Using interaction potentials screened with the Debye-Huckel length, the effects of plasma shielding on energy levels and electrons scattering from neutral and ionized caesium are estimated. Both energy levels and atomic scattering cross-sections are found to be sensitive to the inclusion of screening. Relating to the scattering by the Csf ion, a low-energy resonance near E = 0.3 Ryd is foupd which arises from the f-wave phase shift and reflects the individual behaviour of the scnttering ion.