1. M. J. Seaton,Atomic and Molecular Processes, edited by D. R. Bates (Academic Press, Inc., New York, 1962), chap XI.
2. C. W. Allen,Astrophysical Quantities(The Athlone Press, London, 1955), p. 77.
3. A. C. G. Mitchell and M. W. Zemansky,Resonance Radiation and Excited Atoms(Cambridge University Press, Cambridge, 1934), p. 258.
4. In natural barium, 83% of all atoms are even-even isotopes which have no nuclear-spin hyperfine structure.
5. H. E. White,Introduction to Atomic Spectra(McGraw-Hill Book Co., New York, 1934), p. 160.