Thermoluminescence and Color Center Correlations in Dosimetry LiF

Abstract

Dosimetry LiF was γ irradiated up to 10 000 R, and the resulting thermoluminescence was studied above room temperature in conjunction with the optical absorption between 190 and 400 nm. Changes in the glow curves and absorption spectra after various optical and thermal treatments show that the thermoluminescence process begins with thermal release of electrons from centers causing optical absorption in the 310–380‐nm region. Moreover, the centers causing the important dosimetry glow peaks near 200°C appear to have two excited states, so that these centers have optical absorption bands at both 310 nm and under the F band at 250 nm. In particular two glow peaks near 200°C are correlated with two 310‐nm absorption bands which are distinguished by different optical bleaching rates. For the glow peak usually used for dosimetry, the correlation is supported by an equality of thermal activation energies for the glow peak and 310‐nm band. To interpret all the data in terms of these correlations requires assuming a restriction in the availability of luminescence sites. Implications for the photon production mechanisms and the trap structures are discussed. An asymmetry in the F band of LiF, as if a large K band were present, is also found.