The following list covers measurements of bomb-producedC14 in series of cereals and grassescollected on the northern hemisphere from 1956through 1966. Samples were measured in order todetermine the yearly addition of bomb producedC14 at a single locality, and to detectpossible geographic variations in the distributionand uptake of bomb-generated C14 interrestrial plant material during years with greatlyvarying additions of bomb C14.Measurements are given in the ∆ scale (Lamont VIII),i.e. per mil deviations from 0.95 times the activityof the NBS oxalic-acid standard (the naturalC14 level).

The standard procedure for measuring 14C at the Gif-sur-Yvette Tandetron AMS facility is described. A new sample manipulator and automated measurements are being used and have been operational for six months. Evidence of isotopic fractionation in the sputter ion source is provided. We take this into account by measuring the 13C/12C ratio of the sample in the accelerator.

The Fifth International Radiocarbon Comparison (VIRI) provided a suite of 5 bone samples with consensus ages ranging from 969 to 39,305 14C yr BP (Scott et al. 2010). These bones were used herein in a comparison of decalcification methods using either HCl or EDTA to produce collagen, and the results demonstrate age concordance between both preparation methods and the VIRI consensus values. Additional isotopic analyses of the collagen (δ13C, δ15N, and δ18O) illustrate the increasing sensitivity of carbon, nitrogen, and oxygen isotopes in assessing gelatin degradation.

An effective sealed tube combustion method was designed with an MnO2 oxidant for accelerator mass spectrometry radiocarbon (AMS 14C) measurements. Different types of materials (oxalic acid, cellulose, sucrose, wood, collagen, graphite, and humic acid) were used to test the method. A normal borosilicate glass tube was used instead of quartz and the combustion was done at 550ºC. The yield of the combustion is above 98% even in the case of the less combustible material such as graphite. The MnO2 reagent does not introduce detectable carbon contamination. The typical background is 0.29±0.20 pMC in the case of 200 µg carbon, measured as solid graphite target. With direct measurement of the CO2 by gas ion source AMS, the method is applicable up to 50 µg of carbon with an acceptable (~1 pMC) 14C background. A new type of tube cracker was developed for a quick chipless method of tube cracking and sample changing. In this way, the gas handling process takes only 5–6 min/sample.

This article is a critical review of published data from the earliest evidence of pressure knapped microblade technology from various regions in Northeast Asia (Siberia, Korea, China, Mongolia, Japan, Sakhalin, and Russian Far East), including discussions not only on published dates, but also on published artifacts (drawings and photos) relating to these assemblages. The issue concerning the geographical and chronological origin of microblade technology in Northeast Asia remains a widely debated concern, not only as new data emerge, but also due to researchers having different definitions of the term “microblade” and “microblade core”. In this case, by microblade technology, I refer to the systematic production of microblades using the pressure knapping technique. I therefore review the data in light of this defining feature and conclude that, based on the present state of research, pressure knapping microblade technology probably emerged in the Far East (China, Korea, or Japan) around 30,000–25,000 cal BP, in spite of most authors considering that microblade technology emerged in southern Siberia 40,000–35,000 years ago. In the discussion section, I argue about the potential role of obsidian in the emergence of pressure knapped microblade technology.

Four fen peat sequences in northern Finland were dated by the accelerator mass spectrometry (AMS) radiocarbon method in order to study past peatland dynamics and carbon accumulation patterns. Initially, plant macrofossils were used for dating. However, the dates were severely disordered, with marked inversions in all sequences. In one 140-cm peat core, for example, all ages fell within a ∼1000-yr time window. Following these unreliable results, a few bulk peat samples were dated to help assess if any of the plant macrofossil-derived dates were reliable. Bulk dates did not help to solve the problem. This study evaluates the possible sources of error but is unable to single out one clear cause. It is probable that many factors related to the fen environment, such as flooding and root intrusion, may have contributed to the errors. Peat plant macrofossils and bulk peat samples are considered to be reliable dating materials, but the examples given herein highlight the difficulties that can be associated with AMS dating of peat samples.

