1. Association EURATOM-MEC-Romania, “Horia Hulubei” National Institute for Physics and Nuclear Engineering, P.O.Box MG-6, 76900 Bucharest, Romania
2. Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
3. Hahn-Meitner-Institut, Glienicker Strasse 100, 14109 Berlin, Germany
4. European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg, B-2440 Geel, Belgium