Effects of X-irradiation in europium-doped NaCl

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Abstract
The first stage of F- and M-centre colouring has been investigated at room temperature in quenched samples of europium-doped NaCl as a function of the impurity concentration in the range 30-500 PPM. Attention has been paid to determine whether a correlation exists between the change in the concentration of Eu2+-cation vacancy dipoles and the colour centre formation in order to get a deeper insight into the nature of the interstitial halogen traps. The effects of x irradiation are (a) to reduce the number of (I-V) dipoles, (b) to increase the number of trapped electrons, (c) to convert the doubly valent europium ions to the monovalent, as well as to the tripositive state, and (d) to increase the rate of aggregation of dipoles. The number of dipoles destroyed by irradiation was found to be equal to or to exceed the sum of the number of europium ions which had changed their valence state and the number of F centres produced. The results presented in this paper suggest that the (I-V) dipoles act as the dominant traps for the radiation-induced interstitials. It was also ascertained that the M-centre density is proportional to the square of the F-centre density, the proportionality constant being clearly dependent on the inverse of the impurity concentration.