1. I. Ahmad and W. Haider, J. Phys. G: Nucl. Phys. 2, L157 (1976).
2. N. Austern, Phys. Rev. 136, B1743 (1964).
3. N. Austern, Phys. Rev. 137, B752 (1965).
4. American Institute of Physics Conference Proceedings, Number 97;N Austern,1983
5. M. Baldo, I. Bombaci, L. Ferreira, G. Giansiracusa, and U. Lombardo, Phys. Lett. B209, 135 (1988).