[1] Univ Paris 11, Ctr Spectrometrie Nucl & Spectrometrie Masse, CNRS, F-91405 Orsay, France
[2] Univ Grenoble 1, CEA Grenoble, DRFMC Serv Phys Mat & Microstruct, F-38054 Grenoble, France
[3] FZ Rossendorf, Inst Ionenstrahlphys & Mat Forsch, D-01314 Dresden, Germany
[4] Univ Paris 11, Inst Elect Fondamentale, CNRS, F-91405 Orsay, France