J. L. Aguado

A dosimetric model for determining the effectiveness of soil covers for phosphogypsum waste piles

Phosphogypsum (PG) is a by-product of the phosphoric acid production process that contains high concentrations of U-series radionuclides. PG piles formed during the last 30 years cover about 1,200 hectares and are located close to the town of Huelva (Spain) on a salt-marsh. The regional government of Andalusia restored the area beginning in 1990 by covering it with a 25-cm-thick layer of natural soil. With this restoration, the external gamma-dose rate in the zone has decreased drastically, approaching near environmental background values. This conclusion is based on results obtained through in-situ monitoring measurements and through a dosimetric model developed for that particular radiation source. As the model uses average parameters of the studied site, its output does not show a correlation point by point with the in-situ monitoring measurements. However, a good agreement is observed in average values over the covered piles. The model gives an average dose rate of 0.41 mGy y(-1) and the in situ monitoring 0.40 mGy y(-1). Based on this model, it is possible to calculate the necessary thickness of soil to reduce the dosimetric contribution from a similar extension of PG until the desired level is reached. In our conditions, in a 25-cm-thick soil, about 0.19 mGy y(-1) is the increase produced by the PG layer in relation to an infinitum soil layer. Consequently, no radiological concern exists in the restored zones with respect to the external gamma radiation.

A simple method for efficiency calibration of HPGe detectors in γ-spectrometric measurements

Abstract In this paper a simple, rapid and general method for γ -ray efficiency calibration of Ge detectors for environmental samples is presented. This method is based on the use of an active natural solid sample with several γ -emissions (in our case, 226 Ra) as the calibrating matrix for determining the full energy peak efficiency (FEPE) e c vs γ -emission energy E γ and the sample height h in a counting cylindrical geometry. The 226 Ra activity concentration is determined by α -particle spectrometry, a method that has previously been validated.

Ra and U isotopes determination in phosphogypsum leachates by alpha-particle spectrometry

Publisher Summary Forced leaching experiments on phosphogypsum reveals that the main transfer of Ra and U from the phosphogypsum wastes to the water performed with fresh phosphogypsum. Consequently, waters used for phosphogypsum transportation to the piles for its storage could be enriched in U-isotopes and 226 Ra. Additionally, U concentrations in these leachates were higher than for Ra, in agreement with the results found in sediments collected in the Tinto river, just in the zone where these waters drained after phosphogypsum storage. These sediments show U/Ra activity ratios higher than one, in contrast to the U/Ra activity ratios lower than one found in bulk phosphogypsum. On the other hand, leachates obtained from forced leaching experiments with phosphogypsum previously washed and stored in the piles (“old” phosphogypsum) showed for both U and Ra very low transfer to the waters.

Efficiency calibration for 210Pb gamma-spectrometric determinations in sediment samples

Publisher Summary A method of efficiency calibration for 210 Pb determinations by gamma-ray spectrometry in sediment samples is outlined. This method, developed for a cylindrical sample geometry with coaxial Ge detectors, is based on the gamma transmission method. It accounts for variable sample height and supplies a fundamental advantage: individual self-absorption corrections can be easily determined knowing the apparent densities and the elemental composition of the samples. This calibration has been used for dating sediments of the Huelva estuary (southwest of Spain). The results obtained by the application of the proposed calibration method to superficial sediments shows good agreement with those obtained by alpha-particle spectrometry. This fact validates it. Additionally, this calibration has been used successfully for dating sediment cores through the application of the 210 Pb method.

Sub-barrier Fusion and Breakup of Light Halo Nuclei

In this work we present new data for the sub‐barrier fusion of the system 6He+206Pb obtained in the Centre de Recherches du Cyclotron (UCL), in Louvain‐la‐Neuve, Belgium. The preliminary results suggest the absence of fusion enhancement at sub‐barrier energies.