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Advances in accelerator mass spectrometry have resulted in an unprecedented amount of new high-precision radiocarbon (14C) -dates, some of which will redefine the international 14C calibration curves (IntCal and SHCal). Often these datasets are unaccompanied by detailed quality insurances in place at the laboratory, questioning whether the 14C structure is real, a result of a laboratory variation or measurement-scatter. A handful of intercomparison studies attempt to elucidate laboratory offsets but may fail to identify measurement-scatter and are often financially constrained. Here we introduce a protocol, called Quality Dating, implemented at ETH-Zürich to ensure reproducible and accurate high-precision 14C-dates. The protocol highlights the importance of the continuous measurements and evaluation of blanks, standards, references and replicates. This protocol is tested on an absolutely dated German Late Glacial tree-ring chronology, part of which is intercompared with the Curt Engelhorn-Center for Archaeometry, Mannheim, Germany (CEZA). The combined dataset contains 170 highly resolved, highly precise 14C-dates that supplement three decadal dates spanning 280 cal. years in IntCal, and provides detailed 14C structure for this interval.
The modern antiquities market uses radiocarbon (14C) dating to screen for forged objects. Although this fact shows the potential and power of the method, the circumstances where it is applied can be questionable and call for our attention. Here we present an outline of a call to radiocarbon laboratories for due diligence and best practice approaches to the analysis of antique objects requested by non-research clients.
Lead white is a man-made white pigment commonly used in works of art. In this study, the possibility of radiocarbon dating lead white pigments alone and in oil paints was explored using well-dated lead white pigments and paints. Resulting 14C ages on lead white pigments produced following the traditional stack process, where carbonate groups results from the incorporation of CO2 originating from fermentation, matched the production years, while radiocarbon dating of lead white made using other industrial processes indicate that 14C depleted CO2 was used in their production. The method was applied to two case studies, where lead carbonate samples were dated in two oil paintings, one Baroque and one from the 20th century. We hereby show that the lead white pigment can be dated by 14C and used as proxy for the time of creation of an artwork. Additionally, a two-step method was developed to allow 14C analysis of both the lead white pigment and oil binder from the same sample. A single lead white paint sample can yield two distinct radiocarbon ages, one from the carbonate and one from the natural organic binder. This study thus proposes new strategies for 14C dating of artworks.
The use of accelerator mass spectrometry (AMS) for age determinations of paintings is growing due to decreasing sample size requirements. However, as only the support material is usually dated, the validity of the results may be questioned. This work describes a novel sampling and preparation technique for dating the natural organic binder using radiocarbon (14C) AMS. In the particular case of oil paintings, the natural oil used has a high probability of being representative of the time of creation, hereby circumventing the problem of the originality of the support material. A multi-technique approach was developed for a detailed characterization of all paint components to identify the binder type as well as pigments and additives present in the sample. The technique was showcased on a painting of the 20th century. The results by 14C AMS dating show that both the canvas and binding medium predate the signed date by 4–5 yr. This could be the time span for keeping painting material in the atelier. The method developed provides, especially given the low amounts of material needed for analysis, a superior precision and accuracy in dating and has potential to become a standard method for oil painting dating.
Radioisotopes (239Pu, 240Pu, 236U) formed during atmospheric nuclear weapons testing (NWT) can be used for dating and therefore be applied as markers of the beginning of the Anthropocene Epoch. Moreover, 240Pu/239Pu ratios enable source identification (general fallout, local emission sources). Ice core segments from a 57.6 m ice core to bedrock from eastern Tien Shan, China were selected for 239,240Pu and 236U analyses by using compact low-energy accelerator mass spectrometry. The observed 240Pu/239Pu atom ratios were 0.18 ± 0.02, with one exception, indicating global fallout. No evidence for emissions from the nearby local sources Lop Nor was observed. The total deposition rates during NWT for 239Pu and 240Pu amount to 1.55 × 109 atoms·cm−2 and 3.1 × 108 atoms·cm−2, respectively. With the higher undisturbed fallout of 239Pu compared with values reported for glaciers from European Alps at Col du Dome and Colle Gnifetti as well as from the polar region, the eastern Tien Shan glacier would be an ideal site for defining the start of the Anthropocene. 236U is a rather new environmental tracer, while little is known about its global fallout from NWT. The observed deposition flux of 236U during NWT amounts to 3.5 × 108 atoms·cm−2 at the drill site. The average 236U/239Pu ratio of 0.27 ± 0.09 is in good agreement with literature values from global fallout.
