Positron and positronium binding to atoms

Abstract

Recent research has shown that there are a number of atoms and atomic ions that can bind a positron. The number of atoms known to be capable of binding a positron has expanded enormously in recent years, with Li, He(3 S e), Be, Na, Mg, Ca, Cu, Zn, Sr, Ag and Cd all capable of binding a positron. The structure of these systems is largely determined by the competition between the positron and the nucleus to bind the loosely bound valence electrons. Some systems, such as e + Li and e + Na, can be best described as a Ps cluster orbiting a charged Li + or Na + core, while others such as e + Be consist of a positron orbiting a polarized Be atom. In addition, a number of atoms (Li, C, O, F, Na, Cl, K, Cl, Cu, Br) can bind positronium and a few systems capable of binding two positrons have also been identified. These positron-binding systems decay by electron-positron annihilation with the annihilation rate for e + A systems largely determined by the parent atom ionization potential.

Stability of few-charge systems in quantum mechanics

“…[156, p. 263]. What is of interest to us is the fact that, if annihilation is neglected, there are many examples of stable configurations where a positron is attached to an atom or an ion [3].…”

Positron scattering and annihilation from hydrogenlike ions

“…This effect will be called the clustering effect and is well known in condensed-matter systems [33,34], positron-atom scattering systems [20,29,30,36], and positron-atom bound states [19,37].…”

Formation of positron-atom bound states in collisions between Rydberg Ps and neutral atoms

“…The form of the positron wave function used in the derivation is correct for binding by atoms or molecules with ionization potentials I > 6.8 eV. For atoms with I < 6.8 eV, the asymptotic wave function corresponds to Ps(1s) bound to the positive ion, and the dominant form of the bound-state wavefunction is the 'Ps-ion cluster' [12]. However, it still contains a 'positron-atom component,' and the present cross sections could be used with caution as order-of-magnitude estimates.…”

“…Detection of positron-atom bound states in reaction (2) will be the first observation of its kind. A comparison of the measured cross section with the theoretical results derived in this paper should provide an estimate of the positron binding energy, which could be compared with existing high-quality predictions [12][13][14]. It would also be interesting to apply this method to molecules for which the binding energies are known from the resonant annihilation studies [15,[19][20][21][22].…”

“…Soon after, many calculations of positron binding to other atoms appeared; see Ref. [12] for a 2002 review. Despite a wealth of predictions for positron-atom binding energies now available (for a survey of the Periodic Table, see Refs.…”