1. D. Dew-Hughes: Bull. Am. Phys. Soc. Ser. II,20, 342 (1975)
2. See B.W. Roberts:Progress in Cryogenics, Vol. 4, ed. by K. Mendelssohn (Academic Press, Inc. N.Y. 1964) pp 159–231 and pertinent references therein
3. S. Geller: Acta Cryst.9, 885 (1956)
4. J.H. Carpenter, A.W. Searcy: J. Am. Chem. Soc.18, 207 (1956)
5. S. Geller: Unpublished, but recorded and witnessed (1956)