[en] Glow curves were recorded for NaCl:Sr²⁺ crystals subjected to annealing and quenching from elevated temperatures. These specimens were irradiated with X-rays at room temperature by tungsten target. Samples exhibit certain glow peaks which are observed only in the first thermal cycle. A marked difference in the glow curves pattern for first and subsequent thermal cycles has been observed. It is suggested that these changes may be due to the change in configurational coordinate system of F-centre due to impurity existing different states. This idea is supported by optical microscopy studies. (author)