Thermal spike effect on defect evolution in NaCl irradiated with light and heavy ions at 8 and 300 K

Single crystals of NaCl were irradiated at room temperature and at 8 K with energetic heavy ions (C-12, Ti-50, Ni-58, Kr-74, S-152,11, 197 An, Pb-208 and U-238) of 50-2600 MeV providing mean electronic energy loss values from 0.7 to 19 keV/nm. The creation and evolution of color centers were investigated as a function of fluence and temperature by in situ absorption spectroscopy and thermo-stimulated luminescence, complemented by thermal annealing and optical bleaching. For irradiations at 8 K, primary hole centers are observed which typically annihilate at temperatures between 10 and 80 K. The efficiency of color center creation at 8 K strongly depends on the energy loss of the ions and is several times higher for U and Au ions than for C and Ti ions. Thermal spike estimations, taking into account the finite velocity of heat propagation, assign these effects to thermal stimulated separation of color centers in the genetic Frenkel pairs. (c) 2005 Elsevier B.V. All rights reserved.