Testing ETE model, temperature dependences of PALS data

Three porous glasses produced by sol-gel method were investigated using Positron annihilation lifetime spectroscopy (PALS) method. The theoretical curves calculated from the pick-off annihilation model for cylindrical and spherical free volumes were compared to the results of PALS measurements done in the temperature range from 100 to 500 K. The o-Ps mean lifetime values in the pores found in the experiment change with temperature in the glasses containing pores of R < 1.5 nm in the range up to 40 ns, while the model predicts these changes less then 10 ns. The meaningful discrepancy between experimental data and model predictions was found at low temperatures. The discrepancy diminishes with increasing pore sizes. In the glass containing the largest pores, R- 2 nm, experimental values of o-Ps lifetime agree well with model predictions.