The ratio of characteristic to white X-radiation from a copper target

The ratio ( k ) of the total Kα radiation to the total white radiation emitted by copper target X-ray tubes has been estimated by isolating the contribution of wavelengths near λKα with balanced nickel and iron filters. The total radiations leaving the tube have been inferred from the counting rates of a Geiger counter exposed to the direct beam from the X-ray tube (suitably attenuated by a pinhole system). Corrections for transmission of the air path and quantum efficiency of the Geiger counter as functions of wavelength were applied to an assumed spectral distribution for the white radiation. The assumed spectral distribution was selected on the basis of a literature survey of investigations on continuous spectra, a brief outline of which is given. It is found that at 35 kVp, k = 2.2, a result which lies between those of Arndt and Riley, who found k = 5.4, and of Parrish and Kohler, from whose curves a value of k = 0.35 is deduced. A measure of reconciliation between these results is achieved if various corrections and different experimental conditions are taken into consideration. Curves show the variation of k over the target area, with take-off angle, and with voltage; the form of the voltage variation agrees with the results of Guinier.