Experiments on the Emission Quanta of Characteristic X-Rays

Abstract

TT has been assumed by many authors that Planck's quantum hypothe--*-sis when applied to the energy of cathode rays, would give the highest frequency of X-rays they could produce.The first accurate experimental proof of this law was given by Duane and Hunt 1 for the case of the general radiation from a tungsten target, and was extended to a cathode ray potential of no kv.by Hull. 2 Off hand one would expect the law to apply to characteristic rays also.The possibility that it does not is indicated by the fact that Whiddington 3 found that the total radiation from a metal exposed to X-rays begins to increase rapidly with increasing energy of the cathode electrons when their energy is nearly 40 per cent, above that which the quantum law was later found to demand for the production of the a lines, the strongest of the K series.A similar conclusion on X-rays from a metal exposed directly to cathode rays is indicated by some later work of Beatty. 4As the point where this occurs is not very definite and the interpretation of the results is uncertain, it seemed desirable to test each characteristic line alone with a spectrometer.A brief report of the principal results of such a test is contained in a paper which I presented to the American Physical Society in December, 1915, and published in the Proceedings of the National Academy in March, 1916.The purpose of the present paper is to report the results more fully and discuss in more detail their theoretical significance. APPARATUS.For this work I used a rhodium target in a tube which Dr.