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1

Luminescence dating of volcanogenic outburst flood sediments from Aso volcano and tephric loess deposits, southwest Japan

Tsukamoto S., Kataoka K. S., Miyabuchi Y.

Geochronometria

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2013

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Vol. 40, no. 4

294--303

EN

Luminescence dating has been applied to volcanogenic outburst flood sediments (Takuma gravel bed) from Aso volcano, Japan, and tephric loess deposits overlying the gravel bed. The poly-mineral fine grains (4-11 μm) from loess deposits were measured with pulsed optically stimulated luminescence (pulsed OSL) and post-IR infrared stimulated luminescence (pIRIR) methods, whereas the Takuma gravel bed containing no quartz, was measured with IRSL and pIRIR methods using sand sized (150-200 μm) plagioclase. The loess deposits date back at least to ~50 ka by consistent IRSL, pIRIR and pulsed OSL ages from the lowermost part of the loess deposits from one section. The ages obtained from the bottom part of the other loess section are not consistent each other. However, we consider that the pIRIR age (72±6 ka) which showed negligible anomalous fading is most reliable, and regard as a preliminary minimum age of the Takuma gravel bed. The equivalent doses (De) for the plagioclase from the Takuma gravel bed have a narrow distribution and the weighted mean of the three samples yield an age of 89±3 ka. This age is in agreement with the last caldera-forming eruption of Aso volcano (~87 ka) and it is likely that the pIRIR signal has not been bleached before the deposi-tion. IRSL dating without applying pIRIR using small aliquots was also conducted, however, the IRSL signal shows no clear evidence of an additional bleaching during the event of outburst flood from the caldera lake.

2

Infrared stimulated luminescence (IRSL) properties of natural aluminum corrosion

Şahiner. E., Meriç N.

Geochronometria

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2012

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Vol. 39, no. 3

227-232

EN

In this paper, the infrared stimulated luminescence (IRSL) property of naturally corroded aluminum and its possible applications in retrospective dosimetry have been briefly studied. Results are interesting, in particular with regard to the efforts of finding new and widely available materials for accident dosimetry. For aluminum corrosion, the dose response was found to be approximately linear between 2-80 Gy and to reach saturation before 300 Gy. The signal also showed good repro-ducibility without significant fading over storage durations of up to four mounts at room temperature. In addition to the luminescence, the corrosion samples were also analysed by X-ray Fluorescence (XRF) and X-ray Diffraction (XRD), but conclusive identification of the luminescent phase could not be made. It is concluded that the IRSL signals of this material can be favourable for dosimetry research.

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Stability of IRSL signals from sedimentary K-feldspar samples

Thomsen K. J., Murray A. S., Mayank J.

Geochronometria

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2011

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Vol. 38, no. 1

1-13

EN

Recent work has identified IR stimulated luminescence signals at elevated temperature from both potassium- and sodium-rich feldspars that have much lower anomalous fading rates than the conventional signal measured using IR stimulation at 50°C. This paper examines the stability of these signals for potassium-rich sedimentary feldspars. We show that the natural post-IR IRSL (pIRIR) signal from a 3.6 Ma old sample is in apparent saturation on a laboratory generated dose response curve, i.e. it does not show detectable fading in nature although a low fading rate is observed on laboratory time scales. We show that the pIRIR signal has a greater thermal stability than the IRSL signal and that the trend in increasing thermal stability is mirrored by a decreasing fading rate. We also investigate the effect of preheat temperature and IR stimulation power on the decay shape and conclude that the data can be explained in terms of either a single- or multiple-trap model. We present evidence that may suggest that at least part of pIRIR signal is derived from a high temperature trap (~550°C thermoluminescence (TL) peak), although again the data can also be explained in terms of a single-trap model. Finally, we present dose response curves and characteristic curvature constants (D0) values for various IRSL signals and conclude that the more stable signals saturate more quickly than the less stable signals and that the initial and final signals saturate at approximately the same level.

4

Luminescence dating of young coastal deposits from New Zealand using feldspar

Madsen A. T., Buylaert J.-P., Murray A. S.

