Positron diffusion in solids and in liquid metals

The paper gives a brief review of the theory of the positron diffusivity, D+, in condensed matter with emphasis on the role of “e+-polarons” (Section 1), on hexagonal metals (Section 2), and on the interaction of positrons and positronium with optical phonons, including the thermalization of positronium (Section 3). For D+ in liquid metals two possible scenarios are predicted (Section 4): Either small effective positron mass m+ and high positron diffusivity with T12 temperature dependence, or large m+ and low D+, exhibiting a stronger, Arrhenius-type temperature dependence. Recent slow-positron work indicates that the first scenario is realized in liquid Bi and the second one in liquid Ga.