Effects of Etching on Zircon Grains and Its Implications for the Fission Track Method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)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% SiO2:65% ZrO2 (standard natural zircon), and for areas where the grain does not have a crystalline structure, there are variations of ZrO2 and, mainly, SiO2. 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 (FM) or not. Results of zircon fission track and U-Ph 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.665545551Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Comparison of population and external detector method dating in epidote

Epidote fission-track dating (FTD) was performed through both Population and external detector method (EDM) in five samples from the Mantiqueira Mountain range, southwestern Brazil. The ages obtained via population conducted to a weighted mean age of (114 +/- 19) Ma. In order to perform EDM dating, it was necessary to measure the efficiency factor (g) between muscovite mica and epidote. Three measurements were performed and the weighted mean g value obtained was (0.57 +/- 0.03). The weighted EDM age was (98 +/- 7) Ma. The population error magnitude occurs due to the existence of few useful epidote grains. EDM provides dating with fewer grains, however there are difficulties concerning etching anisotropy that should be regarded. Both dating methods agreed. (c) 2007 Elsevier Ltd. All rights reserved.4281307131

Extrapolation of zircon fission-track annealing models

One of the purposes of this study is to give further constraints on the temperature range of the zircon partial annealing zone over a geological time scale using data from borehole zircon samples, which have experienced stable temperatures for similar to 1 Ma. In this way, the extrapolation problem is explicitly addressed by fitting the zircon annealing models with geological timescale data. Several empirical model formulations have been proposed to perform these calibrations and have been compared in this work. The basic form proposed for annealing models is the Arrhenius-type model. There are other annealing models, that are based on the same general formulation. These empirical model equations have been preferred due to the great number of phenomena from track formation to chemical etching that are not well understood. However, there are two other models, which try to establish a direct correlation between their parameters and the related phenomena. To compare the response of the different annealing models, thermal indexes, such as closure temperature, total annealing temperature and the partial annealing zone, have been calculated and compared with field evidence. After comparing the different models, it was concluded that the fanning curvilinear models yield the best agreement between predicted index temperatures and field evidence. (c) 2012 Elsevier Ltd. All rights reserved.50SI19219

Micro-Raman Spectroscopic Characterization of a CR-39 Detector

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)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 Ra-226 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 (similar to 888 cm(-1)), CH=CH (similar to 960 cm(-1)), C-O (similar to 1110 cm(-1)), C-O-C (similar to 1240 cm(-1)), C-O (similar to 1290 cm(-1)), C=O (similar to 1741 cm(-1)), -CH2- (similar to 2910 cm(-1)), and the main band -CH2- (similar to 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.674404408Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Annealing experiments on induced fission tracks in apatite: Measurements of horizontal-confined track lengths and track densities in basal sections and randomly oriented grains

To improve kinetic models for apatite fission-track annealing, we present new experimental annealing data that complement previously published data. To determine the degree of annealing of induced tracks, surface density (p), and mean horizontal-confined track lengths (1). were measured, both for basal and randomly oriented faces. Our annealing data were obtained by submitting an apatite sample collected in ltambe, Bahia, Brazil, to 46 different isothermal treatments where temperature ranged from 150 to 600 degrees C (duration of 1, 10, 100, and 1000 h). To compare the behavior of Itambe to Durango apatite, the latter was also annealed for I h in 9 isothermal experiments at temperatures between 240 and 380 degrees C. Our results show that the l/l(0) values in Durango are systematically smaller than those in Itambe sample, both in basal and random faces. The curves depicting relative track density reduction, rho/rho(0), and relative mean confined track length reduction, l/l(0), as a function of time and temperature, are similar for rho/rho(0) > similar to 0.5, but different for rho/rho(0) < similar to 0.5. In this interval, rho/rho(0),can be measured but the measurement of l/l(0) is very difficult because the confined tracks become undetectable. Measurements of rho/rho(0) and l/l(0) for tracks revealed in basal surfaces are systematically lower (but this difference is < 3%) than those in randomly oriented ones.914170025226

Anisotropy of track revelation in epidote: Results of a step etching experiment with Kr-86 ion tracks

