A New Mass Spectrometer

A new type of mass spectrometer has been constructed in which no magnetic fields are used. By applying an alternating electric field at right angles to the beam of positive particles all but certain velocities are removed from the beam. Because of the fact that a symmetry not contemplated in the theory previously published was introduced in the construction for mechanical reasons, the apparatus transmits some other velocities besides those desired. This produces extra peaks and complicates the mass spectrum. Because of this and the fact that the apparatus is badly contaminated with mercury from the diffusion pumps in spite of the continued use of liquid air, we have designed a new apparatus in which, it is expected, both effects will be eliminated. Comparison of the peak at 32 with that at 34 gives a maximum ratio of the intensity of ${\mathrm{O}}_{16}$ ${\mathrm{O}}_{16}$ to ${\mathrm{O}}_{16}$ ${\mathrm{O}}_{18}$+${\mathrm{Hg}}_{204}^{6+}$ of 300. This is presumably the ratio with the smallest contamination of mercury and means that the ratio of ${\mathrm{O}}_{16}$ to ${\mathrm{O}}_{18}$ is greater than 600.