Fig. 6.

Left Scheme of the ortho-positronium annihilation into three gamma quanta ${\mathit{\gamma }}_i$ in the detector reference frame. Gamma quanta are not contained in a single plane due to non-zero kinetic energy of the ortho-positronium. In the experiment a plane of response can be determined from gamma quanta interaction position in the scintillators (green bars). The distance d between plane of response and annihilation vertex gives information about annihilation position uncertainty. Right Distribution of distance d as a function of kinetic energy of ortho-positronium. Taking into account resolution of the J-PET annihilation point reconstruction [18], the uncertainty caused by o-Ps’s boost is negligible