1. I.K. MacKenzie, T.L. Khoo, A.B. McDonald, B.T.A. McKee: Phys. Rev. Lett. 19, 946 (1967)
2. See for example R.M. Nieminen: In Positron Solid State Physics, ed. by W. Brandt, A. Dupasquier (North-Holland, Amsterdam 1983) p. 359
3. W. Brandt, M. Mourino: Bull. Am. Phys. Soc. 24, 72 (1979)
4. I.K. MacKenzie, P.Z. Ghorayshi: Solid State Commun. 55, 125 (1985)
5. J.E. Ball: Thermally activated positron motion in paraffin wax, etc., Masters Thesis, Univ. Guelph (1987)