POSITRON IRRADIATION EFFECTS DURING POSITRON-ANNIHILATION LIFETIME MEASUREMENT IN POLYMERS

The time-dependent variation in ortho-positronium (o-Ps) intensity I-3 has been investigated during long-term positron lifetime measurements in polymers. It has been found that I-3 in polar polymers, e.g. poly( ether methane), almost keeps constant, while in nonpolar polymers, hig h-density polyethylene and polypropylene, I-3 decreases as a function of positron source exposure time. The formation of Ps-inhibiting; spec ies induced by the positron source radiation might give rise to the de crease of the o-Ps intensity I-3.