The passage of cathode rays through matter

Abstract

When a beam of cathode rays strikes a sheet of matter, a portion of the beam is scattered back, a portion stopped by the matter and absorbed in it, and the remainder is transmitted. Similar effects, though on a different scale, are observed with other types of swift-moving electrified particles, and in the case of the a-rays their study has yielded valuable information as to the constitution of matter. In the case of the cathode rays, their much smaller penetrating power and the experimental difficulties have hindered accurate measurements of these processes. The writer has recently measured cathode ray absorption in a number of different metals, using rays of velocity from 0.20 to 0.40 of that of light. The main results were obtained by examining the true as well as the apparent absorption of the rays in passing through various thicknesses, where by true absorption is meant the fraction of the incident beam actually stopped by the matter, and by apparent absorption this fraction plus the fraction scattered back or “reflected.”