Geochronometria

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2011

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Vol. 38, no. 4

378-390

EN

A new measurement protocol has been tested on K-feldspars from Whanganui Inlet and Parengarenga Harbour, New Zealand. A Single Aliquot Regenerative (SAR) dose protocol, using two successive infrared (IR) stimulations (post-IR IR SAR protocol) is setup for these young (<1000 years) coastal sediments. Significant anomalous fading (g2days=7 %/decade) is observed using the conventional IR signal measured at 50°C. In contrast, the fading rate of the IR signal measured at elevated temperature (150°C) after the IR stimulation at 50°C (a post-IR IR signal) is not significant (g2days=7% /decade). Surprisingly low residual infrared stimulated luminescence (IRSL) signals were observed for a surface sample, suggesting that accurate ages as young as ~50 years can be obtained for these recent deposits. IRSL ages ranging between 48š6 years and 1050š50 years are obtained from six samples, indicating that sediment accumulation has occurred at the two sites during the last millennia, despite a falling trend in relative sea-level in Whanganui Inlet and a stable relative sea-level at Parengarenga Harbour.

5

IRSL and post-IR IRSL residual doses recorded in modern dust samples from the Chinese loess plateau

Buylaert J.-P., Thiel Ch., Murray A. S., Vandenberghe D. A. G., Yi S., Lu H.

Geochronometria

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2011

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Vol. 38, no. 4

432-440

EN

Using a set of modern/young (0 to about 200 years old) dust samples collected from the Chinese Loess Plateau the bleachability of IRSL measured at 50°C (IR50) and post-IR50 elevated temperature IRSL (measured at 225°C and at 290°C) is investigated by measuring the apparent (residual) doses recorded by these signals. Doses recorded by quartz OSL are used as a reference. Allowing for differences in dose rates it seems that both IRSL and post-IR IRSL signals yield residual doses that are significantly larger than the doses measured in quartz. These residual doses can be largely explained by thermal transfer caused by preheating. Nevertheless, we advise against the use of a low temperature preheat (<200°C) with IR50 to date loess samples because, as has been reported before, the signal appears to be thermally unstable. In general, we conclude that it may not be advisable to apply post-IR IRSL dating to Chinese loess samples where residuals of up to ~20 Gy are a significant fraction of the total dose. However, these residuals quickly become unimportant when dating older samples, and this is the age range in which post-IR IRSL dating is likely to be most useful.

6

Investigating the resetting of OSL signals in rock surfaces

Sohbati R., Murray A. S., Jain M., Buylaert J.-P., Thomsen K. J.

Geochronometria

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2011

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Vol. 38, no. 3

249-258

EN

There are many examples of buried rock surfaces whose age is of interest to geologists and archaeologists. Luminescence dating is a potential method which can be applied to dating such surfaces; as part of a research project which aims to develop such an approach, the degree of resetting of OSL signals in grains and slices from five different cobbles/boulders collected from a modern beach is investigated. All the rock surfaces are presumed to have been exposed to daylight for a prolonged period of time (weeks to years). Feldspar was identified as the preferred dosimeter because quartz extracts were insensitive. Dose recovery tests using solar simulator and IR diodes on both K-feldspar grains and solid slices taken from the inner parts of the rocks are discussed. Preheat plateau results using surface grains and slices show that significant thermal transfer in naturally bleached samples can be avoided by keeping preheat temperatures low. Equivalent doses from surface K-feldspar grains were highly scattered and much larger than expected (0.02 Gy to >100 Gy), while solid surface slices gave more reproducible small doses (mean = 0.17š0.02 Gy, n = 32). Neither crushing nor partial bleaching were found to be responsible for the large scattered doses from grains, nor did the inevitable contribution from Na-feldspar to the signal from solid slices explain the improved reproducibility in the slices. By modelling the increase of luminescence signal with distance into the rock surface, attenuation factors were derived for two samples. These indicate that, for instance, bleaching at a depth of 2 mm into these samples occurs at about ~28% of the rate at the surface. We conclude that it should be possible to derive meaningful burial doses of >1 Gy from such cobbles; younger samples would probably require a correction for incomplete bleaching.

7

The effect of thermal stimulation on the far-red and orange-red irsl signal of a french k-rich feldspar: preliminary results

Fattahi M.

