Simulation of optically-stimulated luminescence of zircon

Mineral zircon, ZrSiO4, belongs to a class of materials that can be used as a chronological tool in geology and archaeology for measurements of the natural radiation dose and the sample age by optical methods. The model of optically stimulated luminescence developed earlier is used to investigate the applicability of the single-aliquot regenerative-dose method (SAR) for dating with zircon. Various implementations of the SAR method are considered and practical recommendations are formulated.

Melting properties of radiation-induced Na and Cl2 precipitates in ultra-heavily irradiated NaCl

Exposure of NaCl to high doses of ionizing radiation leads to the formation of nano-particles of metallic Na, very small chlorine precipitates, vacancy voids, and dislocations. A useful way to monitor the stage of the damage formation process is measuring the latent heat of melting of the Na-particles (~100°C) and chlorine precipitates (-101°C). In this paper we will present data, showing that for doses in the range of TRad (1010 Gy) the concentration of radiolytic Na may become very large. Even in pure samples, we have converted more than 20% of all NaCl molecules into metallic Na and chlorine, but often higher percentages can be achieved. In this paper we will present new data obtained for ultra-high irradiation doses and a first attempt will be made to understand the results.

Nucleation and growth of sodium colloids in NaCl under irradiation: theory and experiment

A mechanism of radiation-induced emission of Schottky defects from extended defects proposed originally for metals has recently been applied to ionic crystals, where it is based on interactions of excitons with extended defects such as dislocations and colloids. Exciton trapping and decay at colloids may result in the emission of F centers and consequent shrinkage of the colloid. In the present paper, the radiation-induced emission of F centers is taken into account in the modeling of nucleation and growth of sodium colloids and chlorine bubbles in NaCl exposed to electron or gamma irradiation. The evolution of colloid and bubble number densities and volume fractions with increasing irradiation dose is modeled in the framework of a modified rate theory and compared with experimental data. Experimental values of the colloid volume fractions and number densities have been estimated on the basis of latent heat of melting of metallic Na obtained with combined differential scanning calorimetry experiments and atomic force microscopy investigations of metallic clusters.

Melting of sodium clusters in electron irradiated NaCl

In this paper we present the results of the first systematic investigation of the geometrical properties of sodium nanoclusters in NaCl using the combined results of differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The melting behaviour of the sodium nanoclusters which had been produced in NaCl by electron beam irradiation up to a dose of 200 MGy has been studied by means of DSC. The sodium colloids have been visualized by AFM and their size distribution has been evaluated for two irradiation doses. The DSC scans of the irradiated samples exhibit two melting peaks located at temperatures below the melting temperature of bulk sodium. A phenomenological model has been proposed which explains this behaviour by the existence of two different structural states in the population of sodium colloids. We believe that small sodium clusters inherit the FCC structure from the surrounding Na sublattice in the NaCl matrix. When a small colloid grows, its lattice structure eventually transforms into the BCC structure of bulk sodium. The model results have been compared with the DSC measurements and the transition radius for the two structural states has been estimated.

Thermoluminescence and optically stimulated luminescence of gamma-irradiated mineral zircon

Thermoluminescence (TL) manifested by gamma-irradiated mineral zircon has shown a strong TL peak at about 165 °C which is due to recombination of electrons and Dy3+ related shallow hole traps. After they have been removed by a short preheat we have observed two TL peaks at 300-320 °C and ≈420 °C, which are mainly due to recombination of electrons and Tb3+ related hole traps centres yielding its characteristic luminescence. The experimental results indicate that optically stimulated luminescence (OSL) is due to luminescent emission of Tb3+ ions and [SiO4]4– groups. The deep traps related to the 420 °C TL peak contribute to the Tb3+ related OSL. The deep traps related to the 300-320 °C TL peak contribute to OSL associated with the luminescent emission of [SiO4]4– groups.

Systematic UHV-AFM experiments on Na nano-particles and nano-structures in NaCl

Results of systematic AFM (atomic force microscopy) experiments on heavily and moderatly irradiated NaCl samples are presented. The sodium nanoparticles and structures of nanoparticles are poduced in sodium chloride during irradiation. The AFM images of the nanoparticles have been obtained in ultra high vacuum (UHV) in the non-contact mode with an Omicron UHV AFM/STM system. The sizes and arrangements of the observed particles depend on the irradiation conditions. The melting behaviour of the sodium nanoclusters has been studied for these samples by differential scanning calorimetry (DSC). A phenomenological model has been proposed which explains the observed behaviour by the existence of two different structural states in the population of sodium colloids. AFM measurements of heavily irradiated natural rock salt samples have revealed ring- and chain-like clusters (or agglomerates) of Na colloid particles.