Positron Annihilation in Synthetic Zeolites 4A and 13X

We have measured the rates of positron annihilation in synthetic zeolites 4A and 13X under a variety of conditions. For zeolites 4A and 13X, respectively, long lifetime values (τ2 in nanoseconds) and intensities I2 (listed in parentheses) were found as follows: hydrated, 2.26 ± 0.18(20.5%) and 1.95 ± 0.20(21.6%); evacuated, 3.76 ± 0.10(25.4%) and 4.42 ± 0.25(21.8%); filled with O2, 3.34 ± 0.25(4.2%) and 4.15 ± 0.35(4.6%); filled with He, 2.90 ± 0.11(23.8)% and 3.28 ± 0.12(20.0%); filled with N2, 2.97 ± 0.12(23.7%) and 3.39 ± 0.10(25.3%); filled with methane, 4.10 ± 0.06(28.2%) and 3.78 ± 0.11(24.8%). Very long components (τ3) with lifetimes of 42.2 ± 11.2 nsec and 41.4 ± 4.0 nsec for 4A and 13X, respectively, were observed in evacuated zeolites. Because the cavity sizes are well known from x‐ray diffraction studies, the slightly larger lifetime observed in 13X relative to 4A for evacuated zeolites is thought to reflect the larger free volume present in the 13X configuration. The reduced lifetimes observed...