Observation of Spin-Conversion of Positronium in Zeolite

We have measured the positron lifetime spectra of zeolite 13X as a function of exposed air pressure. Four lifetime components have been obtained and properly assigned. The longer lifetimes τ₃ and τ₄, are attributed to ortho-positronium annihilating in the β-cage and supercage in zeolite respectively. More interesting observation is that the positron annihilation parameters vary significantly with the exposed air pressure. It is interpreted in terms of the spin-conversion of positronium with paramagnetic oxygen.