Deconvolution of liquid scintillation alpha spectra of mixtures of uranium and radium isotopes.

A method for the determination of uranium and radium isotopes in water samples is proposed. Liquid scintillation techniques were used for collecting alpha spectra, which were then analyzed by fitting the alpha peaks with overlapping Gaussians. The analysis can quantify the observed isotopes with accuracy depending on the activity of each isotope. In order to simulate the peaks with Gaussian normal distribution functions, the centroid of each peak as well as the full width at half maximum (FWHM) are required, as they depend on the quenching of the sample. For this purpose, samples with known activities of 226Ra and its decay products and also of the uranium isotopes 238U and 234U, at various quenching levels, were used to establish the correlation of the peaks' shift with the quench effect. In addition, the correlation of the FWHM with the centroid of a peak was determined, using the same procedure. Following the above analysis technique, an average of 97+/-2% of detection efficiency and a lower limit of detection of 8.2 mBq kg(-1) for alpha isotopes were achieved.

Efficiency of aluminum-pillared montmorillonite on the removal of cesium and copper from aqueous solutions.

Aluminum-pillared-layered montmorillonites (PILMs) were tested for their potential application in the removal of copper or cesium from aqueous solutions. By varying the initial conditions, several PILMs were prepared and characterized by means of X-ray fluorescence (XRF), proton induced gamma-ray emission (PIGE), X-ray diffraction (XRD) and sorption isotherms. Uptake of metals was studied by means of XRF spectrometry for copper sorption or gamma-ray spectrometry for cesium, using 137Cs as radiotracer. The sorption kinetics and capacity of PILMs were determined in relation to the effects of factors such as the initial metal concentration, initial pH of the solution and the presence of competitive cations. Kinetic studies showed that an equilibrium time of few minutes was needed for the adsorption of metal ions on PILMs. A pseudo-first-order equation was used to describe the sorption process for either copper or cesium. The most effective pH range for the removal of copper and cesium was found to be 4.0-6.0 and 3.0-8.0, respectively. Cesium sorption isotherms were best represented by a two-site Langmuir model while copper isotherms followed the Freundlich or the two-site Langmuir model. Cesium sorption experiments with inorganic or organic competitive cations as blocking agents revealed that the high selective sites of PILMs for cesium sorption (1-2% of total) are surface and edge sites in addition to interlayer exchange sites. In copper sorption, the two sites were determined as interlayer sites of PILMs after restoring their cation exchange capacity and sites associated with the pillar oxides.

Rapid screening of 90Sr activity in water and milk samples using Cherenkov radiation.

A method for screening 90Sr in milk samples is proposed. This method is based on a liquid scintillation technique taking advantage of Cherenkov radiation, which is produced in a liquid medium and then detected by the photomultipliers of a Liquid Scintillation Counter (LSC). Twenty millilitres of water and milk samples spiked with various concentrations of 90Sr/90Y in equilibrium were added in plastic vials and then were measured with an LSC (TriCarb 3170 TR/SL). The derived efficiencies were 49% for water samples and 14% for milk samples. The detection limit was 470 mBq L(-1)(90)Sr for water, without any pretreatment. Milk contains potassium, which also produces Cherenkov radiation due to the presence of 40K. For this reason, the interference of 40K in the measurements of 90Sr in milk samples was also investigated. The detection limit for milk was 1.7 Bq L(-1)90Sr.

Determination of 226Ra in aqueous solutions via sorption on thin films and alpha-spectrometry.

An improved spectrometric method to determine the 226Ra activity in aqueous solutions is described. The method involves two stages, a preconcentration stage of 226Ra sorption onto a thin manganese layer and a measurement stage using alpha-spectrometry. Manganese oxide thin films were prepared and characterized with X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses. The thin films were found to follow the XRD patterns and chemical formula of the K-birnessite layered exchanger. The preconcentration of radium was studied relative to the initial radium concentration, pH and salt concentrations. The preconcentration kinetics was studied as a function of manganese surface, solution volume and salt concentration. Extensive Monte Carlo calculations were performed to optimise the detection of alpha-particles. In this way, the thin film preparation procedure as well as the radium sorption and the measurement conditions were optimised and detection limits lower than 0.5 mBq L(-1) were obtained for 2d of procedure completion. The method was validated with IAEA standards and it was applied for the determination of 226Ra in bottled waters and also wastewaters from the major thermoelectric plant in Greece. Moreover, the 226Ra distribution coefficients (K(d)) of two differently prepared powder manganese oxides, a crystalline silicotitanate and an aluminium-pillared montmorillonite were determined by gamma-spectrometry. 226Ra sorption experiments on silicotitanate thin films were performed and improvements in resolution and reduction of exposure time were observed.

Soil gas radon: a tool for exploring active fault zones.

