Characteristic X-ray flux from sealed Cr, Cu, Mo, Ag and W tubes

The flux of characteristic Kα radiation from sealed X-ray tubes with Cr, Cu, Mo, Ag and W targets is determined on an absolute scale by measuring integrated intensities of Bragg reflections from well characterized powder samples. The values of the flux are corrected for absorption in the tube target. The tube voltage is varied, and the flux is observed to vary as (U₀−1)^p, where U₀ is the ratio of tube voltage to the excitation voltage of characteristic Kα radiation (over-voltage). The exponent p is very close to the theoretical value of 1.67 in the cases of Cr, Cu, Mo and Ag, while in the case of W the value of p is 1.45. The absolute values of the flux are close to the theoretical estimates of Green & Cosslett [Proc. Phys. Soc. (London) (1961), 78, 1206–1214] for Cr and Cu, 10 to 20% higher for Mo and Ag, but only about 1/3 of the calculated flux of W Kα radiation. This is due to an inadequate calculation of the indirect production of characteristic X-rays. A simple formula for the flux per unit solid angle is given in terms of the atomic number of the target, the tube voltage and the K excitation voltage.