G. A. Wagner

New fission track ages of tektites and related glasses

Abstract Fission track dating is applied to a large number of australites, Muong Nong type tektites, Darwin glasses and Libyan Desert glasses. It is found that these glasses often have lowered fission track ages due to annealing effects. The same specimens have also smaller fission track etch pits. According to the diminishing percentage of etched fossil fission track diameters, lowered fission track ages are corrected. A mean age of 0.7 m.y. is found for eleven australites, six Darwin glasses and seven Muong Nong type tektites (from Laos and Thailand), indicating a related genesis of these glasses. Uncorrected fission track ages of five Libyan Desert glasses (26.6 −1.3 +6.3 m.y.) and two bediasites (33.2 1.2 +8.3 m.y.) are found to be different. With regard to these results an interrelationship between these two groups of glasses seems to be improbable.

The spontaneous fission rate of U-238 and fission track dating

Abstract The rate of spontaneous fission decay of uranium-238 (λf238) was determined in 4π-geometry by the fission track method. Uranium glasses of known age of manufacture were used. Spontaneous tracks have accumulated since the time of manufacture and induced tracks to determine the uranium content were produced by thermal neutron irradiations. Spontaneous tracks in all glasses were found to be partially annealed. By correcting for this annealing effect, a (λf238) = 8.7 ± 0.6 × 10−17yr−1 was obtained. Uncertainty in the neutron dose is the largest source of error.

Analysis of thermoluminescent glow peaks in quartz derived from the KTB-drill hole

Abstract The thermoluminescence of quartz sampled at various depths in the KTB-drill hole was studied. The trapping parameters, such as activation energy, frequency factor and kinetic order, were determined by different methods: peak shift with heating rate; initial rise; peak shape; isothermal decay. Lifetimes were calculated assuming first-order kinetics. The results are compared among the different methods and with values reported by other authors.

Monitoring environmental dose rate using Riso TL/OSL readers with built-in sources: recommendations for users

Abstract Measurements were carried out to quantify the dose rate delivered to samples due to leakage and cross-talk of the beta and alpha sources in various models of Riso TL/OSL readers; additionally the offset time was calculated. Highly sensitive α -Al 2 O 3 :C and CaF 2 :Mn dosemeters were used to investigate the impact on low environmental dose-rate assessment. The effect is shown to depend on the energy response of the detectors, the source strength and the reader design of the equipment. It was tested, if the scattered radiation of the closed source can be utilised to extend the dose range downwards to lower doses, as the dose rates of the built-in sources of Riso TL/OSL readers often exceed the practical values for ultra-low-dose measurements. The results and their consequences for environmental dose-rate assessment are discussed.

A study of thermoluminescence emission spectra and optical stimulation spectra of quartz from different provenances

The present study examines (1) variability in the thermoluminescence (TL) emission spectrum and optical stimulation (OSL) spectrum of quartz from different provenances and, (2) possible correlations between spectral features and the nature of the complex growth curves (ranging from saturating exponential to those described by a cubic polynomial function), so as to determine the validity of the currently used experimental protocols. The results suggest that commonly used UV emission for dating constitutes only a minor component of the total quartz emission and in view of this a dose-dependent contribution from blue/blue-green emission peak to the UV detection is likely. The OSL stimulation spectrum shows a definite change in stimulation response between 500-520 nm, hence implying that stimulation in this window may contribute as an additional source of scatter in multi-grain samples.

Shatter cones produced experimentally by impacts in limestone targets

Abstract Experimentally produced impact craters in limestone targets displayed millimeter-sized shatter cones within crater spallation zones. The craters have been produced by accelerating spherical metal projectiles by means of a light-gas gun. Variation of the impact velocity showed that at about 3 km/s shatter cone formation starts and is reproducible at any higher impact velocities. In most cases the cone apices were pointing in the direction of the impact center. The occurrence of shatter cones directly at the target surface (spallation zones of craters) does not support a theoretical model on shatter cone formation published by Gash (1971).

