U and Th thin film neutron dosimetry for fission-track dating: application to the age standard Moldavite

Iunes, P.J.; Bigazzi, G.; Neto, Júlio César Hadler; Laurenzi, M. A.; Balestrieri, Maria Laura; Norelli, P.; Araya, Ana Maria Osório; Guedes, S.; S., C.A. Tello; Paulo, S.R.; Moreira, P.A.F.P.; Palissari, Rosane; Curvo, Eduardo Augusto Campos

doi:10.1016/j.radmeas.2004.08.007

Cited by 7 publications

(7 citation statements)

References 14 publications

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“…[16] When the induced and spontaneous fission tracks are measured in the mineral itself, the method is called population method. [6] The zircon fission track ages are determined using a mathematical equation given by Iunes et al [17,18] Through FTM in zircon, both the age and the thermal events can be determined in regions of geological interest. Since the zircon closure temperature is ∼240 • C, which corresponds to the temperatures at which the tracks were retained in geological times, it is possible to determine ages close to the crystallization ages of some minerals.…”

Section: Introductionmentioning

confidence: 99%

Micro‐Raman spectroscopy and SEM/EDX applied to improve the zircon fission track method used for dating geological formations

Dias

Sáenz

Constantino

et al. 2008

J Raman Spectroscopy

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The zircon mineral is widely studied in geochronology. In the case of the fission track method (FTM), the age is determined by the density of fission tracks at the zircon surface, which can be observed with an optical microscope after an appropriate chemical treatment (etching). The etching must be isotropic at the zircon grain surface to be used in the FTM, which leads those zircon grains whose etching is anisotropic to be discarded. The only reason for this discarding is the nonuniform morphology of the surface grain seen by optical microscopy, that is, no further physicochemical analysis is performed. In this work, combining micro-Raman and scanning electron microscopy (SEM) to study the etching anisotropy, it was shown that zircon grains that present at least one area at the surface where the density of fission track is uniform can be used in the FTM. The micro-Raman showed characteristic spectra of the standard zircon sample either from the areas where there are tracks or from where there are not. The only difference found was in the Raman bandwidths, which were broader for the areas with higher density of fission tracks. This suggests simply a decrease in the relative percentage of the crystalline/amorphous phases at these areas. The SEM/energy dispersive spectrometry (EDX) showed that there were no significant differences in the principal chemical composition at the areas with and without fission tracks.

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Section: Introductionmentioning

confidence: 99%

Micro‐Raman spectroscopy and SEM/EDX applied to improve the zircon fission track method used for dating geological formations

Dias

Sáenz

Constantino

et al. 2008

J Raman Spectroscopy

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“…Samples were irradiated at the IEA-R1 reactor (IPEN/CNEN, São Paulo, Brazil) using standard glasses (CN5), calibrated through natural uranium thin films, as dosimeters (Bigazzi et al 2000;Iunes et al 2002Iunes et al , 2004Iunes et al , 2005. The neutron fluence was measured using the calibration by natural uranium thin film yielding the value of f = 2.2 × 10 15 neutrons/cm 2 .…”

Section: Methodsmentioning

confidence: 99%

Further investigation of the initial fission-track length and geometry factor in apatite fission-track thermochronology

Soares

Guedes

Tello

et al. 2013

American Mineralogist

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The external detector method (EDM) is a widely used technique in fission track thermochronology (FTT) in which two different minerals are concomitantly employed: spontaneous tracks are observed in apatite and induced ones in the muscovite external detector. They show intrinsic differences in detection and etching properties that should be taken into account. In this work, new geometry factor values, g, in apatite, were obtained by directly measuring the r ed /r is ratios and independently determined [GQR] ed/is values through the measurement of projected lengths. Five mounts, two of which were large area prismatic sections and three samples composed of random-orientation pieces have been used to determine the g-values. A side effect of applying EDM is that the value of the initial confined induced fission track, L 0 , is not measured in routine analyses. The L 0 -value is an important parameter to quantify with good confidence the degree of annealing of the spontaneous fission tracks in unknown-age samples, and is essential for accurate thermal history modeling. The impact of using arbitrary L 0 -values on the inference of sample thermal history is investigated and discussed. The measurement of the L 0 -value for each sample to be dated using an extra irradiated apatite mount is proposed. This extra mount can be also used for determining the g value as an extension of the r ed / r is ratio method. Eight apatite samples from crystalline basement, with grains at random orientation, were used to determine the g-values. The results found are statistically in agreement with the values found for apatite samples (from Durango, Mexico) measured in prismatic section and also measured at random orientation. There was no observable variation in efficiency regarding crystal orientation, showing that it is relatively safe using non-prismatic grains, especially in samples with paucity of grains, as it is the case of most basin samples. Implications for the z-calibration and for the calibration of the direct (spectrometer-based) fission-track dating are also discussed.