Substances enriched with radiocarbon can easily contaminate samples and laboratories used for natural abundance measurements. We have developed a new method using wet chemical oxidation for swabbing laboratories and equipment to test for 14C contamination. Here, we report the findings of 18 months’ work and more than 800 tests covering studies at multiple locations. Evidence of past and current use of enriched 14C was found at all but one location and a program of testing and communication was used to mitigate its effects. Remediation was attempted with mixed success and depended on the complexity and level of the contamination. We describe four cases from different situations.
Studies using carbon isotopes to understand the global carbon cycle are critical to identify and quantify sources, sinks, and processes and how humans may impact them. 13C and 14C are routinely measured individually; however, there is a need to develop instrumentation that can perform concurrent online analyses that can generate rich data sets conveniently and efficiently. To satisfy these requirements, we coupled an elemental analyzer to a stable isotope mass spectrometer and an accelerator mass spectrometer system fitted with a gas ion source. We first tested the system with standard materials and then reanalyzed a sediment core from the Bay of Bengal that had been analyzed for 14C by conventional methods. The system was able to produce %C, 13C, and 14C data that were accurate and precise, and suitable for the purposes of our biogeochemistry group. The system was compact and convenient and is appropriate for use in a range of fields of research.
The looting of archaeological and ethnographic objects from emerging countries and areas of conflict has prospered due to the high prices that these objects can achieve on the art market. This commercial value now almost necessarily requires proof of authenticity by the object’s age. To do so, absolute dating has been conducted since the end of the 1970s on terra cotta art objects using the thermoluminescence method, a practice that has since been condemned. It is only more recently, since the 2000s, that art dealers and collectors have begun to use the accelerator mass spectrometry (AMS) method to date different kinds of objects made of organic materials. Compared to conventional radiocarbon dating, the AMS technique requires only very small samples, thus depreciating neither the aesthetics nor commercial value of the object. As a result, the use of absolute dating has become widespread, accompanying the increase in looting of the cultural heritage of countries destabilized by political overthrows and armed conflicts, especially in the Near East and Africa. The present article condemns the practice of AMS dating of looted art objects and encourages the creation of a code of deontology for 14C dating laboratories in order to enhance an ethical approach in this sensitive field facing the current challenges.
The University of Bern has set up the new Laboratory for the Analysis of Radiocarbon with AMS (LARA) equipped with an accelerator mass spectrometer (AMS) MICADAS (MIni CArbon Dating System) to continue its long history of 14C analysis based on conventional counting. The new laboratory is designated to provide routine 14C dating for archaeology, climate research, and other disciplines at the University of Bern and to develop new analytical systems coupled to the gas ion source for 14C analysis of specific compounds or compound classes with specific physical properties. Measurements of reference standards and wood samples dated by dendrochronology demonstrate the quality of the 14C analyses performed at the new laboratory.
A simple way to upgrade the Peking University 500kV NEC radiocarbon facility (CAMS) for 10Be measurements is presented. In a first phase, a silicon nitride foil as passive boron degrader was mounted in front of the electrostatic deflector near the focal plane of 10Be. The Si detector at the end of the beam line was replaced with a high-resolution ΔE-Eres gas ionization chamber. In addition, a Faraday cup for the measurement of 9Be1+ was installed. Tests with this arrangement showed promising results: a 10Be/9Be background level of 3.4 × 10–14 and an overall transmission for 10Be of 2.2% were obtained. Measurements of standards showed very good stability and reproducibility. In the next step, it is planned to add a second magnet to reduce the background and to partly compensate losses due to energy and angular straggling in the degrader foil by the energy and angular refocusing effect of a magnetic sector field. With this final arrangement, a performance with 10Be/9Be background levels at 10−15 and 10Be overall transmission of 6–7% can be expected. The design proposed in this paper has the advantage that the modifications can be realized in a rather inexpensive way and that the measurement performance for 14C will not be affected.
One crucial condition for the interpretation of ice-core records is the establishment of an accurate time-scale. This task is especially difficult for glacier sites in a complex topography such as the Alps, due to the often irregular deposition of fresh precipitation. In this work, dating techniques were applied to an Alpine ice core from upper Grenzgletscher, Monte Rosa massif (4200 m a.s.l.), representing about two-thirds of the total glacier thickness. They are based on (i) the radioactive decay of the isotope 210Pb, (ii) seasonally varying signals such as the concentrations of NH4+ and the isotopic ratio δ18O, and (iii) stratigraphic markers from Saharan dust falls, atmospheric nuclear weapon tests and the reactor accident in Chernobyl. From the combined application of these dating methods, a time period of 1937–94 covered by the ice core was derived. Dating uncertainty is <1 year for the period 1970–94 and ± 2 years for the period 1937–69. The observed thinning of the annual layers as a function of depth could be well described by a simple kinematic glacier flow model.
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