S. Rizzo

Gamma activity and geochemical features of building materials: estimation of gamma dose rate and indoor radon levels in Sicily.

A high-purity germanium detector has been used to measure the abundance of radium (Ra), thorium (Th) and potassium (K) in building materials used in Sicilian dwellings. The measurements were performed to evaluate which material was suitable for the construction of an enclosure, which would have a low background emission. The materials examined in this work showed concentrations of 226Ra, 232Th and 40K dramatically variable depending on the lithologies, particularly in the case of blocks, sands and aggregates commonly used in building materials in Sicily. The results are discussed and a criterion is indicated to reduce the radiation dose to humans. Since radon inlet is a major health problem, all the radiometric data and the geochemical features have been used to determine the radon exhalation, which arises from the disintegration of 226Ra in soils and walls of houses. From our experimental data it can be seen out that one of the geochemical parameters, Total Alkali (TA), may be an appropriate index to select materials of low radiological risk.

Sediment delivery processes and the spatial distribution of caesium-137 in a small Sicilian basin

The sediment delivery processes occurring in a small Sicilian basin are modelled using the spatially distributed SEDD model recently proposed by Ferro and Minacapilli. The model is applied by using soil data (grain-size distribution, organic matter content, etc.) of 129 samples uniformly distributed over the study area and compiling the available information (topographic map, soil data, etc.) into a Geographical Information System. Finally, the predictive capability of the distributed sediment delivery approach is tested experimentally using the caesium-137 measurement technique. The comparison between calculated sediment yield and the corresponding measured caesium-137 loss is used to validate the SEDD model at the scale of both the single morphological unit and the entire basin.

Environmental radioactivity at Stromboli (Aeolian Islands).

HPGe gamma spectrometry, thermoluminescence dosimetry, X-ray diffractometry and fluorescence techniques have been used to analyze the natural radionuclides content of soil and rock samples, air kerma and geochemical features on the island of Stromboli, belonging to the Aeolian Islands, in the Mediterranean Sea. The 214Bi, 238Ac, and 40K contents obtained are in agreement with the magmatic evolution of the rock formation, as shown by the correlations between radionuclide and chemical elements abundacies, depending on the various magmatic differentiation mechanisms. Correlations between radiometric, lithological and geochemical data have been assessed in order to obtain some hints on the geochronology of the magmatic products.

Chemistry, mineralogy and radioactivity in posidonia oceanica meadows from North-Western Sicily

This paper presents measurements of major, minor, metal trace elements and radionuclides in sediments and in Posidonia oceanica samples from north-western Sicily (Italy). The mineralogical and chemical composition of sediments were determined by X-ray diffraction and X-ray fluorescence techniques, respectively. A flame atomic absorption spectrophotometry was used to measure concentrations of Cu, Zn, Cd and Pb in P. oceanica samples and in sediments. Specific activities of selected radionuclides have been determined by high-resolution gamma spectrometry. Standard statistical analysis was used to assess correlations between different elements and different sample types.

Seasonal variation of air kerma rate in Sicily.

Thermoluminescence dosimetry has been used to measure air kerma in 29 sites in Sicily. Four three month measurement campaigns have been carried out in order to assess seasonal variations. Average annual values between 20 and 90 nGy h(-1), after cosmic background subtraction, are reported. Average annual values are strongly dependent on site lithology, and we find that winter data are generally the highest, while spring and autumn rates are generally the lowest with very similar trends in any site. Summer values generally lay in between. Largest seasonal variations are found in sites along the southern coast of the island, probably because of stronger action of winds affecting radon, along with its progeny, concentrations at ground level.

Virtual point detector: application to coincidence-summing correction in gamma-ray spectrometry.

The use of an efficiency transfer method based on the virtual point detector approximation to evaluate coincidence-summing correction values for point and volume sources was examined. The method was validated by means of a comparison with experimental efficiency determinations.

Radionuclides in wastewater treatment plants: monitoring of Sicilian plants

Three Sicilian wastewater treatment plants were monitored to assess the occurrence and the behaviour of radionuclides. Two sampling campaigns (screening and long-term) were carried out during which liquid and solid samples have been analysed. It was found that ¹³¹I mostly occurred in the samples analysed during the screening campaign (43% of the analysed samples contained ¹³¹I). High ¹³¹I specific activity was found in the mixed liquor, recycled sludge and dehydrated sludge samples. This finding was mainly due to the tendency of (131)I to be associated with solid particles. During the long-term sampling campaign an influence of the sludge retention time (SRT) on the ¹³¹I behaviour was found. Increasing the SRT and consequently decreasing the fraction of active organic biomass inside the system, the specific activity of ¹³¹I decreases.

Assessing soil erosion in a small Sicilian basin by caesium-137 measurements and a simplified mass balance model

Abstract The caesium-137 technique affords both an alternative to conventional measurement methods and an effective quantitative estimate of soil redistribution at the basin scale. Among the available calibration relationships which link the degree of increase or depletion of the 137Cs activity relative to the baseline 137Cs input and sediment yield, the mass balance approach has received increased application for its physical basis. First, the applicability of the refined simplified point-based mass balance (RSPMB) model of Zhang et al. (1999) at the scale of the morphological unit is proposed herein. The 137Cs spatial distribution measured in a small Sicilian basin and the spatial distribution of the sediment yield calculated by a sediment delivery distributed approach are used to estimate values of the two key parameters of the RSPMB model, φ1 and φ2, the fraction of 137Cs fallout incorporated into soil and a particle size correction factor, respectively. Finally, the best procedure for experimental testing of a distributed sediment yield model by using caesium-137 measurements is investigated.