Radiological characterization of the tailings of an abandoned copper mine using a neural network and geostatistical analysis through the Co-Kriging method.

The radiological characterization of soil contaminated with natural radionuclides enables the classification of the area under investigation, the optimization of laboratory measurements, and informed decision-making on potential site remediation. Neural networks (NN) are emerging as a new candidate for performing these tasks as an alternative to conventional geostatistical tools such as Co-Kriging. This study demonstrates the implementation of a NN for estimating radiological values such as ambient dose equivalent (H*(10)), surface activity and activity concentrations of natural radionuclides present in a waste dump of a Cu mine with a high level of natural radionuclides. The results obtained using a NN were compared with those estimated by Co-Kriging. Both models reproduced field measurements equivalently as a function of spatial coordinates. Similarly, the deviations from the reference concentration values obtained in the output layer of the NN were smaller than the deviations obtained from the multiple regression analysis (MRA), as indicated by the results of the root mean square error. Finally, the method validation showed that the estimation of radiological parameters based on their spatial coordinates faithfully reproduced the affected area. The estimation of the activity concentrations was less accurate for both the NN and MRA; however, both methods gave statistically comparable results for activity concentrations obtained by gamma spectrometry (Student's t-test and Fisher's F-test).

Influence of soil chemical composition on U, 226Ra and 210Pb uptake in leaves and fruits of Quercus ilex L.

To determine their transfer factors, activity concentrations of natural radionuclides were measured in the leaves and acorns of holm oak (Quercus ilex L.) trees collected from seven locations with different soil properties and radionuclide activity concentrations. The chemical and mineralogical compositions of the soils were also analysed to investigate the effect these had on radionuclide absorption by the trees. Soil chemistry showed significant effects on radionuclide incorporation into Quercus ilex L. tissues. A significant relationship was established between activity concentrations and soil content of Ca and P with 238U and 226Ra in the leaves and acorns of Quercus ilex L. Differentiated transfer was found for 40K, which showed greater transfer to the leaves than the other radionuclides. The activity concentration of U and 226Ra was higher in the fruits than in the leaves, with the opposite effect being observed for 40K. The risk of U and 226Ra transfer into the food chain through acorn consumption by livestock is predicted to increase in soils poor in Ca and rich in P.

Increasing the recovery and selectivity of 238U, 235U, and 234U extraction with tri-n-butyl phosphate in mine tailing samples with a high copper content.

Abandoned Cu mine tailings may be associated high concentrations of U. However, the presence of stable cations such as Cu, Fe, Al, Ca, or Mg, etc. in high concentrations can reduce the chemical efficiency of the liquid-liquid extraction method with tri-n-butyl phosphate (TBP); it can also inhibit the electrodeposition of U on the stainless steel planchet where the sample is measured. In this work we studied an initial stage of complexation with ethylenediaminetetraacetic acid (EDTA) and a back extraction with different solutions: H2O, Na2CO3, and (NH4)2CO3 at room temperature and at 80 °C. The sensitivity of the method was 4.9·10-4 Bq for 238U and 234U, and 2.3·10-5 Bq for 235U. The validation of the method achieved 95% of the results when using a |ζ-score| ≤ ± 2.0 and a relative bias (RB[%]) ≤ ± 20% as the acceptance criteria. The recoveries obtained with the proposed method were higher than those achieved with the extraction method without initial complexation and re-extraction with H2O for water samples. Finally, this method was applied in practice to study the tailing of an abandoned Cu mine and the activity concentrations of 238U and 235U were compared with those obtained by gamma spectrometry for 234Th and 235U. The means and variances of both methods showed no significant differences between these two isotopes.

Improvements in the radiochemical method for separating 226Ra in solid samples through coprecipitation with BaSO4.