Fundamental to the field of radiocarbon dating is not only the establishment of the temporal record of the calendar age-radiocarbon age offsets but also the development of an understanding of their cause. Although part of the decline in the magnitude of this offset over the past 40,000 can be explained by a drop in 14C production rate associated with a progressive increase in the strength of the Earth's magnetic shielding, it is clear that changes in the distribution of 14C among the Earth's active carbon reservoirs are also required. In particular, the steep 15% decline in the 14C to C ratio in atmospheric CO2 and surface ocean ΣCO2, which occurred in a 3 kyr-duration interval marking the onset of the last deglaciation, appears to require that a very large amount (at least 5000 gigatons) of 14C-deficient carbon was transferred to or within the ocean during this time interval. As no chemical or stable isotope anomaly associated with this injection appears in either the marine sediment or polar ice records, this injection must involve a transfer within the ocean (i.e. a mixing of 2 ocean reservoirs, one depleted in 14C and the other enriched in 14C). Although evidence for the existence of a salt-stabilized glacial-age abyssal ocean reservoir exists, a search based on benthic-planktic age differences and 13C measurements appears to place a limit on its size well below that required to account for the steep 14C decline.

Radiocarbon dating was first applied to historic lime mortars during the 1960s. However, despite the relative simplicity of the technique in principle, a number of subsequent studies have highlighted important aspects that should be considered. One of the most significant of these challenges arises from sample contamination by carbonaceous substances such as incompletely burnt limestone and aggregates of fossil origin containing “dead” 14C. More recent studies have shown that in the majority of old lime-based mixtures the contamination problem can be avoided through selection of pure lime lumps. These particular types of lumps are believed to originate from areas where the lime is incompletely mixed with the aggregate. It has been demonstrated that even a single lime lump can provide sufficient material for a 14C date of the mortar from which the lump was taken (Pesce et al. 2009). This paper describes the practical challenges associated with location, extraction, and preparation of 4 lime lumps extracted from 2 new sites for 14C dating. These include distinguishing the lime lumps from other lumps present in the matrix and the removal of material surrounding the lime lump. The coherence of 14C dating with other archaeological information on the chronology of historic sites is highlighted through case studies.

Radiocarbon dating of plant remains is often difficult due to the complete dissolution of the samples in the alkaline step of the ABA pretreatment. At the VERA laboratory, this problem was encountered frequently when numerous Bronze and Early Iron Age samples from the eastern Mediterranean were dated in the course of the special research program SCIEM2000 and in other collaborations with archaeologists focused on that area and time period. For these samples, only a 14C age determination of the humic acid fraction was possible. Humic acids from archaeological samples are always assessed as a second-choice material for 14C dating. It is assumed that the 14C ages may be affected by the presence of humic acids originating from other (younger) organic material, e.g. from soil horizons located above a sample. Therefore, when humic acids are dated a verification of the dates is crucial. To address this basic requirement, we started some time ago to date both fractions of charred seeds, wood, and charcoal samples whenever available, i.e. the residue after the ABA treatment and the humic acids extracted from the samples in the alkaline step. The results of this comparison showed that for the investigated eastern Mediterranean archaeological sites, 50 (out of 52) humic acid dates were in agreement with the 14C dates of the respective ABA-treated samples. Statistical analysis of the age differences leads to the conclusion that the extracted humic acids originated from the samples themselves or from contemporaneous material and were not appreciably contaminated by extraneous material of different age.

Two radiocarbon (14C) excursions are caused by an increase of incoming cosmic rays on a short time scale found in the Late Holocene (AD 774–775 and AD 993–994), which are widely explained as due to extreme solar proton events (SPE). In addition, a larger event has also been reported at 5480 BC (Miyake et al. 2017a), which is attributed to a special mode of a grand solar minimum, as well as another at 660 BC (Park et al. 2017). Clearly, other events must exist, but could have different causes. In order to detect more such possible events, we have identified periods when the 14C increase rate is rapid and large in the international radiocarbon calibration (IntCal) data (Reimer et al. 2013). In this paper, we follow on from previous studies and identify a possible excursion starting at 814–813 BC, which may be connected to the beginning of a grand solar minimum associated with the beginning of the Hallstatt period, which is characterized by relatively constant 14C ages in the period from 800–400 BC. We compare results of annual 14C measurements from tree rings of sequoia (California) and cedar (Japan), and compare these results to other identified excursions, as well as geomagnetic data. We note that the structure of the increase from 813 BC is similar to the increase at 5480 BC, suggesting a related origin. We also assess whether there are different kinds of events that may be observed and may be consistent with different types of solar phenomena, or other explanations.

