The complete affiliation of the authors is the following:

M. Benedetti Department of Materials Engineering and Industrial Technologies and Italian Institute of Nuclear Physics INFN, University of Trento, 38050 Trento, Italy e-mail: matteo.benedetti@ing.unitn.it D. Bortoluzzi Department of Mechanical and Structural Engineering and Italian Institute of Nuclear Physics INFN, University of Trento, 38050 Trento, Italy S. Vitale Department of Physics, University of Trento and Italian Institute of Nuclear Physics INFN, 38050 Trento, Italy