1. G.Balasse: Philips Res. Rep., Suppl.3, 91 (1964)
2. J.Tellier, M.Lensen: Bull. Soc. Chim. France1966, 2502
3. C.Zeller, J.Hubsch, J.Reithler, J.Bolfa: Compt. Rend.265, 1335 (1967)
4. W.O'Reilly, S.K.Banerjee. Phys. Letters17, 237 (1965)
5. R.Pauthenet, L.Bochirol: J. Phys. Radium12, 249 (1951)