Configuration-interaction calculations of positron binding to zinc and cadmium

Abstract

The configuration-interaction method is applied to the study of positronic zinc ${(e}^{+}\mathrm{Zn})$ and positronic cadmium ${(e}^{+}\mathrm{Cd}).$ The estimated binding energies and annihilation rates were 0.003 73 hartree and $0.42\ifmmode\times\else\texttimes\fi{}{10}^{9} {\mathrm{sec}}^{\ensuremath{-}1}$ for ${e}^{+}\mathrm{Zn}$ and 0.006 10 hartree and $0.56\ifmmode\times\else\texttimes\fi{}{10}^{9} {\mathrm{sec}}^{\ensuremath{-}1}$ for ${e}^{+}\mathrm{Cd}.$ The low-energy elastic cross section and ${Z}_{\mathrm{eff}}$ were estimated from a model potential that was tuned to the binding energies and annihilation rates. Since the scattering lengths were positive ${(14.5a}_{0}$ for Zn and ${11.6a}_{0}$ for Cd) the differential cross sections are larger at backward angles than at forward angles just above threshold. The possibilities of measuring differential cross sections to confirm positron binding to these atoms is discussed.