Pick-off quenching probability of ortho-positronium per collision with atoms and molecules K. Wada, F. Saito, N. Shinohara and T. Hyodo Eur. Phys. J. D, 66 4 (2012) 108 Published online: 30 April 2012 DOI: 10.1140/epjd/e2012-20668-5