Abstract
Positron annihilatioin data collected for zeosil (a zeoilite-type solid allowing abundant Psformation) are discussed, with particular attention payed to the longest-lived positronium states as observed in lifetime spectroscopy experiments. To unravel the nature of these components, additional information was sought by applying an extermal magnetic field and by reecording the total energy distributioin of the annihilation 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 (140ns), therefore undergoing almost no pick-off annihilation. From the magnetic field experiments, the contact density parameter has a value of essentially 1, which is characteristic of an unpoerturbed triplet Ps state in vacuo. This positronium state therefore does not appear to interact with the medium.
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