Effect of positron irradiation was studied using both positron lifetime and Doppler.
Positron source irradiation creates paramagnetic centers on the surface of alumina.
Paramagnetic centers induced spin conversion quenching of positronium.
Paramagnetic centers are unstable above 70 K and nearly vanish above 190 K.
Positronium is a sensitive probe for the surface defects in porous materials.