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ABSTRACT: 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 (∼888 cm(-1)), CH=CH (∼960 cm(-1)), C-O (∼1110 cm(-1)), C-O-C (∼1240 cm(-1)), C-O (∼1290 cm(-1)), C=O (∼1741 cm(-1)), -CH2- (∼2910 cm(-1)), and the main band -CH2- (∼2950 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.
Applied Spectroscopy 04/2013; 67(4):404-8. · 1.66 Impact Factor
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ABSTRACT: 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.
Applied Spectroscopy 05/2012; 66(5):545-51. · 1.66 Impact Factor
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ABSTRACT: As a consequence of thermal treatment, fission tracks are shortened and a reduction of the surface density is expected, implying in a reduction of the fission-track age. Geometric considerations predict a linear relationship between track shortening and surface density reduction. However, experimental results for apatite, zircon and titanite found in literature, show a deviation from this relationship. Observation efficiency, crystallographic orientation, track segmentation and biases in length measurements have been invoked in order to explain the experiments, but do not succeeded in this aim. In this work, a model relating etching efficiency (via critical angle) with the amount of lattice defect (via mean track length) is proposed. It is assumed that the chemical etching obeys a rate law and that the observable means of densities and lengths are the net result from the mean actions of the orientation-dependent track and bulk etching velocities. The result is a two-parameter kinetic model described by the equationwhere k and n are parameters related to the particular characteristics of the minerals. The model fits quite well the experimental data, showing that the general model principles (hypotheses and simplifications), provide a good general description of the processes causing the deviation detected by the experiments. The presented model does not discard, but embrace the previous attempts of explaining the relationship between fission-track lengths and densities.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 217(4):627-636. · 1.21 Impact Factor
