Measurement of U diffusion in Nb using alpha-Spectrometry

U bulk diffusion in Nb was measured by mean α-spectrometry in the temperature range 1533 to 1673 K (1260 to 1400°C). Measurements obey the Arrhenius law with diffusion parameters Q = 423 ± 10 KJ/mol and D₀ = (2.5 ± 1)×10⁻⁴ m²/s very close to the Nb self-diffusion ones found in the literature. This behaviour is compatible with the hypothesis that U diffuses in the Nb lattice via a vacancy mechanism, at the same time it is in disagreement with previous measurements of U diffusion performed at higher temperatures, where the activation energy is significant lower.