The ratio of the total molar rate of flow through the barrier within a converter to the total rate of flow into the same converter is called the cut and is designated by the Greek letter .

hi a production cascade, a cut of approximately 0.5 is the optimum value with respect to operating efficiency and production.

Figure A-1 "R" Stage Separation

The actual separation achieved by a stage is expressed in terms of the mol fraction of the light component and for the purpose of this discussion is designated by the capital letter R. It can be defined as follows: if Y is the concentration of light component in the enriched stream leaving a converter and X is its concentration in the depleted stream leaving the same converter, then

This definition is similar to that of the separation factor, but, as shown in Figure A-1, the value of R is based on the overall separation of a stage while that of the separation factor is based on the performance of the barrier alone. The relation between the two is given by the following equation.

E is a correction factor called the mixing efficiency. It can be explained as follows: since the light component passes through the barrier more rapidly than the heavy component, the layer of gas at the surface on the high pressure side of the barrier becomes more depleted in the light component than the bulk of the gas on the high pressure side. Thus, there is a concentration gradient perpendicular to the surface of the barrier which results in a decrease in separation. In the particular process of separation of uranium isotopes, the value of R in the preceding equation differs very little from unity (R =1.003) and is somewhat inconvenient for use in calculations. By subtracting 1 from each side of the equation, equating the symbol (psi) to R - 1, and by making a slight approximation, the equation becomes

This equation is used frequently in the plant in making separation tests.