Determination of the $3\gamma$ fraction from positron annihilation in mesoporous materials for symmetry violation experiment with J-PET scanner

Various mesoporous materials were investigated to choose the best material for experiments requiring high yield of long-lived positronium. We found that the fraction of $3\gamma$ annihilation determined using $\gamma$-ray energy spectra and positron annihilation lifetime spectra (PAL) changed from 20% to 25%. The $3\gamma$ fraction and o-Ps formation probability in the polymer XAD-4 is found to be the largest. Elemental analysis performed using scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscope EDS shows high purity of the investigated materials.