On the velocity of the cathode rays ejected by substances exposed to the γ-rays of radium

The cathode radiation from a substance exposed to theγ -rays of radium consists, as is well known, partly of rays of a very penetrating character. Thus Eve found that the secondary rays from a lead plate, which in his experiments were deflected by a strong magnet into an ionisation chamber, possessed approximately the same penetrating power as theβ -rays of uranium. He tested the penetrating power of these deflected rays by placing successively different thicknesses of aluminium foil over the opening of the chamber and measuring the changes produced in the leak. This paper gives an account of some experiments of a more elaborate character by the writer on the subject. Two different methods were used in these experiments. One of the methods consisted in measuring the scattering of the cathode particles produced by different thicknesses of metal foil placed in the path of the rays. In the other method the cathode rays were deflected into an ionisation chamber by means of a strong electromagnet, and the ionisation in the chamber measured for magnetic fields of different strengths.