The profile of soil gas radon was monitored in five active fault sites in northern and northwestern Greece. Measurements were carried out during summer months, using CR-39 solid state nuclear track detectors (SSNTDs). The spatial distribution of radon along lines traversing the fault zones revealed anomalies, clearly connected to the local tectonic structure. Specifically, increased radon signals evolved on the radon background level, in the vicinity of the faults' axes and the signal-to-background ratio ranged from 2 to 13. The consistency of this pattern confirms that the radon technique is powerful in the detection and mapping of active fault zones.

Reduction of cesium concentration in ovine tissues following treatment with Prussian Blue labeled with 59Fe.

The effectiveness of Prussian Blue in reducing the radiocesium contamination in ovine tissues was investigated. Five ewes were fed 137Cs-contaminated wheat for 30 d. When the 137Cs concentration in milk had reached equilibrium, one animal, serving as the control, was slaughtered and the activity in its tissues was measured. Two ewes were offered daily 1 g of Prussian Blue labeled with 59Fe in the Fe(III) position, outside the complex anion. One week after the administration of Prussian Blue, these animals were slaughtered, 1 wk apart, and the level of 137Cs in their tissues was measured. Comparing the concentration of 137Cs in the blood and tissues of the Prussian Blue treated animals to the corresponding concentrations measured in the control, a considerable reduction in the radiocesium activity concentration is observed. However, 137Cs concentrations are maintained at non-zero (about 20%) values in the first 2 wk after the administration of Prussian Blue. This observation can be attributed to the fact that most of 137Cs binds to Prussian Blue in the animals' digestive tracts and the measured activity concentrations follow the elimination of cesium from tissues. Using a two-compartment mathematical model, we can predict the level of 137Cs in tissue, following the administration of Prussian Blue. Labeling Prussian Blue in the Fe(III)-position resulted in the measurement of a (2.4 +/- 0.02) % retention of Fe(III) in sheep.

Ratios of transfer coefficients for radiocesium transport in ruminants.

A corollary of the multiple-compartment model for the transport of trace elements through animals was tested for cows, goats, and sheep. According to this corollary, for a given body "compartment" k of the animal (soft tissue, lung, liver, etc.), the ratio a(k) = f(k)/f(blood) of the transfer coefficients f, should exhibit similar values for physiologically similar animals. In order to verify this prediction, two experiments were performed at the Agricultural Research Station of Ioannina and at the facilities of Ria Pripyat in Pripyat, Ukraine. Eight animals in the first experiment and eighteen in the second were housed in individual pens and were artificially contaminated with a constant daily dose of radiocesium until equilibrium was reached. The animals were then sacrificed and transfer coefficients f(k) to twelve body "compartments" k were measured. These data were used to calculate the ratios a(k). The results were in accordance with predictions of the model and average values of a(k) were extracted for ruminants. It is concluded that these values may be employed for the prediction of animal contamination in any body compartment through the measurement of blood samples.

Kinetics of radiocesium sorption in lake sediments.

The sorption of radiocesium (137Cs) in sediments sampled from Lake Pamvotis of Ioannina was studied in a laboratory simulation. In a series of experiments, the kinetics of 137Cs sorption and 137Cs distribution profiles in sediment cores were investigated. The results have shown that a significant percentage of 137Cs (35%) is adsorbed in the sediments during the first 3 d, at a rate of 0.41 +/- 0.05 d-1. The rest of 137Cs is adsorbed with the slower rate of 0.024 +/- 0.004 d-1. 137Cs rapidly reaches (< 5 d) a depth that does not exceed 3.5 cm. The sorption of 137Cs was found to follow Freundlich's empirical law, which describes the adsorption of most substances in solution to solids.

Radiocaesium transfer to sheep's milk as a result of soil ingestion.

Soil ingestion as a source of radiocaesium contamination to ruminants was studied by measuring the transfer coefficient to sheep milk. Eight lactating ewes, housed in individual metabolism cages, were used. Fifty grams per day of heavily contaminated sandy topsoil, collected in 1990 from the Chernobyl area, were administered orally to the animals for a period of 1 week. The daily dose intake in 137Cs was 1835 Bq day-1. During this contamination period, daily milk production and excreta output were measured. The ewes were monitored for an additional 7 day decontamination period, while they fed on uncontaminated feed. Transfer coefficients were obtained through a best fit (minimum chi 2) of the data to predictions of a linear compartment model. The values obtained were fm = (2.6 +/- 0.7) x 10(-2) and f mu = (5 +/- 2) x 10(-2) days kg-1 for radiocaesium transport to milk and urine, respectively. These results suggest that soil ingestion can be a major source of radiocontamination for sheep and other free-grazing ruminants. Comparison of our results with soil-to-milk transfer coefficient values derived in two recent independent experiments suggests that there might be a strong dependence of radiocaesium availability on soil composition.