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 degrees C range, and of OSL and IRSL emissions measured following only low temperature preheating (160 degrees 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 degrees C. Kinetic analysis using Chen's method found E = 0.943 eV and s = 5.1 x 10(11) s(-1) for the 100 degrees C TL peak, giving a lifetime at 20 degrees C consistent with previous calculations and in the range of 7-14 h. (C) 2012 Elsevier Ltd. All rights reserved.