Luminescence from NaCl for application to retrospective dosimetry

The alkali halide NaCl (Common salt) is an environmentally-abundant phosphor of considerable potential for retrospective dosimetry and radiological event analysis due to its high sensitivity to ionising radiation when analysed by Thermoluminescence (TL), Optically-stimulated luminescence (OSL) or Infrared-stimulated luminescence (IRSL). We report here aspects of luminescence from NaCl relevant to the development of valid protocols for measurement of recent ionising radiation exposure. The timescale of interest in this application is from days to decades, hence our emphasis is on detection and characterisation of TL emission in the 100–300 °C range, and of OSL and IRSL emissions measured following only low temperature preheating (160 °C). A collection of 19 salt samples was assembled, including samples of rock salt and domestic salt produced by evaporation from brine. Analysis of TL emission spectral changes, together with previously reported TL, OSL and IRSL sensitivity changes, confirmed activation of sensitivity change by exposure to temperatures exceeding 160 °C. Kinetic analysis using Chen's method found E = 0.943 eV and s = 5.1 × 1011 s−1 for the 100 °C TL peak, giving a lifetime at 20 °C consistent with previous calculations and in the range of 7–14 h.

► Heating beyond ∼160 °C causes major sensitivity changes to TL and OSL.
► First report of creation of UV TL emission from NaCl by heating to and beyond 300 °C.
► TL peak at ∼100 °C (5 K/s), 590 nm emission, has lifetime at 20 °C of ∼9 h
► After heating to >240 °C, OSL and IRSL are not observed during stimulation at room temperature.