Electron-Paramagnetic Resonance Absorption Studies of Neutron-Irradiated LiF at Temperatures Above 300°K

Electron-paramagnetic resonance (EPR) absorption of irradiated LiF has been investigated at controlled temperatures. The samples have received neutron doses ranging between 2.4×${10}^{15}$ and 1×${10}^{19}$ nvt. The temperature of the samples has been varied from 300° to near 600°K. The experimental results have indicated the need of distinguishing the following three neutron-dose ranges: a light-dose range (2.4×${10}^{15}$ nvt and probably less), a medium-dose range (2.4×${10}^{16}$ through 1×${10}^{18}$ nvt), and a heavy-dose range 1×${10}^{19}$ nvt and probably larger). The dependence of EPR spectra on the temperature has been described in terms of three characteristic temperatures $T_1$, $T_2$, and $T_3$. To explain the results, the two-center ${\mathrm{model}}^3$ has been adopted, and the activation energy for the diffusion of $F$ centers has been assumed to be dependent on the concentration of $F$ centers. Some difficulties, however, have been encountered in the application of the two-center model. A possible solution of these difficulties is considered.