POSITRONIUM FORMATION IN SEMICRYSTALLINE POLY(ETHYLENE-TEREPHTHALATE)

The probability of positronium (Ps) formation in semicrystalline poly( ethylene terephthalate) (PET), has been investigated by means of posit ron annihilation lifetime spectroscopy (p.a.l.s.). The p.a.l.s. data a re correlated with the structural characteristics of the samples, such as crystalline content, interlamellar spacing and lamella thickness. The results show an approximately linear decrease of the intensity (I- 3) of the long-lived orthopositronium (o-Ps) component with an increas e in the crystalline content up to 53%, while the lifetime remains pra ctically constant. It seems that the other structural parameters do no t affect the Ps formation. The decrease of I-3 cannot be completely ac counted for if one assumes that o-Ps localizes in the amorphous phase only. It is suggested that the o-Ps also forms in the crystalline regi ons, due to the inhomogeneous electron density distribution along the c-axis of the PET lattice.