Some remarks concerning the production and absorption of soft X-rays and secondary electrons

In the present paper an attempt is made to estimate the efficiency of the production of photoelectrons from metals by soft X-rays. When due consideration is paid to the absorption of radiation and electrons in the target the number of photoelectrons for one quantum of radiation absorbed comes out of the order unity. This result in connection with efficiency measurements on soft X-ray production, using the photoelectric method, shows that the yield of such radiation, when metals are bombarded with electrons, is extremely small. A very much larger portion of the energy of the bombarding electrons, possibly all the rest of it, reappears in smaller units as energy of secondary electrons. The question as to the probable origin of these electrons is discussed; it appears most likely that at least a great part of these are initially free conduction electrons of the substance. Before the manuscript of this paper had been completed, a paper by Prof. O. W. Richardson appeared dealing chiefly with the same problems. Some of the results presented here have already been arrived at by the latter author. Since, however, my own reasoning in deriving these results differs in several respects from that of Prof. Richardson’s, I have decided to publish the present paper in its original form, in the hope that the different treatment would in itself present some points of interest.