A Relation Between Line and Continuous X-Ray Spectra

It was discovered empirically by Webster that if an electron collides with a silver atom there is a constant ratio between the probability of ejection of a $K$-electron and the probability of emission of a continuous spectrum quantum of frequency between the critical $K$-absorption frequency and the high-frequency limit. Webster used voltages from 35 kv to 80 kv. The present work is on palladium and extends the voltage range to 180 kv; the same result holds. A step in the determination of the above ratio is to find the ratio $P$, for a thick target, of the amount of $K\alpha$ rays resulting from ionization by collision to that resulting from fluorescence. For palladium at normal emergence $P$ is found to be almost constant at 2 up to 180 kv. $P$ is needed in any comparison of the results of thin and thick target line emission experiments since in a truly thin target ionization is by collision only whereas in thick targets fluorescence is also important.