THE OBSERVATION ON o-Ps ANNIHILATION IN SILICA AEROGEL BY COMBINED SPECTROMETER

The yields and energy spectra of the various components of o-P_s annihilation in silica aerogel are observed using the combined spectrometer. It is shown that the processes of P_s formation and annihilation in ultrafine grains of SiO₂ aerogel are basically consistent with the diffusion model, but the grain surface effect can not be neglected. Comparing the Dopplar broadening spectra, it is understood that the pick-off process of the longest component possesses the lower annihilation momentum than that of the free positron annihilation.