1. A. Seeger, Phys. Letters53A (1975) 324
2. I.Ya. Dekhtyar, D.A. Levina, and V.S. Mikhalenkov, Vopr. Fiz. Metalloved. No. 19 (1964) 127
3. I.K. MacKenzie, T.L. Khoo, A.B. McDonald, and B.T.A. McKee, Phys. Rev. Letters19 (1967) 946
4. W. Brandt, in: Positron Annihilation, eds. A.T. Stewart and L.O. Roellig (Academic Press, New York and London, 1967) pp. 179–181
5. D.C. Connors and R.N. West, Phys. Letters30A (1969) 1203