Determination of the four natural Ra isotopes in thermal waters by gamma-ray spectrometry

Our method for the simultaneous determination of the four natural Ra isotopes (²²⁶Ra, ²²⁸Ra, ²²⁴Ra and ²²³Ra) in thermal waters involves a separation of Ra on a selective filter (3 M EMPORE? Radium Rad disk), and a single counting using a broad-energy HPGe detector (BE Ge manufactured by CANBERRA?). The calculation of ²²³Ra and ²²⁸Ra activities requires interference and cascade summing corrections. The ²²⁶Ra activities in CO₂-rich thermal waters of the Lodève Basin (South of France) range from 530 to 2240 mBq/l. The low (²²⁸Ra/²²⁶Ra) activity ratios (0.19–0.29) suggest that Ra is mostly derived from the aquifer carbonates. The short-lived ²²⁴Ra and ²²³Ra are probably added to the water through recoil or desorption processes from Th-enriched coatings on the fracture walls.     

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.     

222Rn, 226Ra and hydrochemistry in the Bauru Aquifer System,São José do Rio Preto (SP), Brazil

In this paper, the ²²²Rn and ²²⁶Ra activity concentration was measured in groundwater samples collected from the Bauru Aquifer System, São José do Rio Preto city, São Paulo State, Brazil. The site has been selected for a detailed radiometric survey due to the large number of tubular wells drilled in the aquifer there, which provide water for ~70% of the local population. Despite the importance of groundwater for the local water-supply system, there is a lack of both ²²²Rn and ²²⁶Ra data in the municipality. Establishment of these data is relevant to assure that the water quality from a radiological point of view, is not health threat. São José do Rio Preto city is geologically situated in Bauru Group that is located within the Paraná sedimentary basin. The monitoring program involved the collection of 50 groundwater samples from deep tubular wells during three field campaigns held from 17th to 19th January 2011, from 2nd to 3rd August 2011 and in 30th November 2011. Temperature and pH readings were realized in the field, whereas ²²²Rn and ²²⁶Ra analysis were performed at the laboratory using the Alpha Guard-Aquakit analytical protocol, which allowed us to obtain ²²²Rn activity concentration ranging from 0.69 to 14.95 Bq/L. These data indicate that the abundances of ²²²Rn and ²²⁶Ra in the groundwater system of Bauru Group is below the WHO guideline limit of 100 Bq/L. Chemical analysis has been also realized for major cations and anions in order to better understand the water features in the municipality.     

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.     

Relationship between radioactivity of radium and concentrations of barium and lead in hokutolite

Hokutolite consists of barite (BaSO₄) and anglesite (PbSO₄), and contains significant amounts of radium isotopes as a radioactive mineral. Photon activation and gamma-ray spectrometry were employed to determine Ba, Pb and ²²⁶Ra contents in hokutolite samples and to investigate the correlation between ²²⁶Ra activity and both Ba and Pb content. ²²⁶Ra activity in 30 hokutolite samples were estimated in the range of 40–65 Bq/g and was positively related to Ba content (r=0.859, p<0.001), but independent of Pb content (r=−0.236, p=0.217). Experimental results implied that ²²⁶Ra preferably precipitated with Ba over Pb. The ²²⁶Ra activity in hokutolite from the Peitou Hot Spring was experimentally estimated based on the Ba/Pb ratio and expressed as ²²⁶Ra (Bq/g)=14.67 (Ba/Pb)_molar+14.13.     

Radium-226 concentration in spring water sampled in high radon regions

Water ²²⁶Ra concentration in springs was measured in regions with high indoor radon: Ural, North Caucasus (Russia), Niska Banja (Serbia), Piestany (Slovakia), and Issyk-Kul (Kyrgyzstan). This paper presents the results for ²²⁶Ra concentration above 0.03 Bq l^–1. Radium in water could indicate indoor radon problem in the region and water investigation is useful at the initial stage of radon survey. Even low ²²⁶Ra concentration in water (0.1–0.6 Bq l^–1) caused high ²²⁶Ra activity in travertine (up to 1500 Bq kg^?1), which resulted in indoor radon concentration above 2000 Bq m^?3 (Niska Banja).     

