1. “Horia Hulubei”, National Institute for Physics and Nuclear Engineering IFIN HH, 407 Atomistilor street, 077125 Magurele Ilfov, Romania, e-mail: lidiamatei@nipne.ro
2. Tritium Laboratory, Forschungszentrum Karlsruhe, Postfach 3640 D 76021, Karlsruhe Germany
3. National R&D Institute for Cryogenics and Isotopic Technologies ICIT Rm Valcea, Valcea Romania