Positronium binding energy

In contrast to the case for metals, positronium can be formed in the bulk of many insulators and molecular crystals, and any positronium which subsequently diffuses to the surface can be emitted into the vacuum with a kinetic energy < — Ps, where (f)Ps is the positronium work function. Its value can be expressed in terms of the binding energy of the positronium when in the solid, EB, and the positronium chemical potential, /xPs, as (Schultz and Lynn, 1988)... 

The scattering process can now be considered as a three-body problem, rather similar to positron scattering by atomic hydrogen but with the important difference that, because the ionization energy of an alkali atom is less than the binding energy of positronium, 6.8 eV, the positronium formation channel is open even at zero positron energy. 

Positronium formed in a positron-atom collision can be in a state with principal quantum number up to nPs provided that the kinetic energy of the incident positron, E, exceeds the difference between the ionization energy of the target, Ei, and the binding energy of the positronium in that state, i.e. 

Binding energies and annihilation rates for polyleptons are given in Table 2.2. The current values for positronium are listed for completeness. Since Wheeler s seminal 1946 paper, the 3- and 4-particle polyleptons have been the subject of many studies, and their properties are well understood today. The annihilation rate of diatomic positronium, Ps2, is about twice the spin-averaged rate in Eq. (2.4) because there are two positrons and each of them sees spin-paired electrons. Recently a calculation of the 5-particle... 

Coulombic attraction and increase average e+-e separation in the positronium. Both these factors decrease binding energy between the positron and electron constituting the positronium and therefore reduce the width of the Ore gap. 

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