Results obtained from a liquid scintillation counter using BGO (Bi4Ge3012) tubes have produced more precise radiocarbon dates in our laboratory. Duplicate analyses confirm the electronic stability of the counter with a background of 0.1 cpm. Our 14C dates agree well with those from another laboratory (Paris 6-LOCEAN). Most of the 14C dates in this study were obtained on samples taken from different archaeological sites. Calibration of the various dates with the appropriate software (CALIB 5.0 in our case) allows better interpretation of the results and their importance in this understudied region. In this paper, we investigate the performance of the counter by analyzing samples from archaeological and marine sites in Senegal and Mauritania, and report the results in our first laboratory date list.

During the 1989–1994 renovation of the Zagreb Town Museum, it became obvious that the area was inhabited in prehistoric times. We 14C dated 40 samples to determine various settlement periods. The ages of the samples span a much longer time than expected, from the Early Iron Age (Hallstatt period) to the 19th century ad. 14C dates on charcoal samples placed the remains of dwelling pits in the Hallstatt period, 8th to 4th century bc. A late La Tène settlement dated between the 4th century bc and the 2nd century ad. Medieval fortifications were identified in the western part of the complex, consisting of a well-preserved wooden structure used for construction of the royal castrum. 14C measurements on wooden planks and posts date the construction of the fortification between the 13th and 15th centuries ad and branches, beams, and tools found below the basement of the Convent of St. Clare span the 16th to the 19th century ad.

The Brazil Nut tree (Bertholletia excelsa, Lecythidaceae) is a species of considerable historical, economic and ecological importance in South America. Radiocarbon dating indicates some individuals can live from hundreds to more than 1000 years, which means they have the potential to reconstruct deep time growth patterns and their relationship to anthropogenic management or climate change from pre-colonial to present times. However, age estimates vary considerably amongst trees dated with different methods (i.e. tree-ring analysis, radiocarbon-dating, and repeated diameter measurements). Here we analyze living Brazil Nut trees growing in four distinct regions across the Brazilian Amazon using two dating methods: tree-ring counting and radiocarbon dating. Our results show that the congruence between the two methods varies amongst regions, and the highest congruence is found at the site of Tefé, Amazonas. This region features archaeological sites with anthropogenic Terra Preta soils, and is known for its long-term human forest management. This management likely enhanced light and nutrient availability, which possibly enabled the trees to grow at higher rates and form annual rings. Our findings highlight the need for better understanding of the growth of Brazil Nut trees for ecological research, but also the potential of dendrochronology for exploring climate change and human-forest interactions in the Amazon Basin.

From 1966 to 1979, the University of Missouri, the University of Arizona, and the Illinois State Museum conducted extensive interdisciplinary investigations of Late Pleistocene peat deposits associated with springs, some extinct, in the Pomme de Terre River Valley of the Ozark Highland, Missouri (fig 1). Most of the sites are now beneath the waters of the Harry S Truman reservoir. Archaeologic investigations in the area produced a remarkably long sequence of cultural change and development during the Holocene but produced no evidence of human presence in the area prior to 11,000 years ago despite diligent excavation of favorable bone-bearing deposits.

Since radiocarbon accelerator mass spectrometry (14C AMS) is considered a high-precision technique, reassessment of the measurement uncertainty has been a topic of interest. Scientists from analytical and metrological fields have developed the top-down and bottom-up measurement of uncertainty approaches. The 14C quoted error should approximate the uncertainty of long-term repetitions of the top-down approach in order to be realistic. The novelty of this paper is that the uncertainty of both approaches were approximated to each other. Furthermore, we apportioned the graphitization, instrumentation, and bias components in order to additively expand the quoted error. Our results are comparable to error multipliers and to long-term repeatability studies reported by other laboratories. Our laboratory was established in late 2012 with N2 as stripper gas and 7 years later, we changed to helium stripper. Thus, we were able to compare both gases, and demonstrate that helium is a better stripper gas. In absolute F14C units, the ranges of graphitization+bias combined uncertainties were (0.7 to 4.1) × 10–3 for N2 and (0.7–3.0) × 10–3 for He depending on the standard 14C content. The error multiplier for He defined as the expanded uncertainty over quoted error, in average, was 1.7; while without the bias, the multiplier was 1.3.