The aim of this work was to improve the commonly used method for 226Ra determination in water and to establish its application in solid samples. This method is based on the coprecipitation of Ra with BaSO4 and gross alpha counting of the precipitate. An exhaustive study of the coprecipitation behaviour of the most abundant cations present in solid samples was performed to avoid incorrect radiochemical yields. As a result, it was considered necessary to introduce two new purification steps into the conventional method. Likewise, two nuclides, 241Am and 226Ra, were compared to obtain the mass efficiency curve given their different behaviour in the coprecipitation process. While Ra behaves similarly to Ba, Am coprecipitates, forming mixed crystals that may behave differently in the self-absorption process. The influence of the cations on the chemical yield with no precipitate purification was: Sr2+≫Fe3+>Mg2+≈Ca2+>K+≈Na+. The method was successfully applied to soil, sediment, and plant ash samples.

Uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes.

This paper studies the uranium content and uranium isotopic disequilibria as a tool to identify hydrogeochemical processes from 52 groundwater samples in the province of Granada (Betic Cordillera, southeastern Spain). According to the geological complexity of the zone, three groups of samples have been considered. In Group 1 (thermal waters; longest residence time), the average uranium content was 2.63 ± 0.16 µg/L, and 234U/238U activity ratios (AR) were the highest of all samples, averaging 1.92 ± 0.30. In Group 2 (mainly springs from carbonate aquifers; intermediate residence time), dissolved uranium presented an average value of 1.34 ± 0.13 µg/L, while AR average value was 1.38 ± 0.25. Group 3 comes from pumping wells in a highly anthropized alluvial aquifer. In this group, where the residence time of the groundwater is the shortest of the three, average uranium content was 5.28 ± 0.26 µg/L, and average AR is the lowest (1.17 ± 0.12). In addition, the high dissolved uranium value and the low AR brought to light the contribution of fertilizers (Group 3). In the three groups, 235U/238U activity ratios were similar to the natural value of 0.046. Therefore, 235U detected in the samples comes from natural sources. This study is completed with the determination of major ions and physicochemical parameters in the groundwater samples and the statistical analysis of the data by using the Principal Component Analysis. This calculation indicates the correlation between uranium isotopes and bicarbonate and nitrate anions.

NATURAL RADIUM ISOTOPES PRESENT IN SOME COSMETIC PRODUCTS: DETERMINATION OF ACTIVITY CONCENTRATION AND DOSE ESTIMATION.

Since the early days, clays, plant extracts and raw materials have been used for therapeutic and beauty purposes. Nowadays, this use is widely spread, as a huge amount of companies have developed new cosmetics based on natural sources. This may lead to an accumulation of radionuclides that can be hazardous for people. Especially dangerous are radium isotopes (226,228Ra), which can be part of the raw materials that cosmetics are made from. In this paper, the concentration of radium isotopes of 18 natural cosmetics was determined. Concentrations resulted in the range 7.9 ± 5.0-37.6 ± 12.5 Bq kg-1 for 226Ra; and 2.5 ± 1.7-35.4 ± 2.6 Bq kg-1 for 228Ra. The effective dose in the skin has been estimated, obtaining a mean value of 13.1 ± 4.9 µSv y-1. This value is far from the reference level of 50 mSv y-1 for the public members. Therefore, no radiological risk derived from the use of these samples, has been found.

DETERMINATION AND DOSE CONTRIBUTION OF URANIUM ISOTOPES AND 210Po ACTIVITY CONCENTRATIONS OF NATURAL SPRING WATERS IN THE PROVINCE OF GRANADA, SPAIN.

The activity concentrations of alpha-emitters comprising isotopes of uranium (238, 234, 235U) and polonium (210Po) were measured using alpha-particle spectrometry in natural spring waters in the province of Granada, Spain. These water are consumed by the population of the zone who live in villages. This is almost half of the population of the whole region. Mean values of activity concentrations found are 42.61 ± 2.66; 49.55 ± 3.03; 1.64 ± 0.28 and 1.74 ± 0.15 mBq L-1 for 238U, 234U, 235U and 210Po, respectively. Finally, the radiological impact of the analysed waters has been determined, in terms of the estimation of the committed annual effective dose due to the ingestion of the water. The assessment has been carried out for five age groups with the aim to cover all the population. The calculated annual effective doses are observed to be below the prescribed dose limit of 100 µSv y-1 recommended by WHO.