A method is described for obtaining the distribution of energy in an x-ray beam as a function of wavelength. The method consists of obtaining filtration data with suitable filter material, and analyzing this data in terms of Laplace transforms. The desired distribution of energy is obtained in terms of a sum of inverse Laplace transforms.
M. A. GREENFIELD, R. D. SPECHT, P. M. KRATZ, and KATHERINE HAND, "Spectral Energy Distribution in X-Ray Beam as a Function of Wavelength," J. Opt. Soc. Am. 42, 6-11 (1952)