Positronium formation cross-sections for Xe, CO2 and N2

The positronium formation cross-sections for Xe, CO2 and N-2 have been measured using coincidences between gamma-rays from positronium self-annihilation and the resultant ion. In the case of Xe, there is excellent agreement with previous experimental determinations. For CO2 there is broad agreement in magnitude with previous measurements in contrast with N-2 where good shape agreement at low energies (<40 eV) is found though the magnitude of the present cross-section is significantly higher.