The following is a partial list of samples of archaeological interest processed between February 1981 and October 1985 at the Illinois State Geological Survey (ISGS) Radiocarbon Dating Laboratory. The list contains samples from west-central Illinois that were related to projects conducted by current or former researchers at the Center for American Archeology (CAA) (formerly Foundation for Illinois Archaeology) and Northwestern University, Department of Anthropology, or, as noted, by colleagues from other institutions. Although some of the samples reported here came from non-cultural contexts and are primarily of geological significance, all were from or related to archaeological investigations.

The following results represent measurements carried out since our first date list was prepared. Nearly all the dates given were obtained by using two proportional counters. The pretreatment of the samples and the production of pure CO2 followed the method described in Finland I.

The earliest years of photography were full of experimentation and innovation; many photographers from this era carefully documented their experimental procedures. Consequently, it is possible to reproduce historically accurate photographs and negatives today. One of the oldest forms of photographic technology is the waxed paper negative, popular during the mid-19th century. It consists of a photosensitive sheet of writing paper coated with a layer of wax to render it transparent. Modern waxed paper negatives made using 19th century paper can potentially pass for historically significant 19th century negatives. This poses problems to museums and others interested in studying or collecting authentic 19th century photographic images. We have developed methods for separating the organic components of waxed paper negatives and measuring their radiocarbon content as a means of distinguishing between modern and historic waxed paper negatives. By detecting the presence or lack of bomb carbon in a given negative, this process can act as a tool for authentication. We have mainly focused on the extraction and 14C measurement of the wax component, reasoning that modern photographers might have easy access to 19th century paper, but would less likely use 19th century beeswax.

Fungal hyphae associated with tree roots extending into the surrounding substrate are suspected to have to contaminated buried plant material with recent carbon in two examples and to have resulted in erroneously young radiocarbon ages. This problem might be overcome by choosing sampling sites far from trees or by analyzing the lignin component of samples, although the latter is presently difficult.

This paper describes the results of Bayesian modeling of radiocarbon dates from Early Bronze Age contexts in Southern Mesopotamia, modern-day southern Iraq. The model uses 14C dates available in the literature, employing archaeological and textual information to correlate contexts from a number of important Mesopotamian sites. The insufficient number of dates makes it impossible to precisely define the chronology of the period in question; however, the analysis allows for observing patterns of cultural change otherwise invisible in archaeological and textual records. Firstly, it is suggested that there was a hiatus of at least a century between the latest protocuneiform texts and the earliest historical writing. Furthermore, the results seem to argue against a steady, gradual evolution of literate civilizations, indicating a more complex and varied process of development.

The chronology of long Upper Pleistocene loess sequences in Eurasia is based on combined pedostratigraphy and radiocarbon dating of high-quality charcoal. The accuracy of such a chronology depends on the reproducibility and precision of the 14C dates. However, certain dates may show discrepancies with regard to their chronostratigraphic context based on series of coherent dates. In order to evaluate the consistency and variation in the 14C dates obtained from small charcoal pieces, this question was tested on a set of spruce wood remains with well-preserved tree rings found in the Middle Pleniglacial loess-loam sequence of Kurtak (central Siberia). Tree-ring analysis of five fairly large wood pieces from three successive layers, dated to about 30.0, 30.8, and 32.2–32.5 ka BP previously, was done by continuous sampling of 90–150 rings on each wood piece. This enabled direct comparison of the succession of tree rings with the 14C dates. A total of 133 dates was obtained for the five wood pieces. The results show fluctuations in the 14C dates within a time range between 1000 and 2000 yr. Four possible causes for such variation will be discussed herein: (1) internal variability of the AMS dating method; (2) outliers; (3) variations in the 14C background; and (4) external factors such as past atmospheric 14C variations.

Little is known about the potential complications that may arise from the use of coastal foraminifera for radiocarbon (14C) dating. The aim of this study is to report the fortuitous finding of 14C-dated Haynesina germanica individuals picked from two sediment cores (Pertuis Charentais, France), which appeared 2500–2000 years older than their expected age of deposition. Stratigraphical and micropaleontogical evidence have ruled out the possible effect of reworking of calcareous tests from previous strata. Similar anomalous 14C ages were obtained on abundant lignocellulose debris recovered from the cores, which are supplied by rivers flowing into the study area. Given that H. germanica is an infaunal species, we hypothesize that in-situ living individuals acquired the 14C-depleted isotopic signature of lignocellulose debris within the sediment prior to definitive burial, following an unexplored pathway of carbon transfer between the two compartments. Based on the literature, we propose a plausible explanation, which involves bacterial communities living in the study area. This putative role of bacteria may have considerable importance for past and future studies of Holocene environmental changes in coastal environments. Further work is now needed to explore this hypothesis with more robust, direct evidence based on comprehensive geochemical, geochronological and microbiological studies.

