The radiation damage process in MgF2

F centre production by ionizing radiation in MgF 2 has a character which changes markedly with temperature; below approximately 50K and above approximately 200K essentially unsaturating defect production occurs while between approximately 50K and approximately 200K the concentration of F centres quickly saturates. Detailed measurements of the effect of irradiation intensity at 5K, 80K, and 300K have been made, together with measurements at constant intensity as a function of temperature. These results are interpreted in terms of a model in which the radiation creates close pairs of F centres and H centres which are stable at low temperatures, recombine at intermediate temperatures and dissociate at higher temperatures. Other evidence is presented for this model, including the fact that the observed F band is rather wider for F centres created at 5K than for centres created at 300K and measured at 5K.