Radon in groundwater and dose estimation for inhabitants in Spas of the Sudety Mountain area,Poland

Studies of radon isotope ²²²Rn activity concentration in underground water in the Sudety region were performed with the use of the liquid scintillation technique. Waters chosen for investigations were collected in 24 health resorts and towns of the Sudety area from 115 springs, wells and intakes. The ²²²Rn activity concentration varied within the range from 4.2±0.4 to 1703±55 Bq/l. The annual effective doses due to the consumption of ²²²Rn with water were calculated for 50 sources of underground spring water or tap water used for consumption. The results were within the range from 0.003 to 1.1 mSv/yr, assuming 0.5 l of tap water per day from which radon is not removed or 0.5 l of mineral spring water consumed daily. The contribution to the effective dose from the inhalation of radon during the daily usage of domestic water substantially increases its effective dose.     

Distribution of naturally occurring radionuclides activity concentration in East Malaysian marine sediment

Studies of naturally occurring radioactive materials (NORM) distribution of ²²⁶Ra, ²²⁸Ra and ⁴⁰K in East Malaysia were carried out as part of a marine coastal environment project. The results of measurements will serve as baseline data and background reference level for Malaysia coastlines. Sediments from 21 coastal locations and 10 near shore locations were collected for analyses. The samples were dried, finely ground, sealed in a container and stored for a minimum of 30 days to establish secular equilibrium between ²²⁶Ra and ²²⁸Ra and their respective radioactive progenies. They were counted using a high-purity germanium (HPGe) spectrometer covering the respective progeny energy peak. For ⁴⁰K, the presence of this was measured directly via its 1460 keV energy peak. The concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K in samples obtained from coastal Sarawak ranged between 23 and 41 (mean 30±2) Bq/kg, 27 and 45 (mean 39±4) Bq/kg and 142 and 680 (mean 462±59) Bq/kg, respectively. Meanwhile, the concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K for samples obtained from coastal Sabah ranged between 16 and 30 (mean 23±2) Bq/kg, 23 and 45 (mean 35±4) Bq/kg and 402 and 842 (mean 577±75) Bq/kg, respectively. For the Sarawak near shore stations, the concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K ranged between 11 and 36 (mean 22±2) Bq/kg, 21 and 65 (mean 39±5) Bq/kg and 149 and 517 (mean 309±41) Bq/kg, respectively. Meanwhile, the concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K for samples obtained from Sabah ranged between 9 and 31 (mean 14±2) Bq/kg, 10 and 48 (mean 21±3) Bq/kg and 140 and 580 (mean 269±36) Bq/kg, respectively. The calculated external hazard values of between 0.17 and 0.33 (less than unity) showed that there is little risk of external hazard to the workers handling the sediments.     

Assessment of natural radioactivity levels and radiation hazards due to cement industry

The cement industry is considered as one of the basic industries that plays an important role in the national economy of developing countries. Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in Assiut cement and other local cement types from different Egyptian factories has been measured by using γ-ray spectrometry. From the measured γ-ray spectra, specific activities were determined. The measured activity concentrations for these natural radionuclides were compared with the reported data for other countries. The average values obtained for ²²⁶Ra, ²³²Th and ⁴⁰K activity concentration in different types of cement are lower than the corresponding global values reported in UNSCEAR publications. The obtained results show that the averages of radiation hazard parameters for Assiut cement factory are lower than the acceptable level of 370 Bq kg^?1 for radium equivalent Ra_eq, 1 for level index Iγr, the external hazard index Hex ≤1 and 59 (nGy h^?1) for absorbed dose rate. The manufacturing operation reduces the radiation hazard parameters. Cement does not pose a significant radiological hazard when used for construction of buildings.     

