Positron interactions in solids
Characterization of lacunar defects by positron annihilation

When an energetic positron penetrates a solid, it rapidly loses its energy through ionization and electron excitations, before finally thermalizing and exciting the solid's vibration modes. The calculated times for this slowing-down and stopping phase are very short, of the order of a few 10 ^-12 s [36] . During this phase, the probability of annihilation with electrons is much lower than the probability of inelastic or elastic scattering. The probability of annihilation becomes significant as the thermalized positrons diffuse into the solid.