1. Pascal, P. (Nouveau Traité de Chimie Minérale, Vol. 9, Masson, Paris 1963, pp. 1141/2).
2. Bagnall, K. W. (The Actinide Elements, Elsevier, New York 1972, pp. 1/272).
3. Brown, D. (in (Bailar, J. C.; Emeléus, H. J.; Nyholm, R. S.; Trotman-Dickenson, A. F., Comprehensive Inorganic Chemistry, Vol. 5, Pergamon, Oxford 1973, pp. 277/86).
4. 6th Rare Earth Res. Conf., Gatlinburg, Tenn., 1967; N.S.A. 22 [1968] No. 23000).
5. Head, E.L. (Australian 426165 [1972]; N.S.A 28 [1973] No. 20856).