Temperature dependence of positron diffusion in metals

Data are presented for the positron diffusion coefficient, D₊, in single crystals of Mo, Nb, Al, and Cd. The data clearly demonstrate that the temperature dependence of D₊ is much stronger than the T^-0.5 that is theoretically predicted, ranging from about T^-0.8 to a maximum of T^-2.6. In addition, our results shown an anisotropy for the temperature dependences of D₊ in two principal directions of Cd (T^-1.0 along an a axis versus T^-2.6 along the c axis) which cannot be described by a simple diffusion model.