Thermal expansion effects in positron lifetimes

The precision of relative positron lifetime measurements is now sufficient to observe directly changes due to lattice thermal expansion. This information is necessary for the determination of accurate vacancy formation energies from positron annihilation data obtained over a higher temperature range. Measurements have been made of the change in positron lifetime in the metals Au, Ag, Cu, and Al over the temperature range 100–300 K where there is no contribution from positron trapping at vacancies. The results are compared with theoretical calculations which take account of positron annihilations with both valence and core electrons.