Robert J. Liefeld, 1968, Soft X-Ray Band Spectra
A. F. Burr, 1968, Bull. Am. Phys. Soc., 13, 576
A. F. Burr, 1969, Dev. Appl. Spec. A, 7, 121
M. B. Chamberlain, 1970, Bull. Am. Phys. Soc., 15, 560
M. B. Chamberlain, Phys. Rev. A
Robert R. Turtle, 1973, Phys. Rev. B, 7, 3411, 10.1103/PhysRevB.7.3411