Silver sources of archaic Greek coinage

We report on new chemical and lead isotopic results and interpretations of archaic Greek silver coins from the Asyut hoard which was buried around 475 B.C. Aeginetan coins were of central interest in this study. Possible ancient silver mines were explored in the Aegean region in the course of several geologic expeditions, and chemically and isotopically investigated. Some of the silver sources in Greece were traced by combination of the analytical methods and questions of provenance were solved. In addition, processes of silver smelting and refining were studied. Results and implications of this work are summarized in the final section on Conclusions.

K-Ar and fission track dating of Darwin Crater Glass

Abstract Darwin Glasses from the recently discovered Darwin Crater in Tasmania were dated by the K-Ar and the fission track methods. The ages by both methods agree and yield a combined age of 0.73 ± 0.04 my for the formation of Darwin Crater and Darwin Glass by an impact. Since an accidental coincidence of this age with the age of Australasian tektites is rather unlikely, we suppose that Darwin Crater is one of many — primary or secondary — impact structures caused by the collision of a meteorite or comet with the earth ∼ 0.7 my ago in the region of South East Asia and Australia.

Thermoluminescence dating of loess deposits at plaidter hummerich and its implications for the chronology of Neanderthal man

Recent archeological investigations by the Forschungsstelle Altsteinzeit have shown that the crater hollows of extinct volcanoes in the Neuwied basin were regularly inhabited by Neanderthal man. A systematic search has yielded several sites, such as Plaidter Hummerich, T6nchesberg, the Wannen and the Wannenk6pfe, the Eiterk6pfe, and the Schweinskopf with a rich archeological ensemble related to the hunting activities of prehistoric man. At Plaidter Hummerich, much of this archeological material (bones and implements) has been found in situ in the loess beds that cap this volcano. We report here an absolute dating of these beds at Plaidter Hummerich based on recently developed thermoluminescence (TL) techniques [1, 2] for the dating of sediments. By virtue of the fact that these remains of Neanderthal man were found in situ, the loess TL ages provide perhaps a first absolute dating bracket (_<135000-80000a) to this developmental phase of mankind in the region. A date of 135000 a is also suggested for the recently discovered Kretzer tuff horizon in the Riss loess. The extinction of the Plaidter Hummerich volcano occurred ca. 240000 a ago [3]. At this stage, the crater summit was formed by a crater funnel surrounded by a steep wall of volcanic scoria. The infilling of the crater has continued since then, first in the form of crater rubble, derived from the rim, and subsequently by wind-blown loess. The entire sediment deposit (~15 m) is capped by the more recent (11000 a BP) Laacher See pumice [4]. Figures 1 and 2 provide a schematic diagram of the stratigraphy at the site. Loess ( < 9 m ) overlies the primary scoria and collapsed lava rubble. A still undescribed pumice, termed Kretzer tuff, subdivides this loess (Fig. 2, detail 1). On this loess a soil developed (weathered loess). The soil is separated from the overlying humus horizon ( < 2 m) by a calcified lava rubble or colluvium. The humus layer is inferred to correspond to the beginning of the Wfirmian [5] (Fig. 2, detail 2). A layer

Thermoluminescence studies on Jilin meteorite

Abstract The thermoluminescence (TL) of Jilin meteorite was measured as a function of depth (up to 21.7 mm) below the fusion crust using the 50–100 μm size fraction. Up to 6 mm depth, the natural TL increases steeply due to thermal draining during atmospheric passage resulting in a temperature gradient of 45°C/mm. Below 7 mm depth, a constant natural TL signal is observed corresponding to an equivalent dose of 3300 Gy. This quantity represents a lower limit for the total natural dose received by the meteorite. Assuming a dose rate of 0.1 Gy/a a minimum age of 33,000 years is calculated for the last thermal event ( 7 cm below the fusion crust).