Modelling the effective atomic number and the packing factor of polyatomic compounds: Applications to refractive index and dosimetry

•An analytical expression to predict the effective atomic number of any ionic compound is being announced.•An effective distance between the positive and negative centre of charge is being postulate.

In this work, based on fundamental physics and chemistry (charge distribution, electronegativity, induced dipole moment), we are introducing an analytical expression for ZeffZeff and a general way of calculating the crystal packing factor, p, of any ionic material. By using the average separation between the atomic and crystal(ionic) radii of the interacting ions, we are postulating an effective distance  (Rij)(Rij) between the positive and the negative centre of charge. When compared to the available experimental data, predictions within 20% have been obtained to ZeffZeff of materials applied to dosimetry. In photonics, the increasing behaviour of the refractive index with ZeffZeff is confirmed. By combining crystal field and effective charge models, we have predicted ZeffZeff of the Eu2O3 within the range of available experimental data.