1. A. J. Ahearn, 11th Ann. Conf. Mass Spectrometry, ASTM E-14, San Francisco, Cal., 1963, p. 223.
2. W. M. Hickam and G. G. Sweeney, 11th Ann. Conf. Mass Spectrometry, ASTM E-14, San Francisco, Cal., 1963, p. 319.
3. R. A. Wallace and J. Roboz, 11th Ann. Conf. Mass Spectrometry, ASTM E-14, San Francisco, Cal., 1963, p. 451.
4. E. Berkey and G. H. Morrison, Mater. Sci. Center Rep. 1129 (1969), Cornell Univ., Ithaca, N. Y.
5. R. E. Honig and J. R. Woolston, Appl. Phys. Lett.2, 138 (1963).