Application of pulsed slow positron beams using a radioactive element to polymers

A positron-annihilation lifetime technique was applied to study surface properties of polymers. The instrument for this experiment, which generated pulsed slow positron beams, was developed by using 22Na radioisotope. The size and distribution of intermolecular-space holes was found to be constant, independent of the penetration depth of injected-positron beams in the energy between 1.2 and 10.2 keV. The characteristic lifetime in Teflon, 4ns, was observed in the sample of Fe(50 nm) evaporated on Teflon substrate for injected positrons with energy above 2.5 keV, and the boundary between Fe and Teflon substrate could be detected. Positron lifetime for polymers was measured along the direction of pulsed slow positron beams, and diffusion length of positronium was obtained from the measurement of the intensity. (Y. Kazumata)