Detecting Positron-Atom Bound States through Resonant Annihilation

A method is proposed for detecting positron-atom bound states by observing enhanced positron annihilation due to electronic Feshbach resonances at electron-volt energies. The method is applicable to a range of open-shell transition-metal atoms which are likely to bind the positron: Fe, Co, Ni, Tc, Ru, Rh, Sn, Sb, Ta, W, Os, Ir, and Pt. Estimates of their binding energies are provided.

Figure 1

Dipole polarizabilities ${\alpha }_d$ (from Ref. 25, except for Au [33]) vs ionization potentials for atoms in the range where positron binding can be expected. Solid squares show atoms for which positron binding is predicted by high-quality calculations. The horizontal line ${\alpha }_d=40\mathrm{a}.\mathrm{u}.$ is an approximate boundary between binding and nonbinding atoms.