[1] P.A.M. Dirac , Proc. Combridge Philos. Soc., 26 (1930), 361.
[2] C.D. Andersen , Phys. Rev., 43 (1933), 497.
[3] W. Brande and A. Dupasquier eds., Positron solid-state physics. North-Holland , Amsterdam . 1983.
[4] P.G. Coleman et al . eds., Positron annihilation, North-Holland , Amsterdam , 1982.
[5] P.C. Jain et al . eds., Positron annihilation, World Sci. Pub. , Singapore . 1985.
[6] D.M. Schrader and Y.C. Jean eds., Positron and positronium chemistry, Elsevier Sci. pub. , 1988.
[7] Y.C. Jean et al ., Phys. Rev., B36 (1987). 3994;
[8] S.J. Wang and Y.C. Jean , Phys. Rev., B37(1988), 4689.
[9] S.J. Wang and Y.C. Jean , Chinese Phys. Lett., 5(1988), 557.
[10] S. Berko et al ., Anu. Rev. Nucl. Part. Sci., 30 (1980), 543.
[11] A. Rich , Rev. Mod. Phys., 53 (1981), 127.