4. Determining the free volume of defects in the core or surface of materials

This paragraph illustrates the properties of lacunar defects that positrons have made it possible to determine in metals, semiconductors or insulators, based on the following annihilation characteristics:

• living time

${\text{τ}}_{\text{d}}$

• moment distribution of annihilated electron-positron pairs ${\rho }_d$ (p) ;

• annihilation fraction of low-momentum electron-positron pairs S _d ;

• annihilation...