The photographic action of the α-particles emitted from radio-active substances

Abstract

It has been shown by Rutherford that the photographic action of α -particles stops suddenly when the thickness of an interposed aluminium screen is increased beyond a certain value. It is noticeable that the thickness of the screen required to completely stop photographic action is identical with that required to stop ionisation in gases and scintillations of a phosphorescent screen caused by α -particles. The first object of the present experiments was to investigate the manner in which the photographic action of α -particles varies along their path, and to see if there is any connection between this and the well-known variation of the ionisation produced in gases. This having been accomplished, a relation was found between the photometric density of the film produced on development and the number of α -particles incident upon it. Experiments were then made to see whether a single α -particle produced a detectable photographic effect.