FORMATION OF POSITRONIUM IN CONDENSED MATTER STUDIED BY MEANS OF DOPPLER BROADENING EXPERIMENTS WITH SPIN-POLARIZED POSITRONS

By means of the so-called e(+)SR (positron spin relaxation) technique, spin-polarized positrons from radioactive sources emitting relativist ic e(+) permit to investigate the formation and the properties of posi tronium (Ps) in condensed matter. This is demonstrated on teflon and c rystalline quartz in a facility utilizing a Ge-68/Ga-68 source and mea suring the effect of the reversal of a longitudinal (with respect to t he e(+) spin polarization) magnetic field on the Doppler broadening of the 511 keV annihilation photon line. A novel data-analysis procedure allows the full information contained in the Doppler-broadened spectr a to be extracted and the Ps-forming e(+) fractions and the overlap of the e(+) and e(-) wavefunctions in Ps to be deduced.