Basing on the approach to the calculations of the positron trapping ra
te presented by Shirai and Takamura [1], an attempt is made to explain
the prevacancy effects observed in positron annihilation measurements
in real metals. The calculations are done for the point defect and fo
r the dislocation, taking into account the thermal distribution of the
positron energy and the thermal expansion of the crystal lattice. In
spite of the thermal distribution of energy of thermalized positrons t
he resonance trapping of positrons can be responsible for prevacancy e
ffects in metals and can help solve some problems in the study of posi
tron annihilation.