Ionisation by alpha-particles in monatomic and diatomic gases

Abstract

Measurements of the total number of ions produced by alpha-particles in various gases have not hitherto given results which our ideas of ionisation-potential would lead us to expect. In 1899 Rutherford showed that the total ionisation due to alpha-particles from uranium in H 2 , N 2 , O 2 , CO 2 , HCl, and NH 3 , was nearly the same. Measurements on these and polyatomic gases have also been made by W. H. Bragg, Laby, Kleeman, and Hess and Hornyak. In a gas with a high ionisation-potential we should expect the total ionisation to be smaller than in a gas with a low ionisation-potential. Taylor, however, showed that in helium, which has an exceptionally high ionisation-potential, the total ionisation is greater than in hydrogen or air. It was thought that experiments on the other monatomic gases—xenon, krypton, argon, and neon—might throw light on this anomaly. This paper describes measurements on the five rare gases, which have yielded an intelligible result. Measurements have also been made on H 2 , O 2 , and N 2 .