A new low-level γ-ray spectrometry system for environmental radioactivity at the underground laboratory Felsenkeller

A low-level γ-ray spectrometry system, based on an HPGe-detector with 92% relative efficiency recently installed in the underground laboratory Felsenkeller at 110 m water equivalent (w.e.) depth, is described. The integral background count rate normalised to the Ge-crystal mass in the energy range from 40 keV until 2.7 MeV of 0.034 s⁻¹ kg⁻¹ has been achieved by careful material selection of the detector construction material, a graded shielding construction and effective radon suppression. The detector is highly suitable for the effective surveillance of water for human consumption with decision thresholds for ²²⁶Ra and ²²⁸Ra in the order of some mBq L⁻¹.     

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.     

Variation of radon exposure in Damascus dwellings

In the present work, activity concentrations of ²²²Rn in air and ²²²Rn and ²²⁶Ra in drinking water were measured in Damascus city covering its old and modern parts.It was found that the average air radon activity concentration in the old part was higher than in the modern part, and in drinking water, radon was found to be 60±3 Bq/l, and less than 0.13 Bq/l for radium, which were lower than the recommended levels set by WHO.     

238U, 235U, 137Cs and 133Xe in soils from two campuses in University of Douala—Cameroon

An evaluation of ²³⁸U, ²³⁵U, ¹³⁷Cs and ¹³³Xe in soils from two campuses in University of Douala—Cameroon using gamma spectroscopy based Broad Energy Germanium Detector (BEGe6530) has been performed. The mean activities in soils from Campuse 1 were 40.16±8.98 Bq/kg for ²³⁸U, 3.39±0.33 Bq/kg for ²³⁵U, 0.46±0.33 Bq/kg for ¹³⁷Cs and 0.14±0.16 Bq/kg for ¹³³Xe. In Campus 2, the mean activities in soils were 31.45±12.24 Bq/kg, 3.02±1.00 Bq/kg, 0.30±0.26 Bq/kg and 0.35±0.24 Bq/kg for ²³⁸U, ²³⁵U, ¹³⁷Cs and ¹³³Xe, respectively. Using the in situ survey meter, the mean values of the absorbed dose rate measured was 71.43 nGy/h for Campus 1 and 62.72 nGy/h for Campus 2. The evaluated average outdoor effective dose for Campus 1 and 2 were 87.60 µSv/yr and 76.93 µSv/yr, respectively. The overall results obtained in this work were generally low compared to that of UNSCEAR.     

Uranium series disequilibria in ground waters from a fractured bedrock aquifer (Morungaba Granitoids-Southern Brazil): Implications to the hydrochemical behavior of dissolved U and Ra.

Activity concentrations of dissolved (234)U, (238)U, (226)Ra and (228)Ra were determined in ground waters from two deep wells drilled in Morungaba Granitoids (Southern Brazil). Sampling was done monthly for little longer than 1 year. Significant disequilibrium between (238)U, (234)U and (226)Ra were observed in all samples. The variation of (238)U and (234)U activity concentrations and (234)U/(238)U activity ratios is related to seasonal changes. Although the distance between the two wells is short (about 900m), systematic differences of activity concentrations of U isotopes, as well as of (234)U/(238)U, (226)Ra/(234)U and (228)Ra/(226)Ra activity ratios were noticed, indicating distinct host rock-water interactions. Slightly acidic ground water percolation through heterogeneous host rock, associated with different recharge processes, may explain uranium and radium isotope behavior.     

Low-level γ-ray spectrometry at the underground laboratory Garching

Two low-background setups for material screening based on HPGe detectors were built in the Garching Underground Laboratory with an overburden of ~10 m.w.e. They include several layers of passive shielding as well as an active muon veto. The first setup (GEM) comprises a 150% efficiency HPGe detector which can optionally be surrounded by a NaI(Tl) scintillation detector that serves as anti-Compton veto. The second setup (LoAx) consists of two smaller HPGe detectors which are arranged face-to-face to cover a larger solid angle around the sample and to allow coincidence measurements.For a 5.6 kg piece of copper after 11 days of measurement we have reached a sensitivity for ²²⁶Ra and ²²⁸Ra/²²⁸Th of ~5 mBq kg⁻¹ with the GEM setup. In the LoAx setup we have achieved limits of less than 100 mBq kg⁻¹ for ²³⁴Th and ²¹⁰Pb with a 156 g sample of PPO wavelength shifter after 18 days of measurement.     