The present list comprises only research projects undertaken by the laboratory on the validity of radiocarbon dating of soil, shell, coral and very old samples, all in presence of suspected contamination. All measurements were performed on a Beckman LS-200 liquid scintillation spectrometer (Radiocarbon, 1968, v. 10, p. 179-199). The chemical treatment of samples is given within the text of each section.

Radiocarbon determinations, employing both decay and direct counting, were obtained on various organic fractions of four human skeletal samples previously assigned ages ranging from 28,000 to 70,000 years on the basis of their D/L aspartic acid racemization values. In all four cases, the 14C values require an order of magnitude reduction in age.

This list contains dates for Latin America which have mainly been measured during the past few years. The results are grouped into three categories: geologic, archaeologic, and geophysical, and arranged according to the country of provenance, passing roughly from N to S. Most of the geologic samples are connected with palynologic studies. In cases where the influence of man is apparent in the pollen diagrams, this is explicitly mentioned. Descriptions and comments are based on information provided by the collectors or submitters and on the publications referred to under each sample or series. For the archaeologic section reference has also been made to the general works of Meggers and Evans (1963), Jennings and Norbeck (1964), and Willey (1966).

Radiocarbon dating of mollusks and barnacles from fossil shoreline deposits in the Persian Gulf and on the coast of Iranian Makran is being used to assess the extent and rate of recent crustal deformation in the area. Samples are selected with the help of x-ray diffraction and of light and scanning electron microscopy; whenever possible, two or more ages are determined for each locality on monospecific samples. Age/height values have been used to compute local uplift rates by allowing for sea-level fluctuations, but eustatic controversy can be avoided by limiting the analysis to fault chronology and to relative vertical movements between dated sections. Short counting times on large, carefully pretreated samples would supply the numerous, cheap, low-resolution ages required to follow up the preliminary results obtained by the survey.

This study used high-precision radiocarbon bomb-pulse dating of selected wood rings to provide an independent validation of the tree growth periodicity of Pseudolmedia rigida (Klotzsch & H. Karst) Cuatrec. from the Moraceae family, collected in the Madidi National Park in Bolivia. 14C content was measured by accelerator mass spectrometry (AMS) in 10 samples from a single tree covering over 70 yr from 1939 to 2011. These preliminary calendar dates were determined by dendrochronological techniques and were also used to select the samples for 14C AMS. In order to validate these preliminary dates using the established Southern Hemisphere (SH) 14C atmospheric concentration data set, the targeted rings were selected to be formed during periods before and after the 14C bomb spike nuclear tests (i.e. 1950s–1960s). The excellent agreement of the dendrochronological dates and the 14C signatures in tree rings associated with the same dates provided by the bomb-pulse 14C atmospheric values for the SH (SHCal zone 1–2) confirms the annual periodicity of the observed growth layers, and thus the high potential of this species for tree-ring analysis. The lack of discrepancies between both data sets also suggests that there are no significant latitudinal differences between the 14C SHCal zone 1–2 curve and the 14C values obtained from the selected tree rings at this geographic location (14°33′S, 68°49′W) in South America. The annual resolution of P. rigida tree rings opens the possibility of broader applications of dendrochronological analysis for ecological and paleoclimatic studies in the Bolivian tropics, as well as the possibility of using wood samples from some tree species from this region to improve the quality of the bomb-pulse 14C SHCal curve at this latitude.

Two radiocarbon counting systems have been established in the Chemistry Department, University of Glasgow, since late 1967.

The counting gas is methane, at pressures up to 10 atm, and 2 alternative procedures are followed for methane production, (a) high pressure synthesis in a stainless steel 4.5 1 reactor and (b) low pressure synthesis in an all glass flow-reactor. Both systems employ 0.5% ruthenium on alumina pellets as catalyst (Engelhard Industries Ltd.). Early samples synthesized with Air Products' hydrogen showed evidence of tritium contamination. This gas supply was later replaced with tritium-free hydrogen supplied by Messrs. Griesheim, Düsseldorf, Germany. Both detectors used for routine measurements are 0.5 1 internal gas counters supplied by Beckman Instruments Inc., California. The detectors are surrounded by a concentric-wall multiple anode anticoincidence counter. The entire counter assembly is encased within a 4-in.-thick lead shield manufactured from aged lead by J. Girdler and Co., London. Counter electronics, anticoincidence system and power supply are of Beckman design (Sharp and Ellis, 1965).

