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 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 external magnetic field and by recording the total energy distribution 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 (140 ns), 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 unperturbed triplet Ps state in vacuo. This positronium state therefore does not appear to interact with the medium.