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International audienceThe behavior of ortho-positronium (o-Ps) in mesoporous silica films implanted with low-energy positrons has been studied as a function of the film porous volume fraction. A lifetime spectrometer allowed determination of o-Ps annihilation decay both inside and outside of the film. A kinetic model is introduced that permits the determination of the yield and rate of escape of o-Ps into vacuum as well as the annihilation decay rate of the trapped o-Ps in the film. It is shown that these undergo a sudden change at a threshold porous volume fraction, above which the o-Ps escape rate to vacuum varies linearly with volume fraction. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3234381

applied physics letters

Mesoporous silica films with varying porous volume fraction: Direct correlation between ortho-positronium annihilation decay and escape yield into vacuum