226Ra, 228Ra and 228Th in scale and sludge samples from the Campos Basin oilfield E&P activities

More than 40 scale and sludge samples from the Campos Basin oilfield were analysed in terms of 226Ra, 228Ra and 228Th. Although the exact origin of the samples was not known, scale samples derived from production pipes and sludge samples from water-oil separation units. Reported values ranged from 0.13 to 331 kBq.kg(-1) for 226Ra, from 0.10 to 245 kBq.kg(-1) for 228Ra and <0.10 to 272 kBq.kg(-1) for 228Th in sludge samples. The concentrations in scales were much more regular than in sludges and ranged from 16.2 to 93.2 kBq.kg(-1) for 226Ra, from 4.0 to 36.9 kBq.kg(-1) for 228Ra and from 4.5 to 18.5 kBq.kg(-1) for 228Th. Based on the Basic Safety Standards recommendations and on the derived results, these activities cannot be regarded as exempted and specific procedures should be designed for their radiological control.     

210Pb, 210Po, 226Ra, U and Th in arable crops and ovine liver: variations in concentrations in the United Kingdom and resultant doses

Concentrations of a range of naturally occurring radionuclides have been determined in the same crops grown at two sites in the UK. Ovine liver has also been studied. One site was in an area where concentrations in soil are typical of the UK (the 'control' site) and the other in an area where levels were well above average (the 'test' site). For an average adult consumer of all of the foodstuffs studied, the doses from consumption for the test site were about 4 times higher than those for the control site. However, the differences were small compared with the variability in overall doses from natural background across the UK. 210Pb and 210Po were important contributors to doses for both sites, but at the test site the contribution from 226Ra was also significant. Of the foodstuffs studied, consumption of leafy vegetables and liver gave the highest doses. The doses from leafy vegetables were sensitive to the weather conditions prior to harvesting. Consequently, rigorous monitoring programmes should be based on several samples collected throughout the year; extrapolations based on a single annual sample are unlikely to be reliable.     

238U, 226Ra, 210Po concentrations of bottled mineral waters in Hungary and their committed effective dose

Nowadays the consumption of bottled mineral waters has become very popular. The average consumption of these is 0.36 l d(-1) per person in Europe. A considerable segment of the population drinks almost only mineral water as drinking water, which is about 1 l d(-1). As is known, some kinds of mineral waters contain naturally occurring radionuclides in higher concentration than the usual drinking (tap) water. The WHO (1993) legislation concerning the drinking waters does not include the mineral waters. In our work, the concentrations of (226)Ra, (238)U and (210)Po were determined in mineral waters available in Hungary. To determine the (226)Ra concentration the emanation method was used. The (238)U and (210)Po concentrations were determined by alpha spectrometry using semiconductor detector. The dose contribution was calculated using the radionuclide concentrations and the dose conversion factors from the Basic Safety Standard IAEA (1995), for 1 l d(-1) mineral water consumption. In some cases the calculated doses were considerable higher than the limit for drinking waters. Especially for children the doses can be remarkably high.     

Determination of specific activity of 226Ra, 232Th and 40K for assessment of environmental hazards

Studies have been carried out using gamma-spectrometric techniques to determine the natural radioactivity in some rocks that are used as building materials in Yemen. The concentrations of the natural radionuclides namely(226) Ra, (232)Th and (40)K in the rock samples collected from different rock markets in Yemen have been determined using an NaI(Tl) detector. The concentrations of (226)Ra, (232)Th and (40)K in the studied rock samples range from 22.2 to 88.8 Bq kg(-1), 8.12 to 113.68 Bq kg(-1) and 31.3 to 2222.3 Bq kg(-1), respectively. The concentrations of these radionuclides are compared with the typical world values. To evaluate the radiological hazard of the natural radioactivity, the radium equivalent activity, the air absorbed dose rate, the annual effective dose rate, the representative level index and the values of both external and internal hazard indices were evaluated and compared with the internationally approved values. The radium equivalent activity values of all rock samples are lower than the limit of 370 Bq kg(-1) except for one sample which is about 413.386. The values of external hazard index (H(ex)) and internal hazard index (H(in)), absorbed doses in indoor air and the corresponding effective dose equivalents in a typical dwelling are presented. The need for further studies is also discussed.     

