Positron lifetime measurements are made on γ‐irradiated poly(2,6‐dimethyl–1,4‐phenylene oxide) films as a function of the absorbed radiation dose in the radiation dosage range (0 to 24) × 10−5 Gy. All the measured lifetime spectra are well fitted to the three component analysis. Variations in the lifetimes and intensities of the first two components indicate that there is radiation induced molecular motions associated with the formation of free radicals. The average free volume size is calculated using the value of the o‐Ps lifetime at each irradiation step. The average free volume size varies from 0.134 to 0.162 nm3 over the absorbed radiation dose, while the number density of free volume sites is unaffected due to irradiation in the present dosage range.

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Positron annihilation studies were carried out on the Nasicon analogue Na2(La, AI)Zr(PO4)3 compound for three different concentrations (2-2, 2"8 and 5.2 by wt.%) of ZrO 2 in the nutrient. Angular correlation study of annihilated photons reveals that the defect concentration is maximum for 2.8 (wt.%) of ZrO 2. Further, positron lifetime studies indicate that the positrons are trapped at cation vacancies. Application of a twostate trapping model to this system made it possible to evaluate the lifetime of positrons in the Bloch state and of positrons trapped at cation vacancies. Keywortk. Nasicon analogue; positron annihilation spectroscopy; cation vacancies; trapping rate.

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