V.B Brudanin, N.I. Rukhadze, V.G. Egorov, Ch. Briancon, P. Beneš, T. Vylov, K.N. Gusev, F.A. Danevich, A.A. Klimenko, V.E. Kovalenko et al.: Search for double electron capture of 106Cd in TGV-2 experiment. Bulletin of the Russian Academy of Sciences: Physics 70(2), 316-321 (2006).