Positron annihilation in Co2+-exchanged zeolite LTA

The positron life-time spectra of gradually dehydrated Co2+-exchanged zeolite LTA were analyzed with four life-time components. Whereas the first and third annihilation life-time components could be fixed to constant values, the second and fourth increased as water was gradually removed from the zeolite. After removing about 83% of the H2O molecules from the zeolite, when about 1.4 H2O molecules per Co2+ cation remained in the zeolite, marked variations were seen in the relative intensities of all four life-time components. At this point, the rate of positronium formation in the cavities of the zeolite decreased sharply. The pick-off life-time for the most dehydrated zeolite, τpick-off = 0.36 ns, estimated from the second life-time component, was used in the Tao–Eldrup model to estimate the cavity sizes in this zeolite. From the intensity ratio of the third to the fourth life-time components, 1.55, it is deduced that these components arise from the small and large cavities of the zeolite, respectively.