The Isotope Effect for Electromigration of Sodium Ions in Molten Sodium Nitrate

2 2 Na and the stable isotope 2 3 Na. The accuracy of that experiment was, however, low, because the specif ic activity measurement was based on the assumption that the sodium nitrate was pure, while a certain contamination due to thermal decomposition, corros ion of the packing material, etc. could hardly be avoided. The purpose of the present work is to re-determine the mass effect by using two radioactive isotopes 2 2 Na and 2 4 Na which should enable a higher accuracy, with the ob ject of comparing with the results obtained by zone e lectromigrat ion 4 and, at the same time, to conf i rm the basic assumption that there is no dif ference whether the mass effect is determined f o r a tracer isotope ( 2 2 Na) and a dominating isotope ( 2 3 N a ) , or f o r two tracer isotopes ( 2 2 N a and 2 4 N a ) . Another aim of this work is to measure the temperature dependence of the mass effect.