[en] In a rotating neon plasma, centrifuging should produce separation of Ne20 and Ne22 isotopes. Isotope separation was measured by extracting a sample of gas from the plasma region, and analysing it using a mass spectrometer. The sample is extracted using a fast-acting gas valve which opens for 150 μsec. This allows time-resolution during the life of the plasma, which is of several milliseconds duration. The dependence of isotope separation on various parameters was investigated and changes in isotopic ratio of 20 per cent were observed. Results are compared with a simple equilibrium model based on observed electrical probe voltages and spectroscopic temperature measurements. As well as centrifugal separation, diffusive separation occurs in gas flow through the fast-acting valve, producing a small change in neon isotopic ratio. This effect is allowed for in isotope separation predictions. (author)