Positron Annihilation inCa2+-Doped KCl

A new third positron lifetime (∼ 1.3 nsec) component grows as the square root of the ${\mathrm{Ca}}^{2+}$ concentration. It is attributed to the diffusion of positrons (diffusion constant $D_{+}\left(\mathrm{KCl}\right)\simeq 6\times {10}^{-3\mathrm{}}$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$) until annihilation at free-cation vacancies introduced by ${\mathrm{Ca}}^{2+}$ doping.