1. See for example,W. Heitler:The Quantum, Theory of Radiation (Oxford, 1954), 3rd ed., Sections 25 and 26;H. W. Koch andJ. W. Motz:Rev. Mod. Phys.,31, 920 (1959).
2. W. R. Johnson andC. J. Mullin:Phys. Rev.,119, 1270 (1960).
3. R. T. Deck, C. J. Mullin andC. L. Hammer:High frequency limit of the bremsstrahlung spectrum, to be published inPhys. Rev.
4. J. S. Pruitt andS. R. Domen: U.S. Department of Commerce, Natl. Bur. Standards Report 6218 (1958), and also Natl. Bur. Standards Monograph 48 (1962).
5. D. G. Keiffer andG. Parzen:Phys. Rev.,101, 1244 (1956).