  We present an analysis of positron lifetimes in solids with unprecedented
depth. Instead of modeling correlation effects with density functionals, we
study positron-electron wave functions with long-range correlations included.
This gives new insight in understanding positron annihilation in metals,
insulators and semiconductors. By using a new quantum Monte Carlo approach for
computation of positron lifetimes, an improved accuracy compared to previous
computations is obtained for a representative set of materials when compared
with experiment. Thus we present a method without free parameters as a useful
alternative to the already existing methods for modeling positrons in solids.