Spectral interference corrections for the measurement of 238U in materials rich in thorium by a high resolution γ-ray spectrometry

In this study, the spectral interferences are investigated for the analytical peaks at 63.3 keV of ²³⁴Th and 1001.0 keV of ^234mPa, which are often used in the measurement of ²³⁸U activity by the γ-ray spectrometry. The correction methods are suggested to estimate the net peak areas of the γ-rays overlapping the analytical peaks, due to the contribution of ²³²Th that may not be negligible in materials rich in natural thorium. The activity results for the certified reference materials (CRMs) containing U and Th were measured with a well type Ge detector. The self-absorption and true coincidence-summing (TCS) effects were also taken into account in the measurements. It is found that ignoring the contributions of the interference γ-rays of ²³²Th and ²³⁵U to the mixed peak at 63.3 keV of ²³⁴Th (²³⁸U) leads to the remarkably large systematic influence of 0.8–122% in the measured ²³⁸U activity, but in case of ignoring the contribution of ²³²Th via the interference γ-ray at 1000.7 keV of ²²⁸Ac to the mixed peak at 1001 keV of ^234mPa (²³⁸U) results in relatively smaller systematic influence of 0.05–3%, depending on thorium contents in the samples. The present results showed that the necessary correction for the spectral interferences besides self-absorption and TCS effects is also very important to obtain more accurate ²³⁸U activity results. Additionally, if one ignores the contribution of ²³²Th to both ²³⁸U and ⁴⁰K activities in materials, the maximum systematic influence on the effective radiation dose is estimated to be ~6% and ~1% via the analytical peaks at 63.3 and 1001 keV for measurement of the ²³⁸U activity, respectively.     

Development of a rapid source preparation method for high-resolution α-particle spectrometry

In order to prepare sources of short-lived actinides for α-particle spectrometry, a coprecipitation method with Sm hydroxide was developed. The preparation procedure can be completed within 5 min with a high chemical yield of over 90%. It was found that the uniformity of the produced sources was sufficient to provide a high resolution of better than 20 keV. Under this method, we successfully measured the α-particle spectrum of short-lived Cf isotopes produced in the ²³⁸U(¹²C, xn) reaction.     

A magnet system for the suppression of conversion electrons in alpha spectrometry

A new magnet system has been designed and constructed to reduce coincidence effects between alpha particles and conversion electrons in high-resolution alpha-particle spectrometry. By means of a magnetic field, the conversion electrons are deflected away from the PIPS^® detector. Compared to existing magnet systems, the new system is not restricted to point sources and can accommodate source diameters up to about 30 mm. Two yokes were built, allowing for configurations with 20 mm or 36 mm distance between the magnets. The effectiveness of both configurations is demonstrated by measuring the conversion electron spectrum of a ²³⁷Np source. The magnet system effectively rejects 93 (7)% of electrons up to 85 keV (36 mm) and 90 (9)% of electrons up to 320 keV (20 mm). It has been successfully applied in the alpha-particle spectrometry of the long-lived nuclides ²³⁶U and ²³⁸U, resulting in significant improvement of the accuracy of alpha emission probabilities.     

Indoor 222Rn measurements using an activated charcoal detector

A commercially available activated charcoal detector for measuring ²²²Rn activity concentrations in air was calibrated with known amounts of ²²²Rn and examined in terms of air luminescence counts and interferences from ²²⁰Rn and ²¹⁹Rn. The results for conditions normally encountered indoor indicate that the detector is simple and reliable. The method has been applied to assay indoor ²²²Rn activity concentrations in 387 homes in Tokyo and the adjacent four prefectures, which ranged from 0.7 to 140 Bq/m³ and averaged 22.7 Bq/m³.