Low-Temperature Annealing of the X-Ray-Induced Volume Expansion and Coloration of LiF

It has been shown previously that both ΔVV and the density of F centers produced by x irradiation of LiF at 80^∘{}K anneal out partially near 130^∘{}K. Upon reirradation at 80^∘{}K the F band quickly recovers while ΔVV does not recover. In the present study, an additional annealing stage of ΔVV and the F band was found near 270^∘{}K. Upon reirradiation at 80^∘{}K after annealing at 270^∘{}K, neither ΔVV or the F band recover in contrast to the recovery after annealing at 130^∘{}K. The irreversibility of the 270^∘{}K annealing of the F band indicates vacancy annihilation which apparently does not occur at 130^∘{}K. The formation of M centers at the higher temperature suggests vacancy motion. The fractional annealing at 130^∘{}K was found to be smaller than in previous work, presumably because of different sample perfection before irradiation.