Areas affected by routine radiocarbon (14C) discharges from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) and accidental releases in March 2011 were investigated by analysis of cores from Japanese cypress and cedar trees growing at sites 9 and 24 km northwest of the plant. 14C concentrations in tree rings from 2008–2014 (before and after the accident) were determined by accelerator mass spectrometry, with 14C activities in the range 231–256 Bq kg−1 C. Activities during the period 2012–2014, after FDNPP shutdown, represent background levels, while the significantly higher levels recorded during 2008–2010, before the accident, indicate uptake of 14C from routine FDNPP operations. The mean excess 14C activity for the pre-accident period at the sites 9 and 24 km northwest of the plant were 21 and 12 Bq kg−1 C, respectively, indicating that the area of influence during routine FDNPP operations extended at least 24 km northwest. The mean excess tree-ring 14C activities in 2011 were 10 and 5.8 Bq kg−1 C at 9 and 24 km northwest, respectively, documenting possible impact of the FDNPP accident on 14C levels in trees.

Air pollution in Mexico City, which has more than 22 million inhabitants, continues to be one of the main environmental issues. Aerosol samples (PM10) collected in Mexico City and the city of Cuernavaca (a clean reference site) have been characterized using different techniques. This multifaceted approach addresses the source apportionment of the carbonaceous matter in PM10, as well as the airborne elements and ions. Accelerator mass spectrometry (AMS) radiocarbon analysis of total carbon, X-ray fluorescence (XRF), and ion chromatography were performed on aerosols collected at three sites in Mexico City and one site in Cuernavaca, during 2 months of the cold-dry season (November–December) in 2012. New results obtained for Mexico City are compared with previous reports. Average levels of PM10 were higher in Mexico City sites (43.3–60.8 μg/m3) than in Cuernavaca (32.2 μg/m3). According to the material balance, PM10 collected in Mexico City had a lower contribution of crustal material (31.2–36.8%) than Cuernavaca (46.9%). Average contributions of particulate carbonaceous matter to PM10 were similar in both cities, but much higher contributions of mineral salts, trace elements, and ions were observed in Mexico City in comparison to Cuernavaca. Total organic carbon (OC) and elemental carbon (EC) contents were higher in aerosols from Mexico City than those from Cuernavaca. The temporal variation results showed that within all locations studied the OC concentration was high compared to the EC. Results from a theoretical calculation of fossil carbon (FC) and biogenic carbon (BC) concentrations showed that FC and BC levels depend on the site: at Mexico City sites, FC was equal or higher than BC. At Cuernavaca, BC was always higher than FC.

The following list comprises measurements made since those reported in NPL IV.

No changes have been made in measurement technique or in the method of calculating results

The remains of a wooden construction, recovered in the 1970s at the northwest sector of the walls of the ancient city of Amphipolis (northern Greece), have been recognized as foundation remains of a wooden bridge described by Thucydides in his description of the events that took place at Amphipolis in 424–422 BC, during the Peloponnesian War. Frequent repairs in the Roman, Byzantine, and even Ottoman periods are very probable. In the last 10 yr, conservation has been done to enhance this unique monument. This work involves systematic investigation with radiocarbon dating of all the verified or suspected phases of this wooden bridge. The dating results reveal the beginning of construction most probably in the Archaic period and confirm beyond a doubt that the major construction phase took place in Classical times. Successive phases, related to repairs rather than to major reconstructions, have been detected during the Hellenistic, Roman, Early Christian, and Byzantine periods as well as the Ottoman era. The combined archaeometric and archaeological evidence leads to the remarkable conclusion that this bridge was functioning for about 2500 yr.

The following radiocarbon measurements are a partial list of geologic samples from S Florida dated during the summer of 1975. The technique used is liquid scintillation counting of wholly synthesized benzene as indicated in R, v 16, p 402-408 and R, v 18, p 210-220. Dates are calculated using a 14C half-life of 5568 yr and errors are reported as one standard deviation. Before conversion, shell material was etched with HCl to remove all soft or powdery material. All wood and peat samples were treated with NaOH.

Thirty-one samples of 5 tree rings from a single oak trunk with 300 tree rings were measured with improved precision to study natural 14C variations in the period from ca 9750 – 10,050 cal bp. Negative correlation was found between Δ 14C values and tree-ring indices. The pattern of 14C changes in the studied interval closely resembles the changes observed in several periodically spanned intervals within the limits of high-precision calibration data sets.