Extensive radioactive characterization of a phosphogypsum stack in SW Spain: 226Ra, 238U, 210Po concentrations and 222Rn exhalation rate

Phosphogypsum (PG) is a by-product of the phosphate fertilizer industries that contains relatively high concentrations of uranium series radionuclides. The US-EPA regulates the agriculture use of PG, attending to its (226)Ra content and to the (222)Rn exhalation rate from inactive stacks. Measurements of (222)Rn exhalation rates in PG stacks typically show a large and still poorly understood spatial and temporal variability, and the published data are scarce. This work studies an inactive PG stack in SW Spain of about 0.5 km(2) from where PG can be extracted for agriculture uses, and an agriculture soil 75 km apart, being representative of the farms to be amended with PG. Activity concentrations of (226)Ra, (238)U and (210)Po have been measured in 30 PG samples (0-90 cm horizon) allowing for the construction of maps with spatial distributions in the PG stack and for the characterization of the associated PG inputs to agriculture soils. Averaged (226)Ra concentrations for the stack were 730+/-60 Bq kg(-1) (d.w.), over the US-EPA limit of 370 Bq kg(-1). (222)Rn exhalation rate has been measured by the charcoal canister method in 49 sampling points with 3 canisters per sampling point. Values in PG stack were under the US-EPA limit of 2600 Bq m(-2)h(-1), but they were one order of magnitude higher than those found in the agriculture soil. Variability in radon emissions has been studied at different spatial scales. Radon exhalation rates were correlated with (226)Ra concentrations and daily potential evapotranspiration (ETo). They increased with ETo in agriculture soils, but showed an opposite behaviour in the PG stack.     

Assessment of annual effective dose from 238U and 226Ra due to consumption of foodstuffs by inhabitants of Tehran city, Iran

The concentrations of (238)U and (226)Ra were determined in different foodstuffs purchased from markets in Tehran. Determinations of the radionuclides have been carried out using alpha spectrometry technique, on samples of egg, lentil, potato, rice, soya, spinach, tea and wheat. Average concentrations of natural radionuclides and foodstuff consumption rate were used to assess annual intake and based on intake values, the annual effective ingestion dose has been estimated for Tehran city residents. The measurement results show that soya has the maximum concentration of (238)U equal to 15.6 +/- 2.6 mBq kg(-1) and tea has the maximum concentration of (226)Ra equal to 1153.3 +/- 265.3 mBq kg(-1). Besides, the maximum annual effective dose from (238)U and (226)Ra were assessed to be 2.88 x 10(-2) +/- 7.20 x 10(-3) and 2.15 +/- 0.54 muSv, respectively, from wheat samples.     

Vertical distributions of 137Cs, 40K, 232Th and 226Ra in soil samples from Istanbul and its environs, Turkey

Determining the distribution of natural and artificial radionuclides in soil profiles as well as the surface layer of the soil is necessary due to the fact that radionuclides can enter the food chain from deeper soil layers and also contaminate ground water. In the current study, the activity-depth profiles of (137)Cs were determined in soil samples from 20 sites in and around the city of Istanbul. Naturally occurring radionuclides were determined at 12 of the locations. Uncultivated soil samples were taken in six horizontal layers at each location. Activity concentrations were measured with a gamma spectrometer. The impacts of texture, organic matter and pH of the soil on the vertical distribution of the radionuclides were also studied. The average and standard deviations of (137)Cs and (40)K activity concentrations in soil at a depth of 5 cm were found to be 16.46±14.71 and 450.2±239.1 Bq kg(-1), respectively. The activity concentrations of (40)K, (232)Th and (226)Ra were distributed uniformly with regard to soil depth. The depth distribution of (137)Cs generally fitted a linear function. The study revealed that >20 y after the Chernobyl disaster of 1986, 55 % of (137)Cs still remains in the upper 10 cm of soil in the Istanbul environment.     

Specific Features of the 226Ra, 238U,and 232Th Distribution in the Surface Layer of Marine Sediments under the Conditions of Active Biosedimentation in the Arctic Front Zone

Radiochemistry - The distribution of natural radionuclides and organic matter in bottom sediments of the active biosedimentation zone on the section drawn through the arctic front of the North...     