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Epidote etching anisotropy has been studied through step etching of Kr-86 (300 MeV) ion tracks. A slice of epidote natural monocrystal was taken from the (010) plane and then divided into five pieces. Each piece was then irradiated with ions whose incidence angles (zenith angles) were of 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees with respect to y-axis. The azimuthal angle of incidence of the ions was the same for the pieces 15 degrees, 60 degrees, 75 degrees and 180 degrees apart for the pieces 30 degrees and 45 degrees. Etching times were of 10, 20, 30, 40 and 50 min (HF 40%, 35 degrees C). The results show that etching velocities of ion tracks are higher in directions closer to the y-axis. The mean lengths of the ion tracks, regarding the angles, were of 23.14 +/- 0.21 (15 degrees); 19.89 +/- 0.08 (30 degrees); 19.39 +/- 0.04 (45 degrees) and 16.59 +/- 0.10 mu m (60 degrees). Since no tracks were identified in the 75 degrees aliquot it was assumed that the epidote has a critical angle, for recording of ion tracks with this mass/energy ratio, between 60 degrees and 75 degrees. (C) 2011 Elsevier Ltd. All rights reserved.468722725Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

On the annealing of fission tracks in randomly oriented grains of apatite

Apatite fission-track thermochronology has been based upon measurements in prismatic sections. Until now, all annealing data sets referred to this kind of measurement. However, prismatic sections are not always available, e.g. for detrital apatite grains, making the work impossible. An alternative would be to use grains in any orientation. This requires that a suitable annealing model be employed, i.e. one obtained from measurements in grains without preferential orientation. In this work, the angular distribution of confined fission tracks parallel to the surfaces of grains randomly oriented relative to the crystallographic c-axis is obtained. This distribution shows that track at higher angles relative to c-axis, when compared with the prismatic section distribution, are found. The procedure measurements in randomly oriented sections is presented along with empirical model equations. Model parameters have been obtained for the most common empirical equations and the partial annealing zone has been calculated for these equations. Results are compared with geological benchmarks; the fanning linear Arrhenius model yields the best agreement. This empirical model and those most used in literature have been applied to samples from the Sao Francisco Craton, Brazil, to show an instance in which the effects of grain orientation is important. Thermal histories of geological samples have been obtained through these equations. The samples tested presented moderate annealing and experienced a relatively simple thermal history. Under these conditions, taking into account the uncertainties in the model equations and confined track measurements, and using compatible systems, the presented model equations and the most used prismatic face ones constrained the same thermal history feature. (c) 2007 Elsevier B.V. All rights reserved.256268369

A comparison between neutron-fluence measurements using metal-activation monitors and standard glasses calibrated via thin uranium-fission monitors and via eta q method

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The two fundamental approaches to fission-track dating involve either an explicit determination of the thermal neutron fluence (phi-method) or a calibration against age standards (zeta-method). The neutron fluence measurements are carried out with metal-activation monitors or with uranium-fission monitors, co-irradiated with the samples. Uranium-fission monitors consist of either a thin "mono-atomic") film, or a thick fission source (standard uranium glass) irradiated against a muscovite external track detector. In this work, different techniques for performing neutron-fluence measurements were compared: based on thin-film calibration, based on thick-source calibration, and based on gamma spectrometry of co-irradiated metal monitors (Au, Co). The results suggest that more experiments are needed to make all calibrations consistent, including new measurements of the length of etched induced tracks in mica. Also the standard glass calibration carried out with thin films should be confirmed with a greater number of calibrating irradiations. (c) 2013 Elsevier Ltd. All rights reserved.53-543844Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CAPES [4143-06-0]FAPESP [2005/01684-4

Boron thin films and CR-39 detectors in BNCT: A method to measure the B-10(n,alpha)Li-7 reaction rate

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The working principle of the Boron Neutron Capture Therapy (BNCT) is the selective delivery of a greater amount of boron to the tumor cells than to the healthy ones, followed by the neutron irradiation that will induce the emission of alpha-particles and recoil Li-7 nuclei through the B-10(n,alpha)Li-7 reaction. The objective of this work is to present a setup composed of a boron thin film coupled with CR-39. Alpha and Li-7 particle coming from the boron films are used to quantify neutron boron reaction and are detected by CR-39. The nuclei compounding of this detector, H, C and O, will undergo fast neutrons reactions, which will be detected in the CR-39 itself. In this way, the B-10(n,alpha)Li-7 reaction and the contribution of fast neutrons to the flux can be determined at the same time. These measurements are essential for treatment planning as well as for studies of the biodistribution of B-10-carrier drugs and tissue microdosimetry. The boron films were deposited on stainless steel substrates through the sputtering technique and irradiated with thermal neutrons at the reactor lEA-R1 located at IPEN, Sao Paulo/SP, Brazil. Here we show the first results on the characterization of these thin films and calibration of the proposed setup. (c) 2012 Elsevier Ltd. All rights reserved.50SI181186Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES