Investigation on thermally assisted optically stimulated luminescence (TA - OSL) signal in various sodium chloride samples

Sodium chloride (NaCl) is a phosphor with potential significance in retrospective dosimetry and geological dating. NaCl has been extensively studied for practical use in OSL dosimetry, however, the exact mechanism of the OSL emission is not well explained. This work attempts to extend the information on NaCl luminescent properties by establishing the occurrence of very deep traps in NaCl using the thermally assisted OSL (TA OSL) method. The studied material was sodium chloride in different forms: halite minerals from Klodawa salt mine in Poland and NaCl in chemically pure form. The isothermal TA OSL signal was measured at various temperatures between 25 degrees C and 280 degrees C after a prior irradiation and TL erasing of shallow and main traps. The appearance of a strong TA OSL signal indicates the occurrence of very deep traps in all forms of investigated salt. The temperature dependence of TA-OSL was determined and the activation energy for thermal assistance corresponding to deep traps in NaCl was estimated. For selected temperatures of TA OSL readout (200 degrees C and 280 degrees C) the dose response was examined in wide dose range (1-1000 Gy). Sublinearity was found in different dose range depending on the type of samples.