Measurements have continued with the same proportional counter system, the same procedure in sample pretreatment, methane preparation and measurement, and the same age calculation using a half-life of 5568 ± 30 yr as described previously (R., 1970, v. 12, p. 298–318).

The release and the speciation of carbon species from irradiated JRQ carbon steel samples, representative of the reactor pressure vessel of Belgian nuclear power plants, were studied in a saturated portlandite aqueous solution, relevant for the Belgian Supercontainer design, as perceived for the geological disposal of high-level nuclear waste. To achieve this, we performed simple immersion and potentiostatic corrosion tests. In addition, the corrosion rate (which determines the 14C release) was estimated by measuring the release of 60Co. Gas chromatography showed that during the static corrosion test, the carbonaceous species methane, carbon dioxide, ethene, and ethane were produced. Under the hypothesis that all the carbon released from the JRQ steel was transformed into carbon-base gaseous compounds, this corresponds to a corrosion rate of approximately 100 nm/yr, which is in good agreement with literature data.

It has long been assumed that radiocarbon (Δ14C) content of dissolved inorganic carbon (DIC) is equal to that of particulate organic carbon (POC) in surface seawater; however, little research has been conducted to explicitly test this assumption. Here, we report Δ14C measurements of surface POC samples and compare them with contemporaneous DIC Δ14C measurements from the northeast Pacific Ocean (Hwang et al. 2004; Druffel et al. 2010). Samples were collected from surface waters at Station M off California between 1995 and 2004. The POC Δ14C values decreased 3.2% per year from 1995 to 2004, similar to the decline observed in the DIC Δ14C values during the same period. Overall, our results show no statistical difference between POC and DIC Δ14C—consistent with the assumption that DIC and POC Δ14C values can generally be considered equivalent. However, significant variability was observed for POC Δ14C values during several fall/summer events, where POC Δ14C signatures were lower than DIC Δ14C values. An evaluation of 2 sample pretreatments also suggests that non-homogenized POC samples deviated less from average POC Δ14C values and more closely matched the DIC Δ14C average for the time series. The presence of seasonal POC/DIC Δ14C disagreements, combined with sample processing effects, suggest that infrequent contributions of allochthonous, older carbon may have originated from deeper in the water column, especially during periods when upwelling in this area was prominent.

Direct accelerator mass spectrometry (AMS) dating is crucial for a correct integration of plant remains in the (pre)history of crops, particularly for those that do not belong to the Neolithic package and are known to arrive in Europe much later. This paper reviews one of the earliest records of rye from Romania. The grains were discovered in the tell settlement of Cunești, which belongs to the Gumelnița communities (ca. 4600–3900 BC). In 1954, due to Danube flooding, a large portion of the south part of the tell collapsed, and between the burnt dwelling visible in the resulting profile, a large number of sherds from three typical Gumelnița pots were identified. According to the excavation’s author, rye grains were found in association with those sherds, and it was assumed that a batch was stored in these Eneolithic vessels. Consequently, the rye was published as belonging to the Gumelnița period. Our reanalysis led to two radiocarbon (14C) dates, from two different laboratories, which indicate that the Cunești rye is not prehistoric but dates to the medieval period. To correct this error concerning this rye batch and the implications for European archaeology, we decided to republish these grains in an updated chronological framework. In addition, we performed stable isotope analyses on the charred grains, confirming they were cultivated on dry land, as well as a 3D morphometric investigation. Our research brings new and original data on rye cultures from the medieval period in southeastern Europe.

Results of the International Collaborative Study show an unexpectedly large scatter of individual dates as well as systematic biases. Very high values of linear correlation coefficients are observed for all results of Stage 2 and for benzene samples of Stage 1. We observed moderate correlations for carbonate samples and the lowest for natural samples of wood and peat of Stage 3. The correlation is practically negligible among results obtained in different stages. The probable reasons for such effects are seen in medium-term changes in the calibration of the counting systems.

This list contains the results of 14C age determinations obtained at the laboratory in 1981–1982. Samples are analyzed in three new proportional counters which are described in R, 1980, v 22, p 442. Our installation differs from that of Heidelberg in that our filling gas is methane.

