Bremsstrahlung radiation has been used to excite nearly monoenergetic x rays in secondary targets which can be utilized to study the energy response of radiation detectors if the intensity and purity are known. A method is suggested of calculating the spectral intensity of the secondary-target radiation, including the K-fluorescent x rays, and the bremsstrahlung plus characteristic-line radiation scattered from the target. Both coherent and incoherent scatter are included in the calculation. To test the theory, bremsstrahlung radiation from an x-ray unit operating in the 100–300-kV potential range was used to excite K-fluoresecent radiation in secondary targets ranging in atomic number from 29 to 90. Both the primary and secondary spectra were measured with NaI and germanium detectors. The measured primary spectral intensities were used as input to the secondary spectral intensity calculation. Calculated secondary spectra were within 20% agreement with measurement. Optimization of the secondary-target intensity and purity is discussed as a function of target thickness, potential, and selective filtration.