Investigation into the energy dependence of the annihilation cross-sections for Ne and Xe below the positronium formation threshold

Preliminary results into the energy dependence of the annihilation cross-section for Ne and Xe near and below the Ps formation threshold are presented. A non-negligible yield of ion-γ-ray coincidences has been observed significantly below the Ps formation threshold for Ne but not for Xe. This yield, which cannot at present be attributed to systematic effects, would imply an annihilation cross-section for Ne four orders of magnitude higher than predicted by theory. Further work is in progress