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, high-density polyethylene and polypropylene, I-3 decreases as a function of positron source exposure time. The formation of Ps-inhibiting; species induced by the positron source radiation might give rise to the decrease of the o-Ps intensity I-3.