Concentrations of 10Be in ice cores and marine sediments exhibit 2 peaks with significant enhancements at 35,000 and 60,000 BP. This radioisotope is produced in the upper atmosphere by spallation of cosmic-ray protons and secondary neutrons on atmospheric nitrogen and oxygen. Previously suggested explanations for the increases include geomagnetic field reversals, a decrease in solar activity, and a supernova explosion. We propose an alternative explanation which involves a change in the galactic environment of the solar system. The structure of the heliosphere is investigated for a period when the Sun enters a cold, dense, unmagnetized interstellar cloud. Under these conditions, the heliosphere contracts to 25% its present size, significantly affecting galactic cosmic ray modulation and increasing anomalous cosmic ray fluxes. A tenfold increase in anomalous cosmic ray flux and a twofold increase in galactic cosmic ray intensity at Earth are possible in this high-density case if heliosheath modulation is reduced. We show that this increase in galactic cosmic ray intensity could be responsible for the peaks in 10Be records.

Samples in this paper are a continuation of the Florida geologic samples, reported earlier (R, 1978, v 20, p 436–440). Each specimen analyzed in this list was a carbonate shell. All dates are from single shells as opposed to means of multiple shell samples.

The absolute dating of mortar by accelerator mass spectrometry (AMS) has been the subject of renewed interest for several years. International intercomparison campaigns, called MODIS (MOrtar Dating Intercomparison Study), have been carried out. The first MODIS-1 campaign highlighted limitations in mortar dating, due to the similarity between the primary material to be dated (binder) and the contaminant (exogenous CaCO3). Methods have since emerged to overcome this problem and the need for a good preliminary characterization has been proven. The Laboratoire de Mesure du Carbone 14 (LMC14) took part in the second intercomparison campaign, MODIS2, by applying thermal decomposition increments to distinguish the carbonated binder, the organic matter contaminants (late in formation pyrogenic carbonate, LDH) and limestone. The LMC14 results on MODIS2 are quite conclusive on “pure” re-carbonated lime mortar binders containing little contaminant geological limestone but show their weaknesses for mortars heavily contaminated in Dolomites, which are difficult to discern from the binder. Recommendations for users of radiocarbon (14C) dating on mortar-based materials are made in the conclusion.

Charcoal from layer of buried soil from old brick works in Mende, Hungary (47° 30′ N Lat, 19° 30′ E Long) [unconfirmed, D.B.S.]. Deposits are humic loess loams, containing bits of charcoal. Sample at depth ca. 6.5 m. This cross section is one of classical loess excavations in Hungary. Sample coll. 1964, by M. Pechi [Pees] and D. Khan [Hahn].

This paper reports the first chronological assessment of the Christian catacombs of Rome by radiocarbon dating. The organic materials dated were found in a set of burial rooms in the so-called Liberian region of the catacombs of St. Callixtus on the Appian Way. 14C dating of small samples by accelerator mass spectrometry (AMS) represents a major advance over traditional archaeological dating methods used in catacomb archaeology; however, AMS 14C dating raises questions about sample reliability and chronological evaluation. We briefly explore these questions.

Radiocarbon (14C) measurements undertaken by the NERC Radiocarbon Laboratory using accelerator mass spectrometry (AMS) are now freely available on a new online database. The data presented covers measurement of the wide range of sample types that are processed for research projects in the fields of Earth and environmental science, supported by the United Kingdom’s Natural Environment Research Council. Sample types within the database include organic remains, soils, sediments, carbonates, dissolved organic and inorganic carbon, and carbon dioxide. Currently, the database contains 14C data for over 2400 individual samples that were measured and reported between 2005 and 2013, but it is envisaged that this will expand considerably as more data are made available. Contextual information such as sampling location and associated publications are provided where available, and searches can be performed on sample location, sample type, project number, and publication code. This new database compliments an existing, publicly available database of measurements performed using radiometric methods by the laboratory which has recently been expanded to present over 2000 measurements. It is hoped that this archive will prove useful to workers in the community who would benefit from greater availability of measurements for particular locations or sample types, and for the purposes of performing meta-analyses, and/or synthesis of larger datasets.

We present a new method for creating an OxCal Bayesian model that bypasses the complex task of writing OxCal code. Our methodology employs the recent ChronoLog software as a graphical front-end for generating OxCal scripts. This approach enables archaeologists to create complex Bayesian models—including termini post and ante quem, duration bounds and synchronisms—with the help of a user-friendly interface. The target audience can be divided into beginners, who might struggle to create chronological models using OxCal directly, and experienced OxCal users, who should find that ChronoLog saves time when coding complex models. Three case-studies from recent publications are presented.

