We report experimental evidence that the rate nu at which a negative ion nucleates vortex rings in He II is strongly influenced by 3He isotopic impurity concentrations close to that of the natural abundance. We suggest that the anomalous temperature dependence of nu observed near 0.3K in earlier experiments in natural 4He is a consequence of 3He condensation on the ions, and we deduce from our data that the presence of as few as five condensed atoms is sufficient to completely eliminate the bare ion signal in a typical experimental geometry.