1. I. Spirn, W. Brandt, G. Present andA. Schwarzschild:Bull. Am. Phys. Soc.,9, 394 (1964).
2. A. W. Sunyar:Bull. Am. Phys. Soc.,9, 394 (1964).
3. W. Brandt:Contribution to the Proceedings of Wayne Conference on Positron Annihilations, Detroit, 1965.
4. W. Brandt andI. Spirn:Phys. Rev.,142, 231 (1966).
5. M. Bertolaccini, C. Bussolati andL. Zappa:Phys. Rev.,139, A 696 (1965).