In 1991, a 14C ß-counting installation with four proportional CO2 gas counters was tested at the Modane underground laboratory, 1700 m below the summit of Pointe du Fréjus, reducing the muon flux to 4 muons per square meter and per day. With cosmic radiation attenuated by a factor of 2.106, the background level of the counters was reduced by 65 to 85% while its variability was reduced by a factor of 30–80 depending on the type of counter. The dating limit of these counters extends to well beyond 60,000 years.

We sampled individual growth rings from three ancient remnant bald cypress (Taxodium distichum) trees from a massive buried deposit at the mouth of the Altamaha River on the Georgia Coast to determine the best technique for radiocarbon (14C) dating pretreatment. The results of our comparison of traditional ABA pretreatment and holocellulose and α-cellulose fractions show no significant differences among the pretreatments (<1 sigma) thereby suggesting that ABA pretreatment will prove sufficient for the development of a high-resolution 14C tree-ring chronology based on these ancient bald cypresses which will indicate whether the U.S. Southeast is subject to a regional radiocarbon offset.

The second home-made single stage accelerator mass spectrometer (SSAMS) system dedicated to radiocarbon (14C) measurements was built after the first SSAMS system was moved to Guangxi Normal University. With some improvements to the second SSAMS system, the performance has been improved. With the conditions of total ion energy of 200KeV, ions charge states of 1+ and helium as stripper gas, 14C measurements with precision of 0.5% and a background level of 0.5 pMC were achieved. Details of the system and the experimental performance are given here.

Prehistoric cultures in Armenia are still poorly known; thus, accelerator mass spectrometry (AMS) radiocarbon dates are invaluable in constructing an accurate chronology. Bone samples have been collected from sites representing the Middle Paleolithic, Chalcolithic, and Early Bronze periods. Most of the bone samples are poorly preserved. We describe the separation technique for the extraction of both the bioapatite and collagen fractions. In many cases where the bone had very low organic material content, the collagen fractions yielded a younger age, although the ages of bioapatite fractions were found to be in good agreement with associated archaeological artifacts. In cases where bone was well preserved, both fractions exhibited ages in good agreement with the artifacts. The accuracy of 14C dating of bone material always depends on its degree of preservation, and each case should be carefully evaluated to determine which fraction is less contaminated in order to accurately date a burial event.

Huon pine is endemic to Tasmania. It has well-defined annual rings, may live for over 2000 years, and is particularly resistant to decay. Celery-top pine has similar characteristics and may live for 800 years. As part of a multi-disciplinary study of these trees and their habitat, a simple wood pretreatment method for isotope analysis is described. The solvent-acid-alkali-acid sequence yields a value of Δ14C = −16 ± 6‰ for AD 1941–45 Huon pine heartwood; Δ14C for extracts containing various proportions of post-AD 1955 carbon are also presented. Δ14C measurements on super-canopy and sub-canopy leaves from Celery-top pines are compared and used to place an upper limit of 10% on the amount of sub-canopy CO2 assimilated by sapling leaves, originating from decaying litter-mass. 14C ages from well-preserved logs illustrate the potential for a continuous Holocene chronology from 7400 years BP to the present. A 12,000-year-old Celery-top log has also been found.

Human remains from the (late) Middle Paleolithic remain rare. Improving our understanding of their spatio-temporal distribution is essential for obtaining insights into human evolution and the dynamics between Neanderthals and early Anatomically Modern Humans (AMHs). We present the single-amino-acid radiocarbon dating and ancient DNA results from the only Neanderthal skeletal remains known in Slovakia (Šal’a I and Šal’a II). As they were found without archaeological context and in secondary deposition, recontextualization is important. By employing the hydroxyproline radiocarbon dating method, we were able to successfully counteract contamination issues and circumvent problems caused by highly degraded collagen. By contrast, DNA analysis did not detect any endogenous DNA at the limits of our resolution. We conclude that the radiocarbon ages of >44,800 BP (OxA-X-2731-16) and >45,100 (OxA-X-2731-15) firmly place the two individuals in the Middle Paleolithic, and before the arrival of AMHs to the region. Furthermore, indirect evidence based on morphology and possibly related faunal remains suggest ages younger than 100 ka. This time frame coincides with a period in which Neanderthal populations were highly dispersed in Europe, yet in decline.

