Isotope analysis

The difference in concentration of a selected isotope in two materials is measured by directing gaseous beams of the materials towards the inlet of a mass spectrometer. A shutter alternately blocks transmission of the two beams. Means is also provided for blocking either of the two beams for any period of time desired. Provision is made for automatically passing either one of the gaseous beams or both of the gaseous beams through the shutter to the mass spectrometer. The output signal from the mass spectrometer is passed to a synchronous detector as is a reference signal which is representative of the speed of operation of the shutter. The output signal from the synchronous detector is representative of the concentration of the selected isotope in a first material if only the gaseous beam of the first material is being passed through the shutter to the mass spectrometer. The output signal from the synchronous detector is representative of the concentration of the selected isotope in the second material if only the gaseous beam of the second material is being passed through the shutter to the mass spectrometer. The output signal from the synchronous detector is representative of the difference in concentration of a selected isotope in the two materials if both of the gaseous beams are being passed through the shutter alternately to the mass spectrometer. If desired, these outputs may be utilized to calculate the isotope ratio difference ( Delta ) for the selected isotope in the two materials