Effect of colour centres ( F '-centres) on the depolarization of positive mouns in KCl

First results are reported of a project to study the depolarization- and diffusion mechanisms of positive muons in ionic crystals by observing the effect that the presence of charged defect centres has on the residualμ+-polarization. It is shown that theμ+-polarization in KCl is significantly increased by the presence ofF′-centres. The muons “find” theF′-centres at concentrations of a few ppm at temperatures as low as 10 K.