Positron annihilation Doppler broadening study of niobium

Doppler broadening of the positron annihilation lineshape has been measured for 99.995 wt % pure niobium in the temperature range 300 to 2581/sup 0/K. It was found that the effect of the equilibrium vacancies upon the Doppler-broadened lineshape in pure niobium is much smaller than that normally found for other metals, in agreement with an earlier study. Furthermore, the addition of 100 at. ppM oxygen to the niobium produced no measurable effects on the lineshape, within the experimental uncertainties, either within or below the vacancy-sensitive temperature region. The results are discussed in relation to previous investigations of positron trapping at vacancies in niobium, as well as to studies of vacancy migration in metals.