Element-specific momentum distributions of positron and positronium annihilation in polymers

Intrinsic momentum distributions of positrons, para-positronium (p-Ps), and ortho-positronium (o-Ps) in polymers derived from the correlation between the S parameter and the o-Ps fraction are discussed. They have strong element-specificity among carbon- (C-group), oxygen- (O-group), and fluorine-containing polymer groups (F-group). The momentum distributions of positrons are narrower in the order of C-, O-, and F-groups. They unexpectedly extend beyond 30×10-3m0c and cannot be approximated by either a single or the sum of Gaussian, implying that different electron states contribute to the momentum distributions. The p-Ps profile in the F-group is 1.4 times as broad as those of the C- and O-groups, whereas o-Ps profiles are essentially identical in the three polymer groups.