Temperature dependence of condensed methane studied by positron lifetime measurements

Positron lifetime spectra have been measured as a function of temperature from 30 K to 150 K in condensed methane. In solid phase, the positronium (Ps) formation in free volume and the Ps yield of 27% were observed. The sigmoidal variation of o-Ps lifetime with temperature was interpreted by Ps trapping in the thermally activated defects. The activated energy Ea = 0.10 ± 0.02 eV was derived in terms of Ps trapping model. In liquid methane with saturated vapor pressure, the results that o-Ps lifetime is 5-7 ns and Ps formation probability is 36% indicate the Ps bubble formation. The temperature dependence of the bubble size and surface tension were estimated