1. Department of Physics and Earth Sciences, University of Ferrara, Ferrara, Italy
2. Legnaro National Laboratory, INFN, Legnaro, Padova, Italy
3. INFN Ferrara section, Ferrara, Italy
4. INFN Padova section, Padova, Italy
5. Centre for GeoTechnologies, University of Siena, San Giovanni Valdarno, Arezzo, Italy
6. Department of Natural Science and Habitat, University of Sassari, Sassari, Italy