A determination of the absolute velocity of the alpha-particles from radium C'

Abstract

The first accurate determination of the velocity of expulsion of the α-particles from radioactive substances was made by Rutherford and Robinson, who, by measuring magnetic and electric deflexions, found for the α-particles from radium C' Hρ = 3∙983 × 10 5 E. M. U. and V = 1∙922 × 10 9 cm./sec., the accuracy being 1 in 400. In 1926 the writer measured Hρ for the same group of α-particles and found the value 3∙993 × 10 5 E. M. U. to 1 in 1000. This result, together with the value of the faraday and Aston’s determination of the atomic weight of helium, gave V = 1∙922 × 10 9 cm./sec. Absolute velocity determinations have been made for polonium by I. Curie, and for several groups by Rosenblum and Dupouy, who found for the radium C' group V = 1∙9218 × 10 9 cm./sec. with an accuracy greater than 1 in 1000. The velocities of over fifty α-particle groups have now been measured relative to the main radium C' group; these measurements have been summarized in a paper by Lewis and Bowden. The present paper describes a new determination of Hρ for this group. Using for E/M for the aparticle a value calculated from the faraday and the atomic weight of helium the velocity and energy have been calculated. The maximum error in Hρ is estimated to be of the order of 1 in 10 4 .