Tritium diffusion in V, Nb and Ta

Abstract

Gorsky-effect measurements of the diffusion coefficient of tritium (T) in V, Nb and Ta are reported. The measurements were performed at small T concentrations (less than about 1.4 at.%), and in the temperature range from -140 degrees C to 100 degrees C. Comparison with results obtained for H and D shows an increase of the activation energy with increasing isotopic mass. For Nb and Ta, the pre-exponential factors are identical for all the isotopes, whereas for V this factor is appreciably larger for T and for H and D. The reduction of the relaxation strength in the presence of precipitation allows a rough determination of the solubility limit, which is found to be isotope independent for Nb and Ta. In V, the solubility limit for T is shifted slightly to lower temperatures. The H, D or T induced lattice expansion calculated from the relaxation strength shows no dependence on isotopic mass.