Positron Annihilation Centers in NaCl

The intensity of the long-lived component in the positron lifetime spectrum of NaCl is found to be correlated with the x-ray-induced growth and thermal annealing of the $V$-region color centers. If this lifetime component is attributed to positrons annihilating on defects, called annihilation or $A$ centers, the data indicate that $V$-center formation reduces $A$-center formation. The results suggest that positron-annihilation measurements can serve as an important complement to color-center measurements in the study of defects in ionic crystals.