A QUANTITATIVE STUDY OF SCATTERING PHENOMENA IN AN ELECTROMAGNETIC SEPARATOR

Abstract

A series of recent experiments has shown that the elastic scattering of a directed ion beam by residual gas is one of the dominant factors causing contamination in an electromagnetic mass separator. This phenomenon is treated numerically, based on geometrical considerations and on an appropriate and reliable interaction potential between the ions and the residual gas molecules. The result is a relation[Formula: see text]expressing the fractional contamination as a function of: the residual gas molecule concentration n_r, the fractional mass difference ΔM/M, the collector slit width Δx, the configuration factor [Formula: see text] and constants (σ₀ and n) which appear in the expression for the differential cross section. The reciprocal value [Formula: see text] imposes an upper limit to the enhancement factor. By performing the various integrations in a different sequence, a general expression for the transmission from source to collector is obtained. The influence of losses caused by inelastic scattering can be easily incorporated. For elements with a mass number of about 200, scattered by air and for an accelerating voltage of about 30 kv, this expression takes the form:[Formula: see text]where L is the total ion path length in the separator.