Depth Distribution of Origins of Characteristic X-Rays from Thick Targets

If I is the intensity of any x-ray wave-length as observed in a direction making an angle φ with the face of the (thick) target in which the radiation originates, then ST=-1μ(dlogIdcscφ)_cscφ=0 is the depth of the centroid of the x-ray luminosity distribution in the target. This depth is greater than the effective mean depth of production by an amount which depends upon the angle of observation and the form of the luminosity distribution. For large angle observation of Ag Kα at 100 kv (and probably at any voltage) the two depths are identical within the errors of measurement. The distributions of x-ray luminosity with target depth for Ag Kα from a thick target are calculated for six tube potentials from 50 kv to 175 kv from the intensity observations of Webster, Hansen and Duveneck. There is as yet no theory of these distribution functions. The characteristics of the curves obtained are shown to be capable of fairly simple mathematical description and to be in harmony with certain physical checks.