Annealing of radiation induced oxygen deficient point defects in amorphous silicon dioxide:evidence for a distribution of the reaction activation energies

Abstract

The selective annealing of point defects with different activation energies is studied, by performingsequences of thermal treatments on gamma irradiated silica samples in the temperature range300–450 °C. Our experiments show that the dependence on time of the concentration of two irradiationinduced point defects in silica, named ODC(II) (standing for oxygen deficient centre II) and theEγ′ centre, at a given temperature depends on the thermal history of the sample forboth of the centres studied; moreover in the long time limit this concentrationreaches an asymptotic value that depends on the treatment temperature alone.These results suggest the existence of a distribution of the activation energies of thereaction process responsible for the annealing of the defects investigated, intimately relatedto the intrinsic disorder of the amorphous lattice. Furthermore, our data show that thethermal treatment can modify this distribution of activation energies and as a consequencethe thermal properties of the centre itself.