Positronium formation in positron-helium collisions

Fig. 4.11. The angular distribution of positronium formation in positron-helium collisions at various energies in the Ore gap (Van Reeth and Humberston (1999b). The results for E = 17.8 eV, just above the positronium formation threshold, have been multiplied by a factor of 30.

The most accurate theoretical results for positronium formation in positron-helium collisions in the energy range 20-150 eV are probably those of Campbell et al. (1998a), who used the coupled-state method with the lowest three positronium states and 24 helium states, each of which was represented by an uncorrelated frozen orbital wave function... 

Igarashi, A. and Toshima, N. (1992). Positronium formation in positron-helium collisions at intermediate energies. Phys. Lett. A 164 70-72. 

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