A significant reduction in cosmic-ray activity and backgrounds of the gas-filled proportional counters, as measured in a heavy iron shield, was observed when the Uppsala Conventional 14C Laboratory was moved in 1984. The new site was better shielded from cosmic rays because of additional concrete layers above the laboratory. A study that lasted over one year yielded a figure for the muon reduction. The backgrounds were reduced approximately to the extent expected from the soft-component contribution at the old Laboratory as judged from barometric-pressure dependence. After a few years, new electronics enforced, and enabled, the revision and improvement of the standard values for the activity and age calculations.

A careful analysis of the results for the counters has increased the accuracy of the small corrections needed to yield internal error-multiplication factors mostly between 1 and 1.5 for the background for short periods of up to 12 months, and <1.1 for the oxalic acid samples combined for the last few years of measurements in the laboratory. Similar results were obtained for two counters.

The method of determining the biobased carbon content in liquid fuel samples is standardized, but different laboratories use different protocols during sample preparation and perform the measurements using different machines. The accelerator mass spectrometry (AMS) laboratories use different combustion, preparation, and graphitization methods for the graphite production for the spectrometric measurements. As a result, the intercomparison between the laboratories is inevitable to prove precision and accuracy and to demonstrate that the results are comparable. In this study, we present the results of an intercomparison campaign involving three 14C accelerator mass spectrometry laboratories. Five samples were used in the measurement campaign, including two biocomponents (fatty acid methyl ester, hydrotreated vegetable oil), one fossil component (fossil diesel), and two blends (mixtures of fossil and biocomponent with 90–10% mixing ratio) in the laboratories of CEDAD (Italy), ETH (Switzerland), and INTERACT (Hungary). The results presented by the laboratories are comparable, and all three laboratories could determine the biobased carbon content of the samples within 1% relative uncertainty, which is acceptable in the scientific, economic, and industrial fields for biocomponent determination.

The effects of different measurement conditions and sample preparation in liquid scintillation counting of benzene for 14C dating were tested. The goal of this work was to find the highest figure of merit through the variation of scintillation cocktail to benzene ratio, and measurement windows. Measurements were performed on 5ml of benzene plus increasing quantities of scintillation cocktail (7g of PPO and 0.5g of Me2POPOP in 1L of scintillation-grade toluene). Spectra of both background and standard were obtained and the counting windows selected for the highest figure of merit (Q). The best condition was 5ml of benzene plus 0.75ml of scintillation cocktail. This spectrum is compared with that of 1) pure toluene-14C plus cocktail, and 2) pure benzene-14C in which the equivalent amount of PPO and Me2POPOP present in 0.75ml of cocktail was dissolved. A correlation between the increase of the amount of cocktail and the broadening of the spectrum was observed. The effect of wrapping the upper part of the counting vial with aluminum foil to reduce background was also tested. A drastic background increment was observed in the low energy range, for unwrapped vials; the standard spectrum showed a broadening and a lower counting efficiency which reduced the figure of merit.

Grey et al. (1969) have discussed the problems that arise when using the wet oxidation method for the preparation of CO2 from oxalic acid and suggest that, although offering an effective substitute, the dry combustion method also has problems.

The Inner Mongolian Plateau lies along the northern limit reached by the East Asian summer monsoon. This geographic setting makes it especially sensitive to environmental change and an excellent site for understanding Quaternary East Asian monsoon variability. In this study we present new results of hydrogen isotopic compositions of fatty acids extracted from sediments, which were used to construct Holocene paleoprecipitation (or moisture) changes in Northern China. The hydrogen isotopic composition (D/H ratio) of n-acids in the sedimentary sequence of the Duoerji peat, Inner Mongolia, was determined with gas chromatography and mass spectrometry. Changes in the precipitation from middle Inner Mongolia are recorded by the D/H ratio of n-C20, n-C22, n-C24, n-C26, n-C28 acids (δD). From 10–9 ka, the relatively high δD values indicate reduced precipitation in the Early Holocene. Subsequently, increased precipitation is reflected by reduced δD values from 9–5.5 ka. After 5.5 ka, gradually increasing δD values record an overall decrease in precipitation. The precipitation trends established for the Duoerji sequence are consistent with other major paleoclimate proxies in the East Asian monsoon region, especially with a distinct Holocene optimum of increased monsoonal activity from 9–5.5 ka. The δD resulting paleo-precipitation record clearly shows that the Holocene climate in Northern China is basically controlled by the insolation changes.

