A technique for studying paramagnetic defects in insulators or semicon
ductors acting as positron traps is presented. The spin polarization o
f the paramagnetic electrons of such centres can be determined by inve
stigating the annihilation of spin-polarized positrons, e.g. by Dopple
r broadening (DB) or positron lifetime measurements. The viability of
this technique is demonstrated by measuring the temperature dependence
of the polarization of the paramagnetic electrons in F-centres in KCl
in high magnetic fields (+/-4.5T).