Résumé du preprint Irfu-09-163

Mesoporous silica films with varying porous volume fraction: direct correlation between ortho-positronium annihilation decay and escape yield into vacuum
L. Liszkay, C. Corbel, L. Raboin, J.-P. Boilot, P Perez, A. Brunet-Bruneau, P. Crivelli, U. Gendotti, A. Rubbia, T. Ohdaira, R. Suzuki
The behavior of ortho-positronium (o-Ps) in mesoporous silica films implanted with lowenergy 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.