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 3gamma fraction and o-Ps formation probability in the polymer XAD-4 is found to be the largest. Elemental analysis performed using scanning electron microscop (SEM) equipped with energy-dispersive X-ray spectroscop EDS show high purity of the investigated materials. 
B. Jasi\'nska, M. Gorgol, M. Wiertel, R. Zaleski, D. Alfs, T.   Bednarski, P. Bia{\l}as, E. Czerwi\'nski, K. Dulski, A. Gajo...
nucl-ex physics.ins-det