Abstract Thermoluminescence in room-temperature X-irradiated KCl:Ag (14 ppm) crystals has been examined. KCI:Harshaw (nominal pure) crystals are also used for comparison. Stability of defects and kinetics of recombination processes occurring during thermoluminescence are investigated with a closer look at impurity effects. X-irradiations were performed at increasing doses (25 kV and 20 mA, 35 kV and 30 mA, 45 kV and 40 mA) for 5 h at each setting. Results indicate that the stability of defects in Ag-doped samples increases with dose. General-order kinetics methods indicate that recombination processes follow the first-order kinetics since the probability of retrapping (0.01) is far less than that of recombination (0.99). Using several first-order kinetics methods, the frequency factor seem to be in the region associated with escape frequency of electrons (10 9−10 12 s −1).