activity concentrations obtained for 226Ra, 214Pb, 214Bi, 228Ac, 208Tl, 40K and 137Cs are given in the unit of Bq/kg. The results have been compared with other radioactivity measurements in different country's soils and sediments. The radium equivalent activity (Raeq), the absorbed dose rate (D), the external hazard index (Hex), the annual gonadal dose equivalent (AGDE) and the annual effective dose equivalent (AEDE) were also calculated and compared with the international recommended values.