Masses of some Light Atoms measured by means of a New Mass-Spectrograph

Abstract

SINCE nay last letter on this subject¹, I have designed and constructed my third mass-spectrograph which embodies second-order focusing. The dispersion, from 4 mm. to 6 mm. for one per cent difference of mass, was calibrated by means of the twin lines of bromine, which were found to have a difference of 1.9983 ± 0.0015 units. The D, H₂ doublet can now be obtained perfectly resolved, and as the lines are not seriously curved it is not difficult to estimate their separation to 0.005 mm. so that an accuracy of 1 in 10⁵ is theoretically possible. Unfortunately, the differences in mass deduced from individual doublets show variations greater than this. These appear to depend on the condition of the discharge and are probably due to the uneven illumination of the front slit causing lateral structure in the lines themselves, which may not be quite the same for particles so different as an atom and a molecule. It is hoped to get rid of this technical difficulty as the work proceeds.