This work summarizes the methodical capabilities, improvements, and new developments in the radiocarbon laboratory of the accelerator mass spectrometry (AMS) facility at the University of Cologne, Germany, which was established in 2010. During the past years, the laboratory has specialized in the analysis of small and gaseous samples. We thus, recently installed a second ion source dedicated for radiocarbon (14C) analysis of CO2 samples at our 6 MV Tandetron AMS from High Voltage Engineering Europe B.V. that is coupled with the gas injection system from Ionplus and an EuroVector EA 3000 elemental analyzer. This work summarizes all pretreatment methods and analytical facilities established in our laboratory during the last years including 14C analysis of individual organic compounds and of CO2 trapped on molecular sieves. We also report different blank values including our long-term blank since 2011, which is for normal-sized, solid samples (650–1000 µg C) 0.0012 ± 0.0004 F14C (54,305 ± 2581 yr BP, n = 484). The precision obtained for modern samples measured as graphite is 0.5% and for gaseous samples injected with the GIS ≤2%.

Radiocarbon dating with accelerators requires the manufacture of suitable carbon targets. Carbon yield and 13C fractionation were investigated for the simple and direct pyrolysis of wood and cellulose to charcoal. Under continuous vacuum removal of evolved volatiles, carbon yields of 35 to 40% and δ13C fractionation of −2.5‰ were observed in the pyrolysis of wood to charcoal, whereas yields of 30% and fractionation of −0.8‰ were obtained in the pyrolysis of cellulose to charcoal. Yield and fractionation leveled off at temperatures above 300°C. Yields and fractionations were also measured for pyrolysis of wood and cellulose in a continously-flowing argon atmosphere. Yields were higher and fractionations smaller than for the corresponding vacuum cases. For cellulose sealed in evacuated glass tubes and pyrolized at 550 to 600°C, carbon yields greater than 60% and fractionation of about −0.5‰ were observed. Yields increased and fractionation tended to decrease as the ratio of tube volume/mass of cellulose decreased, ie, as the pressure increased. Reheating of this charcoal under continuous vacuum pumping revealed no loss of mass and no alteration of carbon isotopic composition. Fractionation measurements were additionally performed on wood and the charcoal produced from burning in a fireplace, conditions approximating the “natural“ production of charcoal. Despite the large potential fractionation suggested in the wood pyrolysis experiments, charcoal produced in the fireplace showed very small or no fractionation.

The distribution of 14C concentrations in the dissolved inorganic carbon in the surface waters of the Pacific Ocean is shown to have a primarily latitudinal pattern with Δ14C maxima at mid-latitudes in both hemispheres and a minimum at the equator. Oceanographic causes of this phenomenon are discussed.

The eastern Adriatic is a key area for understanding the mechanisms and effects of the spread of agriculture. This article presents an accelerator mass spectrometry (AMS) radiocarbon chronology for the introduction and subsequent development of farming villages on the eastern shore of the Adriatic (∼6000–1700 cal BC) and evaluates this in comparison with the established pottery chronology based on stylistic data from Pokrovnik (Drniš) on the Dalmatian coast of Croatia. Models for the spread of agriculture rely heavily on changing pottery styles to define cultural groups and trace geographic relationships. Based on AMS 14C dates presented here, Impressed Wares first appear in central Dalmatia by 6000 cal BC and persist until 5300 cal BC, well into what is generally termed the Middle Neolithic. Similarly, a typical Middle Neolithic ware, figulina, appeared earlier than anticipated. These findings stand in contrast to cave and rockshelter assemblages in the eastern Adriatic, but mirror assemblages from farming villages on the Italian Adriatic coast. This study argues that the similarities in ceramic assemblage composition and change through time may have less to do with direct contacts between areas, but more with the nature of ceramic production and consumption at village sites in general. These data shed light on the limitations of regional ceramic chronologies in the eastern Adriatic and highlight the necessity for systematic expansion of 14C chronologies to address the social, economic, and ecological relevance of early farming in the Adriatic for the spread of agriculture in Europe and the Mediterranean.