Production of Colloidal Sodium in NaCl by Ionizing Radiation

A study has been made of the coloration of synthetic and natural sodium chloride crystals with ${\mathrm{Co}}^{60}$ gamma-ray and 1.3-Mev electron irradiations. These irradiations produced the colloid band, at 565 mμ, in the synthetic crystals but not in untreated natural crystals. Various thermal treatments were given the natural crystals prior to their coloration. It was found that either type of irradiation would produce colloids in crystals that had been heated at 700°C for at least 24 hours in an atmosphere containing hydroxyl ions. Colloids were produced in the untreated natural crystals by additive coloration. It was found that the characteristics of the colloids were the same whether they were produced by ionizing radiation or by additive coloration, with the exception of the role played by hydroxyl ions in the crystals colored by ionizing radiation.