The transmission of cathode rays through matter

Abstract

The experiments of this paper are the outcome of an attempt to discover whether cathode rays are selectively absorbed when their speed is sufficient to excite the radiation characteristic of the material they traverse. The general laws of absorption of cathode rays were elucidated many years ago by Lenard,* and the law which bears his name is expressed by the relation I = I 0 e -λx, where I 0 is the " intensity " of a beam of cathode rays incident on an absorbing sheet of thickness x , and I is the "intensity" of the emergent rays. The intensity, as measured by Lenard, was indicated by the brightness of a phosphorescent screen struck by the rays. In the above formula λis the absorption coefficient. For a definite initial speed of ray λ/ρ is constant, ρ being the density of the absorbing material, while for any material Lenard found that λ varied inversely as the fourth power of the speed the rays.