Isotopic Effects in Single Filament Thermal Ion Sources

Isotopic effects occuring during the evaporation of microgram quantities of chemically pure rubidium, potassium and lithium compounds are studied. The measured isotopic ratios show a time dependent variation corresponding to a RAYLEIGH distillation. The fractionation factor is equal to the square root of the ratio of the masses. The highest observed enrichments are 45% for lithium, 10% for potassium and 5% for rubidium. The measured isotopic ratio depends also on the filament material and on the chemical composition of the sample. The discriminations are of the order of the square root of the ratio of the masses.