Isotope analysis

The difference in concentration of a selected isotope in two materials is measured by directing gaseous beams of the materials toward the inlet of a mass spectrometer. A shutter alternately blocks transmission of the two beams. An output signal from the mass spectrometer, which is representative of a selected isotope, is passed to a synchronous detector, as is a reference signal which is representative of the speed of operation of the shutter. 6 Claims, 3 Drawing Figures