Glassy microspherules, typically 200μm or less in diameter, are well documented from a variety of terrestrial and extraterrestrial sources (Baker, 1959, p 192–198; Glass, 1969; Rost, 1969; McKay, Greenwood & Morrison, 1970; Mueller & Hinsch, 1970; Cross, 1971; O'Keefe, 1980). To these we would add the formation of microspherules of similar habit when wood charcoal is burned in a combustion bomb (Barker, Burleigh & Meeks, 1969; Burleigh, 1973, 1974; Switsur, 1973; Switsur et al, 1974) as a first step in the chemical synthesis of samples for 14C age measurement. The glassy material of these spherules originates from fusion at the high temperatures reached during the combustion, of traces of alkali-metal minerals in the charcoal and silica bodies (phytoliths) within its microstructure. Other materials commonly burned, such as bone collagen, do not yield microspherules. The age and source of the charcoal are immaterial, though different species (and perhaps other woody plant materials) may be more-or-less productive of spherules. Here we give a brief summary of the characteristics of these glassy microspherules, based on optical and scanning electron microscopy and energy-dispersive x-ray analysis.

This list contains the results of 14C determinations obtained at the laboratory in 1984. Our laboratory measures 14C activity in the form of methane with a proportional counter built by Heidelberg University and an electronic unit built by Berthold, Benelux Analytical Instruments. The sample counting time is 4000 minutes with printouts at 100 minute intervals. Sample error is reported as one standard deviation. δ13C for mortar is measured by the University of Lyon Laboratory, δ13C was not measured or estimated for other samples.

The floating dendrochronological sequence of pine wood from Józefowo, N. Poland was expected to cover the ∼660 BC radiocarbon (14C) excursion. The sequence was radiocarbon dated using the OxCal wiggle matching procedure and the IntCal20 calibration curve. 14C concentrations were measured in one-year α-cellulose samples from around 660 BC. The published data on the ∼660 BC 14C excursion from Grabie, Poland were used to absolute date the Józefowo chronology with 1-year accuracy. The results confirm the occurrence of a rapid increase in Δ14C in 664/663 BC and its potential to be used as a fixing point for floating dendrochronological sequences.

The archaeological site of Tlatoani at Tlayacapan is located in the Mexican Highlands, in the present-day state of Morelos. The site is an extant settlement located at the top of the Tepoztlan mountain range, and has been occupied since the Late Preclassic period (AD 150–500). At the height of its occupation in the Epiclassic and Early Postclassic periods (AD 600–1150), Tlayacapan was situated on the top of the hill. The radiocarbon investigations reported herein revealed some further distinct findings, although no clear absolute chronology was demonstrated. A dog skull was found inside the oldest foundation stage, and dated between cal AD 646 and 765, the middle of the Epiclassic period. Human remains found in the first grave belonged to three individuals. A male skeleton was dated to AD 1158–1227. Fragments of an incomplete skeleton of a child and an incomplete skeleton of a second male were placed on top of the first male skeleton and were dated in the range AD 1030–1156. A fourth skeleton found nearby in the second grave gave a similar date of AD 1164–1253. These burials were in accordance with the Middle America cosmovisional system, where bodies were buried beneath the household space. It is evident from the 14C dates of the skeletons that the burial sites beneath the household space had been reused by exhuming and reburying skeletons that had been previously buried there. A comparison of dates on fractions of collagen and bioapatite of the same bones was possible. Two of the samples were in good agreement between these fractions, whereas the other three samples are close but just outside the 2σ range.

The following list includes selected geologic and pollen dated samples measured since 1965. After moving to new laboratory quarters, we increased shielding to 470 g/cm2 on all sides and 660g/cm2 at the top. Background of our Houtermans-Oeschger-type counters filled with 700 mm Hg of acetylene is now: