RESUMEN
Raman analyzes were performed on zircon from a syenite located in the Poços de Caldas Complex, Brazil, with a fission-track (FT) zircon age of 81.4±6.8 Ma. Three isochronous heating (1, 10 and 100 hours) of zircon grains were subjected to temperatures between 300 and 750 °C. These temperature and times are usually applied to obtain zircon Fission-Track annealing dataset. For each time-temperature conditions, Raman spectra analyses were accomplished. The results show variations in the intensity and FWHM (full width at half maximum) in the main band (1007 cm-1- Si-O stretching mode), and a singular change in the peaks from 356 to 439 cm-1 (Si-O bending mode); and from 202 to 224 cm-1 (external modes). These changes were interpreted as spectral polarization-dependence related to common crystallinity increases due to the annealing radiation damages and that the thermal treatments do not interfere on the stability of zircon lattice.
RESUMEN
Characterization by micro-Raman spectroscopy of polymeric materials used as nuclear track detectors reveals physico-chemical and morphological information on the material's molecular structure. In this work, the nuclear track detector poly(allyl diglycol carbonate), or Columbia Resin 39 (CR-39), was characterized according to the fluence of alpha particles produced by a (226)Ra source and chemical etching time. Therefore, damage of the CR-39 chemical structure due to the alpha-particle interaction with the detector was analyzed at the molecular level. It was observed that the ionization and molecular excitation of the CR-39 after the irradiation process entail cleavage of chemical bonds and formation of latent track. In addition, after the chemical etching, there is also loss of polymer structure, leading to the decrease of the group density C-O-C (â¼888 cm(-1)), CH=CH (â¼960 cm(-1)), C-O (â¼1110 cm(-1)), C-O-C (â¼1240 cm(-1)), C-O (â¼1290 cm(-1)), C=O (â¼1741 cm(-1)), -CH2- (â¼2910 cm(-1)), and the main band -CH2- (â¼2950 cm(-1)). The analyses performed after irradiation and chemical etching led to a better understanding of the CR-39 molecular structure and better comprehension of the process of the formation of the track, which is related to chemical etching kinetics.
RESUMEN
Studies of zircon grains using optical microscopy, micro-Raman spectroscopy, and scanning electron microscopy (SEM) have been carried out to characterize the surface of natural zircon as a function of etching time. According to the surface characteristics observed using an optical microscope after etching, the zircon grains were classified as: (i) homogeneous; (ii) anomalous, and (iii) hybrid. Micro-Raman results showed that, as etching time increases, the crystal lattice is slightly altered for homogeneous grains, it is completely damaged for anomalous grains, and it is altered in some areas for hybrid grains. The SEM (energy dispersive X-ray spectroscopy, EDS) results indicated that, independent of the grain types, where the crystallinity remains after etching, the chemical composition of zircon is approximately 33% SiO(2):65% ZrO(2) (standard natural zircon), and for areas where the grain does not have a crystalline structure, there are variations of ZrO(2) and, mainly, SiO(2). In addition, it is possible to observe a uniform surface density of fission tracks in grain areas where the determined crystal lattice and chemical composition are those of zircon. Regarding hybrid grains, we discuss whether the areas slightly altered by the chemical etching can be analyzed by the fission track method (FTM) or not. Results of zircon fission track and U-Pb dating show that hybrid and homogeneous grains can be used for dating, and not only homogeneous grains. More than 50 sedimentary samples from the Bauru Basin (southeast Brazil) were analyzed and show that only a small amount of grains are homogeneous (10%), questioning the validity of the rest of the grains for thermo-chronological evolution studies using zircon FTM dating.