1. N. F. Mott, H. S. W. Massey: The Theory of Atomic Collisions (Clarendon Press, Oxford 1965) Chapt. IX
2. D. M. Fradkin, R. H. Good: Rev. Mod. Phys. 33, 343 (1961)
3. L. I. Schiff: Quantum Mechanics, 3rd ed. (McGraw Hill Book Co., New York 1968) Chapt. 13
4. H.A. Bethe, E. E. Salpeter: In Handbuch der Physik (Springer, Berlin-Göttingen-Heidelberg 1957) Vol. XXXV, p. 133ff.
5. H. F. Schopper: Weak Interactions and Nuclear Beta Decay (North-Holland Publ. Co., Amsterdam 1966);