Isotope Separation of Argon by Axial Flow Turbo-Machine, (I)

Abstract

The strong dependence on molecular weight shown by the compression ratio of a turbo-molecular pump for high vacuum suggests its possible utility for isotope separation. The separation factor obtainable with a multistage turbo-machine was estimated by means of a simplified calculation assuming molecular flow, and zero net throughput. The separation factor depends on the rotating speed of the pump, and attains maximum value when the speed of the blades is close to the most probable speed of the molecules. To study this effect experimentally, the separation factors were measured on Ar isotopes as a function of pressure and speed of rotation, using a turbo-molecular pump for high vacuum. The Ar gas was fed into the higher pressure side of the pump, to flow against the impeller action through the pump stages, and emerge on the lower- pressure side with its light component enriched. The abundance ratio between 36Ar and 40Ar was measured to determine the separation factor. The measured values of separation factor were 1.40, 1.65, 1.80 and 1.95 at 4,500, 6,000, 9,000 and 12,000 r.p.m., respectively, which were fairly close to the calculated data at low working pressures, but fell appreciably short of prediction as the pressure increased.