Investigations of Positronium Formation and Destruction Using $3\ensuremath{\gamma}/2\ensuremath{\gamma}$Annihilation-Ratio Measurements

Investigations of Positronium Formation and Destruction Using $3 γ / 2 γ$ Annihilation-Ratio Measurements

W. E. Kauppila, E. G. Miller, H. F. M. Mohamed, K. Pipinos, T. S. Stein, and E. Surdutovich

Phys. Rev. Lett. 93, 113401 – Published 9 September 2004

Abstract

Positronium (Ps) produced by 4 to 40 eV positrons colliding with Ne, Ar, Kr, ${C O}_{2}$ , and $O_{2}$ is investigated by measuring the ratio of signals of two gamma rays in coincidence resulting from (a) three gamma annihilation of ortho-Ps and (b) two annihilation gamma rays due to para-Ps decay and destruction of ortho-Ps at an aluminum scattering cell surface. These ratios provide evidence that relates to the kinetic energy dependence of ortho-Ps interactions with an aluminum surface, the Ps formation potential at this surface, and the fact that Ps is being formed with inner orbital electrons for ${C O}_{2}$ and $O_{2}$ .