Bremsstrahlung emission from four x-ray tubes operating at 12 to 300 kV was measured. Spectral distributions are given in terms of absolute-photon and energy fluxes. Silicon and germanium semiconductors, sodium iodide scintillators, and a xenon proportional counter were used to measure the spectra. Detector distortions were corrected by assuming an undistorted spectrum, distorting the spectrum with a Monte Carlo computer program, and comparing the results with measurement. The assumed undistorted spectrum was revised until the Monte Carlo calculation gave satisfactory agreement with spectral measurements from all four types of detectors. The effects on the spectra of varying the tube potential, tube current, target aperture, and detector aperture were investigated. Corrections for the intervening material and the solid angle subtended by the detector were applied to obtain the absolute-photon and energy flux from the target. Total fluxes in the L lines, K lines, and continuum are given.
X-ray-production efficiencies varied from 0.026% at 12 kV to 1% at 300 kV. The constant of proportionality varied in the range (0.23 to 0.73) x 10-6 kV-1.