The capture and loss of electrons by α-particles

In a recent paper the writer presented evidence of α-particles bearing a single positive charge and of α-particles which were neutral. These were found by deflecting α-particles by a magnetic field in a good vacuum and registering them photographically on Schumann plates. A band appeared on the plate deflected only half the amount of the regular a-particle band. This was ascribed to α-particles, which had captured electrons in passing through an absorbing screen and thus were singly-charged. The behaviour of these particles was described qualitatively. The proportion of singly- to doubly- charged particles increased rapidly as their velocity decreased. From the effects of air in the path of the α-particles it was suggested that each particle must capture and lose electrons many times. Sir E. Rutherford has recently published the results of a very interesting quantitative study of these particles by the scintillation method. By electrostatic deflection of the beam he showed that the particles undergoing only half the normal deflection must be singly-charged α-particles and nothing else. By counting methods he found values for the mean free paths for capture and for loss of an electron by the α-particle, and found the way in which these mean free paths varied with the velocity.