Electron-positron momentum distribution in cadmium: evidence for self-trapped positrons below the vacancy trapping region

Equilibrium measurements of the temperature dependence of the peak coincidence rate from positrons annihilating in Cd show that there are two regions of linear slope at temperatures below the vacancy trapping region. The electron-positron momentum distribution measured in the region of intermediate slope exhibits smearing consistent with positron localization in a self-trapped state. In this state a decrease of 8% in the core annihilation rate is also observed.