An a.c. Operated Mass Spectrometer for Isotope Abundance Measurements

A mass spectrometer of the Nier type has been designed and constructed for the identification of isotopes and measurement of their relative abundances. This instrument employs a universal gas-type ion source which may readily be replaced with a furnace or filament-type ion source for use with solids. The instrument is compact and portable with the exception of service connexions and a galvanometer shelf. The electronic units designed for this instrument are described in detail. These units operate satisfactorily from unstabilized a.c. and do not require batteries. The mass spectrometer is capable of detecting isotopic components present to the extent of 1 part in 100,000 of a sample. With the present slit dimensions, the instrument was found to have a resolving power better than 1 in 130, which agrees with that calculated from the slit dimensions and the radius of curvature.