Monitoring of Radiation Defects Recovery in MgAl2O4 During Annealing by Optical Spectroscopy

Abstract

The extraordinary radiation resistance of single crystals and ceramics of magnesium-aluminum spinel to neutron irradiation is known, but the mechanisms that provide it are not yet understood. Irradiation of crystals with fast electrons creates defects partially similar to defects in neutron irradiation. The difference in the destructive effect is the significant level of ionization during electron irradiation. Therefore, to compare the results of irradiation by different sources, it is necessary to determine the parameters of radiation defects. One of them is the conditions of radiation damage recovery. When irradiating the crystals with electrons with an energy of 12.5 MeV to a fluence of 6.8∙1016 eV/cm2, the concentration of defects such as F-centers 2.6∙1016 cm-3 and V-centers 3∙1017 cm-3 was obtained. TSL and optical absorption spectroscopy methods were used to determine the state of radiation defects in crystals during annealing. Since annealing at temperatures above 900 K leads to complete discoloration of all optically active centers, therefore, to determine the effect of annealing at higher temperatures, the crystals after annealing were irradiated with ultraviolet light. At temperatures above 900 K, cationic disorder begins to increase, but annealing at 1010 K for 30 minutes was not enough to completely restore the damage to the crystal lattice created by electron irradiation. This is expected, given the characteristic relaxation time of cation disorder, which reaches 1000 hours at this temperature. However, increasing the annealing temperature to 1050 K, in addition to the recovery of radiation defects, creates a noticeable additional difference in TSL, probably due to the formation of complexes from residual F-centers. However, determining the difference between irradiated and non-irradiated crystals gives a difference in the concentration of F-centers at the level of 1015 cm-3.

Keywords

• spinel
• electron irradiation
• radiation defects
• annealing
• thermoluminescence