Nb diffusion in single-crystal alpha-Zr

Measurements of Nb-93,Nb-94 diffusion in alpha-Zr single crystals have been made in the range 1000-1100 K. The specimens had very low Fe contents (< 1.0 ppma). Diffusion coefficients (D) were measured in directions which were either parallel (D-parallel to) or perpendicular (D-perpendicular to) to the c-axis. Sectioning was done with a microtome and both liquid scintillation and gamma ray assay were applied to determine the Nb activity and diffusion profiles. In some experiments D-parallel to and D-perpendicular to were measured on the same (two-faced) specimen; D(T) is characterised by: D = 1.88x10(-4) exp(-2.69 eV/kT) m(2)/s, with D-perpendicular to being marginally larger than D-parallel to. Further Nb diffusivities, measured by sputter-sectioning (both directly and as a by-product of Zr-95 self-diffusion measurements), are in reasonable accord with the microtome data.