The Origin of K-Radiation from the Target of an X-Ray Tube

The fluorescent energy transformation coefficient, the ratio of the energy of secondary K-radiation emitted by an elementary volume of the radiator to the energy absorbed by it from the exciting x-rays, is observed for Fe, Ni, Cu, Zn, Mo, and Ag. The ratio of quanta emitted as K-radiation to quanta absorbed seems to be a constant for a given metal; Fe—33 percent; Ni—39 percent; Cu—43.5 percent; Zn—50 percent; Mo—83 percent; Ag—75 percent. Making use of the experimentally determined values of the transformation coefficient the fluorescent $K$-characteristic radiation from the target of an x-ray tube is calculated for Cu and Ag, and compared with observed values of the total K-radiation. An estimate is also made from theoretical considerations of the relative amounts of direct impact K-characteristic radiation to be expected from an x-ray tube target. The calculations indicate that for silver and probably for other elements of high atomic number practically all of the K-characteristic radiation from an x-ray tube is fluorescent in origin while for copper and probably other elements of low atomic number a considerable part of the K-radiation is due to direct impact of the cathode electrons.