ABSTRACT
The nature of the αparticle from radioactive substances has, for several years, been one of the most important questions in Radioactivity. The evidence as a whole indicates that the αparticle is an atom of helium carrying a positive charge. This evidence is, however, of too indirect a character to prove decisively that the αparticle is an atom of helium. An experiment was then made to test whether the helium observed could have diffused from the emanation through the thin glass walls. In these experiments, every precaution was taken to prevent possible contamination of the apparatus with helium. Freshly distilled mercury and fresh glass apparatus was used. No trace of helium was observed in the outer tube over a period of eight days. Emanation was again introduced, and after four days, the helium spectrum was again observed. Other evidence indicates that the positive charge on the αparticle is twice that carried by the hydrogen atom.
