1. European Communities, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel, Belgium
2. Ghent University, Department of Subatomic and Radiation Physics Proeftuinstraat 86, B-9000 Gent, Belgium
3. CEA-Cadarache, DEN/DER/SPRC/LEPh, F-13108 Saint Paul lez Durance, France
4. SCK-CEN, Boeretang 200, B-2400 Mol, Belgium