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The mineral zircon, ZrSiO 4 , belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such a model. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time annealing at a given temperature. (iv) Heating of the irradiated sample to simulate TL experiments both after laboratory and natural irradiation. The input parameters of the model, such as the types and concentrations of the TL centres and the energy distributions of the hole and electron traps, were obtained by analysing the experimental data on fading of the TL-emission spectra of samples from different geological locations. Electron paramagnetic resonance (EPR) data were used to establish the nature of the TL centres. Glow curves and 3D TL emission spectra are simulated and compared with the experimental data on time-dependent TL fading. The saturation and annealing behaviour of filled trap concentrations has been considered in the framework of the proposed kinetic model and compared with the EPR data associated with the rare-earth ions Tb 3+ and Dy 3+ , which play a crucial role as hole traps and recombination centres. In addition, the behaviour of some of the SiO n− m centres has been compared with simulation results.

In heavily irradiated NaCl explosions can be initiated during irradiation or later, after the irradiation, when the samples are heated to temperatures in the range 100-250°C. As a result of the irradiation Na and C12 precipitates, dislocations and voids are produced, along with stored energy (the maximum value observed until now N 76 kJ/mol, which is about 18.5% of the enthalpy of formation of NaCI, 411.2kJ/mol). This implies that heavily irradiated NaCl is a highly energetic material. We have observed that the samples, which revealed large radiation-induced voids, explode rather easily. In these samples the instability connected with large voids (hot spots) probably initiates the explosive release of stored energy, which is in many cases accompanied by characteristic (explosive) sounds. In this paper we will discuss the nature of the explosions and show that a basically stable insulating compound, such as NaCI, may become unstable after heavy irradiation.

Electron spin resonance and nuclear magnetic resonance of sodium macrostructures in strongly irradiated NaCl-K crystals: Manifestation of quasi-one-dimensional behavior of electrons.

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