Investigations on the activity concentrations of 238U, 226RA, 228RA, 210PB and 40K in Jordan phosphogypsum and fertilizers

The activity concentrations of naturally occurring radionuclides ((238)U, (226)Ra, (228)Ra, (210)Pb and (40)K) in Jordanian phosphate ore, fertilizer material and phosphogypsum piles were investigated. The results show the partitioning of radionuclides in fertilizer products and phosphogypsum piles. The outcome of this study will enrich the Jordanian radiological map database, and will be useful for an estimation of the radiological impact of this industrial complex on the immediate environment. The activity concentration of (210)Pb was found to vary from 95 +/- 8 to 129 +/- 8 Bq kg(-1) with a mean value of 111 +/- 14 Bq kg(-1) in fertilizer samples, and from 364 +/- 8 to 428 +/- 10 Bq kg(-1) with a mean value of 391 +/- 30 Bq kg(-1) in phosphogypsum samples; while in phosphate wet rock samples, it was found to vary between 621 +/- 9 and 637 +/- 10 Bq kg(-1), with a mean value of 628 +/- 7 Bq kg(-1). The activity concentration of (226)Ra in fertilizer samples (between 31 +/- 4 and 42 +/- 5 Bq kg(-1) with a mean value of 37 +/- 6 Bq kg(-1)) was found to be much smaller than the activity concentration of (226)Ra in phosphogypsum samples (between 302 +/- 8 and 442 +/- 8 Bq kg(-1) with a mean value of 376 +/- 62 Bq kg(-1)). In contrast, the activity concentration of (238)U in fertilizer samples (between 1011 +/- 13 and 1061 +/- 14 Bq kg(-1) with a mean value of 1033 +/- 22 Bq kg(-1)) was found to be much higher than the activity concentration of (238)U in phosphogypsum samples (between 14 +/- 5 and 37 +/- 7 Bq kg(-1) with a mean value of 22 +/- 11 Bq kg(-1)). This indicates that (210)Pb and (226)Ra show similar behaviour, and are concentrated in phosphogypsum piles. In addition, both isotopes enhanced the activity concentration in phosphogypsum piles, while (238)U enhanced the activity concentration in the fertilizer. Due to the radioactivity released from the phosphate rock processing plants into the environment, the highest collective dose commitment for the lungs was found to be 1.02 person nGy t(-1). Lung tissue also shows the highest effect due the presence of (226)Ra in the radioactive cloud (0.087 person nGy t(-1)).     

Development and validation of a technique for the determination of 226Ra and 228Ra by liquid scintillation in liquid samples

Radium isotopes are dispersed in the environment according to their physicochemical characteristics. Considering their long half-lives and radiological effects, (226)Ra and (228)Ra are very important issues in radiological protection. In Brazil, radium isotopes represent an exposure problem both in nuclear fuel cycle installations and in high natural radiation background areas. The experimental part of this work includes the development of a technique for the determination of (226)Ra and (228)Ra by liquid scintillation with potential application in biological samples. Radium was concentrated and then separated from other constituents of the sample by co-precipitation/precipitation with Ba(Ra)SO(4). The precipitate was filtered and weighted to calculate the chemical yield. The filter containing the precipitate of Ba(Ra)SO(4) was transferred to a scintillation vial. Two methods were used to prepare the sources. The first one consisted of the addition of water (8 ml), Instagel XF (8 ml) and UltimaGold (4 ml) in the vial containing the filter and the precipitate, forming a gel suspension. In the second method, the precipitate was dissolved with 0.2 M ethylene-diamine-tetra-acetic-acid solution (9 ml) and 11 ml of scintillation solution (Optiphase Hisafe 3) was added to the vial, forming an aqueous and an organic phase. The solutions obtained were counted in a low background scintillation spectrometry system (Quantulus) suitable for the detection and identification of both alpha and beta particles for the determination of (226)Ra and (228)Ra. The activity values of (226)Ra and (228)Ra calculated by the two methods are in good agreement with the reference values, indicating that both methods are suitable for the determination of (226)Ra and (228)Ra.     

Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters

Kinetics of dissolution of (238)U, (234)U and (230)Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultrafiltrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolní Rozínka' at Rozná, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h(-1) and the sampling period is typically 1 month. Studied filters contained 125 +/- 6 mBq (238)U in equilibrium with (234)U and (230)Th; no (232)Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for (238)U and (234)U and slow dissolution half-times of 173 and 116 d were found for (238)U and (234)U, respectively. No detectable dissolution of (230)Th was found.     

Determination of 234U/238U ratio: comparison of multi-collector ICPMS and ICP-QMS for water, hair and nails samples, and comparison with alpha-spectrometry for water samples

The (234)U/(238)U ratio in water, hair and nails samples was determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) and inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and by alpha-spectrometry for the water samples only. A correlation of 0.99 was found between the two ICPMS methods and of 0.98 with alpha-spectrometry. The range of activity ratios was between 0.9 and 2.6 according to the MC-ICPMS measurements. The reproducibility of both ICPMS techniques was better than 4% for water samples containing 1 mug l(-1) of uranium and a (234)U/(238)U atom ratio of 54.9 x 10(-6). Sample preparation for the ICPMS consisted of dilution of water samples containing >10 microg l(-1) of uranium and measurement time was approximately 1 min, while alpha-spectrometry involved pre-concentration and separation of the uranium and counting times of 1,000 min.     

