Measurements of the relative velocities of the α-particles from radon, radium A, and radium C'

Abstract

In a previous paper the writer described measurements of the velocities of the main groups of α-particles from thorium X and its four α-radiating products, relative to the radium C' group which is commonly taken as a standard in such comparisons. The probable error in these measurements was estimated to be 1 in 20,000 to 1 in 30,000. Where comparable with the results published simultaneously by Rutherford, Wynn-Williams, Lewis, and Bowden, the agreement is very satisfactory, namely, 1 in 10,000 for thorium C (mean relative to radium C' and 1 in 30,000 for thorium C'. The present paper describes experiments in which the relative velocities of the radon, radium A, and radium C' groups have been measured, using apparatus of greater resolving power than in the experiments with thorium X; the probable error of the results is estimated to be of the order of 1 in 80,000. According to these experiments the velocities of the radon and radium A groups are somewhat higher than found in recent experiments by other observers. As in the experiments with thorium X the relative velocities were determined from the deflections recorded on a photographic plate using the earlier, or direct, magnetic deflection method. The source of α-particles was radon of high purity introduced directly from a purification plant into a small glass chamber which had a thin mica window and was situated within the vacuum exposure box. The correction for loss of velocity in the window was determined experimentally and the radon chamber was designed so that errors due to the recoil of the active deposit into the window or walls of the chamber would be eliminated.