Configuration-interaction calculations of positron binding to zinc and cadmium

The configuration-interaction method is applied to the study of positronic zinc (e⁺Zn) and positronic cadmium (e⁺Cd). The estimated binding energies and annihilation rates were 0.003 73 hartree and 0.42×10⁹ sec^-1 for e⁺Zn and 0.006 10 hartree and 0.56×10⁹ sec^-1 for e⁺Cd. The low-energy elastic cross section and Z_eff were estimated from a model potential that was tuned to the binding energies and annihilation rates. Since the scattering lengths were positive (14.5a₀ for Zn and 11.6a₀ 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.