Aggregation ofPb2+Impurities in NaCl and KCl

The aggregation of ${\mathrm{Pb}}^{2+}$ impurity-vacancy complexes has been studied by measurement of dielectric loss and ionic thermocurrents (ITC) in KCl and NaCl and by the decay of luminescence in NaCl. A third-order reaction has been observed to govern the loss of complexes in crystals with high Pb content (above 100 ppm), while for dilute crystals (under 20 ppm) the reaction order is neither second nor third. The decay of luminescence in dilute NaCl was also neither second nor third order but was faster than the ITC decay.