Separation and measurement techniques for the determination of 228Th, 230Th and 232Th in various matrices

Three analytical techniques are presented which are used at PSI for determination of U and Th isotopes (234U, 235U, 238U, 228Th, 230Th, 232Th) in different materials, i.e. environmental samples (soils, minerals) and dental ceramics as well as in urine for in vitro monitoring of potentially exposed workers. Depending on the sample quantity available and/or required detection limits the measurements are performed either directly via gamma spectrometry or via alpha particle counting with preceding separation chemistry. The separation methods applied are based on either extraction chromatography or on sorption of U and Th on actinide selective resin. Following sample digestion, chemical yield spike additions (232U, 225Th or 225Th), chemical purification and electro-depositional source preparation, alpha particle measurement is carried out using low-level alpha spectrometry. This technique allows detection limits of less than 0.2 mBq per counting source if the assay lasts over a few days and is therefore suitable for determination of trace quantities of short-lived 225Th that can be hardly detected by means of mass spectrometric techniques.     

Standard Reference Data on the Nuclear Characteristics of the Alpha-Radiating Radionuclides 226Ra, 233U, 238Pu,and 239Pu

Estimated values of the half-life, the energy and absolute emission probability of alpha-particles for radionuclides, forming part of the standard spectrometric alpha-radiation sources: ²²⁶Ra with daughter decay products ²³³U, ²³⁸Pu, and ²³⁹Pu, are presented as a draft of standard reference data. The recommended values are obtained by analyzing and selecting published estimated and experimental data (up to December 2000).     

Vertical distributions and gamma dose rates of 40K, 232Th, 238U and 137Cs in the selected forest soils in Izmir, Turkey

This paper presents the results obtained from a radioecological study carried out in the selected forest sites of Izmir, Turkey. The levels of gamma-emitting radionuclides, 40K, 232Th, 238U and 137Cs, in soils were determined using gamma spectroscopy. The activity profile for 40K, 232Th and 238U exhibits a uniform distribution with respect to depth. The depth distribution of 137Cs activity was established by fitting the experimental points to an exponential or a Gaussian function. About 42-97% of the 137Cs deposition was found in the first 10 cm of soil even after 18 y from Chernobyl accident. The dose-rate and annual-effective dose received from external irradiation were quantified. It is indicated that 137Cs from the fallout plays a less role in external radiation exposures in forest sites of Izmir than in potential exposures from naturally occurring radionuclides accounted for by soil.     

Vertical distribution of (226)Ra and (210)Po in agricultural soils in Buyuk Menderes Basin, Turkey

The vertical distribution of (226)Ra and (210)Po was investigated in the cultivated soils of the Buyuk Menderes Basin in Turkey. Five soil cores down to a depth of about 50 cm were taken from each site and divided into strata of 2-3 cm intervals. The samples were analyzed for their (226)Ra and (210)Po activity concentrations using radioanalytical methods. Down-core concentration profiles of (226)Ra and (210)Po in the soil cores from five sites are obtained. The activity concentrations of soil cores range from 80 to 1170 Bq kg(-1) for (226)Ra and from 10 to 870 Bq kg(-1) for (210)Po with the depth. Analysis of the vertical soil profiles indicate that the activity concentrations of (226)Ra and (210)Po for soil strata at all the sites have not extremely changed with depth.     

Calibration factors for determination of relativistic particle induced fission rates in U, U, Th, Pb and Au foils

Calibration factors w, for determination of fission rate in metallic foils of ^natU, ²³⁵U, ²³²Th, ^natPb and ¹⁹⁷Au were determined for foils in contact with synthetic mica track detectors. Proton-induced fission at proton energies of 0.7 GeV and 1.5 GeV were used. Using our experimental results as well as those of the other authors, w for different foil-mica systems were determined. Two methods were used to calculate w, relative to the calibration factor for uranium-mica system, which has been obtained in a standard neutron field of energy 14.7 MeV. One of these methods requires the knowledge of the mean range of the fission fragments in the foils of interest and other method needs information on the values of the fission cross-sections at the required energies as well as the density of the tracks recorded in the track detectors in contact with the foil surfaces. The obtained w-values were compared with Monte Carlo calculations and good agreements were found. It is shown that a calibration factor obtained at low energy neutron induced fissions in uranium isotopes deviates only by less than 10% from those obtained at relativistic proton induced fissions.