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“…Our result, 29.7 ± 1.1 Ma, was consistent with the recommended reference age, 31.44 ± 0.18 Ma, obtained from 40 Ar/ 39 Ar sanidine ages of geological units bracketing the Durango apatite deposit (McDowell et al 2005). Two Moldavites from the Middle Miocene deposit of Jankov (Balestrieri et al 1998, Bouska 1994, Bouska et al 2000 irradiated in three reactors, yielded apparent ages of 13.1 ± 1.0 and 13.66 ± 0.87 Ma and plateau ages Poupeau 1973, Westgate 1989) ranging from 12.23 ± 0.92 up to 16.5 ± 2.2 Ma, with an average of 13.89 ± 0.53 Ma (Iunes et al 2005). Two Macusanites from river banks at Chilcuno Chico (Poupeau et al 1992(Poupeau et al , 1993 were repeatedly analysed using six irradiations in three reactors.…”

Section: Fission-track Datingmentioning

confidence: 98%

“…Several FT age determinations were recently performed on Moldavite and Macusanite samples using an absolute calibration approach with neutron dosimetry based on U and Th thin films (Iunes et al 2005, Osorio et al 2003. show that the use of natural U and Th thin films can be an efficient alternative to provide accurate neutron fluence determinations.…”

Section: Fission-track Datingmentioning

confidence: 99%

New Constraints on Ages of Glasses Proposed as Reference Materials for Fission‐Track Dating

Laurenzi

Balestrieri

Bigazzi

et al. 2007

Geostandard Geoanalytic Res

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New analyses have been performed in order to enhance the data‐set on the independent ages of four glasses that have been proposed as reference materials for fission‐track dating. The results are as follows. Moldavite ‐ repeated 40Ar/39Ar age determinations on samples from deposits from Bohemia and Moravia yielded an average of 14.34 ± 0.08 Ma. This datum agrees with other recent determinations and is significantly younger than the 40Ar/39Ar age of 15.21 ± 0.15 Ma determined in the early 1980s. Macusanite (Peru) ‐four K‐Ar ages ranging from 5.44 ± 0.06 to 5.72 ± 0.12 Ma have been published previously. New 40Ar/39Ar ages gave an average of 5.12 ± 0.04 Ma. Plateau fission‐track ages determined using the IRMM‐540 certified glass and U and Th thin films for neutron fluence measurements agree better with these new 40Ar/39Ar ages than the previously published ages. Roccastrada glass (Italy) ‐ a new 40Ar/39Ar age, 2.45 ± 0.04 Ma, is consistent with previous determinations. The Quiron obsidian (Argentina) is a recently discovered glass that has been proposed as an additional reference material for its high spontaneous track density (around 100 000 cm‐2). Defects that might produce “spurious” tracks are virtually absent. An independent 40Ar/39Ar age of 8.77 ± 0.09 Ma was determined and is recommended for this glass. We believe that these materials, which will be distributed upon request to fission‐track groups, will be very useful for testing system calibrations and experimental procedures.

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U and Th thin film neutron dosimetry for fission-track dating: application to the age standard Moldavite

Cited by 7 publications

References 14 publications

Micro‐Raman spectroscopy and SEM/EDX applied to improve the zircon fission track method used for dating geological formations

Micro‐Raman spectroscopy and SEM/EDX applied to improve the zircon fission track method used for dating geological formations

Further investigation of the initial fission-track length and geometry factor in apatite fission-track thermochronology

New Constraints on Ages of Glasses Proposed as Reference Materials for Fission‐Track Dating

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