Positron Annihilation inCa2+-Doped KCl-Temperature and Magnetic Field Effects

The temperature dependence of the positron lifetime spectra shows, contrary to expectations based on earlier work, that all positive-ion vacancies introduced by ${\mathrm{Ca}}^{2+}$ doping can act as traps for positrons in which they annihilate with a distinct long lifetime. Magnetic quenching of the long-lifetime component indicates that in this state the positron wave function overlaps with a partially spin-polarized wave function of crystal electrons.