1. Bethe, H. A.: Rev. Mod. Phys. 9, 71 (1937).
2. Bethe, H. A.: Phys. Rev. 57, 1125 (1940).
3. Blatt, J. M., and V. F. Weisskopf: Theoretical Nuclear Physics. New York: John Wiley & Sons, Inc. 1952. This is a general reference for all phases of the subject through 1951.
4. Bohr, N., and F. Kalckar: Kgl. danske Vid. Selsk. mat.-fys. Medd. 14, 10 (1937).
5. Bohr, A., and B. R. Mottelson: Kgl. danske Vid. Selsk. mat.-fys. Medd. 27, 16 (1953), Appendix 5.