Geochronometria

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2009

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Vol. 34

15-24

EN

Feldspar suffers from anomalous fading. Previous studies suggest that the level of fading depends on the emission band, and that the fading decreases by increasing the emission wavelengths; therefore, it is interesting to compare blue, orange and far-red IRSL emission characteristics. The purpose of this article is to make an initial consideration of some physical differences between two close emission windows. The effect of the sample temperature on far-red (λ >650 nm) and orangenear- red IRSL (λ =600-650 nm) from an identical feldspar sample is investigated. The difference in signal decay rate and thermal effects is discussed. While there is signal enhancement for far-red IRSL signals between 100-220° C, orange-near-red signals do not change. Some possible mechanisms for producing far-red and orange-near-red IRSL are discussed. This paper shows that orange-near-red IRSL and far-red IRSL thermal activation energies are different. This difference may be the cause of previously observed differences in stability of near and far-red IRSL signals.

8

Infrared Stimulated Luminescence and thermoluminescence dating of archaeological samples from Turkey

Meriç M., Atlihan M. A., Koşal M., Yüce. Ü R., Cinaroglu A.

Geochronometria

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2009

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Vol. 34

25-31

EN

In this study, the potential of Infrared Stimulated Luminescence (IRSL) and thermoluminescence (TL) for dating the archaeological samples (pottery sherds and soil sample adhered to surface of human bone) which were taken from a Necropolis was investigated. Archaeological sherds taken from Nusaybin (Mardin, Turkey), an archaeological site of archaic and Hellenistic period (from 330 BC to 30 AD), were dated. Samples were prepared by the fine grain technique and paleodose values were estimated by using multiple aliquot additive dose (MAAD) and single aliquot regenerative dose (SAR) procedures. The annual doses of uranium and thorium were determined by using the low level alpha counter. The potassium contents, which have no alpha activity, were determined by XRF equipment. The average age of the sherds were found to be 2375 ± 170 years which is in good agreement with the archaeological evidence involving architecture of castle wall, Necropolis and column sherds in the vicinity of the site.

9

Effects of feldspar contamination on equivalent dose and the shape of growth curve for osl of silt-sized quartz extracted from Chinese loess

Lai Z., Brückner H.

Geochronometria

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2008

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Vol. 30

49-53

EN

This study examines the effects of feldspar contamination of different extent (by fluorosilicic acid etching for different time periods and mixing pure quartz with different percentage of unetched grains) on blue-light stimulated luminescence (BLSL) of quartz (38-63 µm) for Chinese loess. In particular, the De values and the shape of growth curves will be examined. The results show that: (1) The De determined using feldspar in Chinese loess is obviously underestimated, and infra-red stimulated luminescence (IRSL) has a greater underestimation than BLSL. For aliquots with no fluorosilicic acid etching, an IRSL De underestimation of 󕾎% is observed for a sample with an expected age of 󕾆 ka, 󕾃% underestimation for BLSL, and 󕽺% for post-IR BLSL. For quartz BLSL, the contamination of feldspar, which has not dissolved by fluorosilicic acid etching, will inevitably lead to age underestimation. We suggest that the IR-checking should be performed for every single aliquot. An aliquot should be excluded from the final De calculation if obvious IRSL signal was observed. (2) For the sample under examination blue LED stimulation can reset both IRSL and BLSL signals of feldspars, while IR stimulation cannot reset the BLSL of feldspars. (3) For multiple-mineral aliquot the growth curve shape of the post-IR BLSL is different from that of the IRSL, and within 25 Gy it is identical to that of the pure quartz BLSL. The contamination of feldspars in quartz will change the shape of a growth curve for quartz BLSL.

10

A simple method to separate quartz and feldspar and its application to TL/OSL methods

Mosquera D. F., Sánchez J. S.

Geochronometria

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2008

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Vol. 30

41-47

EN

In the dating of sediments by luminescence methods, to obtain a sample the purest possible as to its mineralogy determines the rest of the analytical procedures. The isolation of the sample minerals is a critical stage due to the impossibility of quantifying the relative contributions to the dose from the different minerals. In this paper we propose a non chemical method to isolate quartz from feldspar extracted from different aeolian and fluvial sediments. Grinding together quartz and feldspar grains in an agate mortar results in crushing the feldspar fraction due to its smaller hardness. Later sieving of the grinded mixture enables simple separation of both fractions. Then it is possible to save the feldspar fraction for later analyses instead of losing it as it occurs when using acid etching. Also, we study the evolution of the feldspar abundance along different purification steps with acid etching or grinding with two numerical indexes. We conclude that the grinding procedure can be introduced in the purification methods as an effective way to separate quartz from feldspar. Nonetheless, it is not an standalone procedure to obtain pure quartz and must be combined with chemical methods when the sample is rich in feldspar minerals.