Food production is one of the most significant achievements in Andean history. The domestication of plants and animals presented an enormous challenge, relating to changing technologies, settlement patterns, and social organization. This paper aims to assess Atacama Desert population dynamics and their relationship to the domestication of plants and animals through chronological modeling using kernel density estimation on radiocarbon (14C) dates, assuming that a higher 14C probability density is related to more intense human occupation. The analysis is based on a 14C dataset comprising 1003 14C dates (between 11,000 and 150 BP) from 243 archaeological sites in the Arica and Tarapacá regions of northern Chile, collected from published data. We observed two population-dynamics inflection points for these regions. First, starting at ca. 3000 BP, constant population growth occurred, which was related to horticulture in the Arica region and to agriculture in the Tarapacá region. Second, between ca. 1000 and 400 BP, a general population rise occurred due to the consolidation of intensive agriculture in the lowlands and precordillera altitudinal belts in both regions and the integration of the coast and the altiplano into macro-regional population dynamics.

Massive ground ice found in the Barrow Permafrost Tunnel at 3–7 m depths from the surface has been interpreted as an ice wedge and used to reconstruct early Holocene environmental changes. To better understand the development of this ground ice, we conducted radiocarbon dating for 34 samples of plant remains from the massive ground ice and underlying sediment layer. A significantly large gap in the measured radiocarbon ages (more than 24 ka) between massive ice and the underlying sediment layer throughout the tunnel profile suggested at least two possibilities. One is that the lower and older sediment layer had thrust upwards at the boundary between intruding ice wedge and adjacent sediment, and the growing ice had pushed the sediment sideways. Another is that erosional events had removed surface materials at about 12–36 ka BP (14–41 cal ka BP) before the overlaying sediment layer with massive ground ice developed. The overall distribution of radiocarbon ages from the massive ice supported the ice-wedge hypothesis as a formation mechanism, although our results showed several age inversions and large fluctuations. Dating of densely spaced samples revealed two ground-ice regions with similar ages around 11–11.5 and 10–10.5 ka BP divided by a relatively narrow region of transitional ages along the tunnel long-axis. This distribution may be explained by a possible misalignment between the sampling direction and the ice-wedge growth line or by intermittent ice growth with repeated cracking at more random locations than the classic ice-wedge growth model suggested.

In-situ cosmogenic 10Be (and 26Al) concentrations in alluvial sediments provide a spatially averaged signal of the erosion rate of the catchment area. Catchmentwide erosion rates reflect the production rate of the entire basin, and their calculation requires knowledge of the complete production rate model. Available calculators determine production rates on a pixel-based approach and achieve computational efficiency by relying on a scaling method that ignores geomagnetic field strength variations. Here we introduce a new python-based tool that determines erosion rates based on the hypsometry of the catchment. The method relies on the fact that production rates are much more sensitive to changes in elevation than latitude. Our tool has two main advantages: (1) computation time is short (<30 seconds) and independent of the scaling method; there is no need to neglect magnetic field variations, and (2) because production rate scaling is performed by a widely used online calculator, the results are fully comparable to exposure ages or point-based erosion rates determined with the same calculator; future updates to production rate scaling are immediately effective for catchmentwide erosion rate calculation. We demonstrate in two case studies that (1) for similar scaling methods, our calculator reproduces pixel-based results within a few percent, and (2) erosion rates determined with different scaling methods may differ by >20%, differences can vary systematically with erosion rate, and using a time-constant scaling method may result in a bias in the interpretation of catchmentwide erosion rates.

Skin-based samples (leather, skin, and parchment) in archaeological, historic and museum settings are among the most challenging materials to radiocarbon (14C) date in terms of removing exogenous carbon sources—comparable to bone collagen in many respects but with much less empirical study to guide pretreatment approaches. In the case of leather, the 14C content of materials used in manufacturing the leather can vary greatly. The presence of leather manufacturing chemicals before pretreatment and their absence afterward is difficult to demonstrate, and the accuracy of dates depends upon isolating the original animal proteins and removing exogenous carbon. Parchments differ in production technique from leather but include similar unknowns. It is not clear that lessons learned in the treatment of one are always salient for treating the other. We measured the 14C content of variously pretreated leather, parchment, skin samples, and extracts, producing apparent ages that varied by hundreds or occasionally thousands of years depending upon sample pretreatment. Fourier Transform Infrared Spectroscopy (FTIR) and C:N ratios provided insight into the chemical composition of carbon reservoirs contributing to age differences. The results of these analyses demonstrated that XAD column chromatography resulted in the most accurate 14C dates for leather and samples of unknown tannage, and FTIR allowed for the detection of contamination that might have otherwise been overlooked.