1. R. D. Craig, G. A. Errock, and J. D. Waldron, ?Advances in Mass Spectrometry?, edited by J. D. Waldron (Pergamon Press, Oxford, 1959).
2. R. Brown, R. D. Craig, and R. M. Elliott, ibid?, Vol. 2.
3. J. F. Duke, ?Ultrapurification of Semiconductor Materials? (Macmillan, London, 1962), p. 294.
4. R. K. Willardson, ibid?, p. 316.
5. R. Brown, R. D. Craig, and T. D. Waldron, ?Compound Semiconductors?, Vol. 1 (Reinhold, New York, 1962), p. 106.