MAGNETIC QUENCHING EFFECTS ON LONG-LIVED POSITRONIUM STATES IN ZEOSIL

Positron annihilation data collected for zeosil (a zeolite-type solid allowing abundant Ps formation) are discussed, with particular attenti on payed to the longest-lived positronium states as observed in lifeti me spectroscopy experiments. To unravel the nature of these components , additional information was sought by applying an external magnetic f ield and by recording the total energy distribution of the annihilatio n radiation. From both the lifetime and the extended Doppler spectra, it is shown that positronium presents a very long-lived component with a relative intensity of ca. 30% and a lifetime close to the intrinsic tripler lifetime (140 ns), therefore undergoing almost no pick-off an nihilation. From the magnetic field experiments, the contact density p arameter has a value of essentially 1, which is characteristic of an u nperturbed triplet Ps state in vacuo. This positronium state therefore does not appear to interact with the medium.