A Bayesian model for accelerator mass spectrometry (AMS) data analysis is presented. Instrumental drift is modeled with a continuous autoregressive (CAR) process, and measurement uncertainties are taken to be Gaussian. All samples have a parameter describing their true value. The model adapts itself to different instrumental parameters based on the data, and yields the most probable true values for the unknown samples. The model is able to use the information in the measurements more efficiently. First, all measurements tell something about the overall instrument performance and possible drift. The overall machine uncertainty can be used to obtain realistic uncertainties even when the number of measurements per sample is small. Second, even the measurements of the unknown samples can be used to estimate the variations in the standard level, provided that the samples have been measured more than once. Third, the uncertainty of the standard level is known to be smaller nearer a standard. Fourth, even though individual measurements follow a Gaussian distribution, the end result may not.

For simulated data, the new Bayesian method gives more accurate results and more realistic uncertainties than the conventional mean-based (MB) method. In some cases, the latter gives unrealistically small uncertainties. This can be due to the non-Gaussian nature of the final result, which results from combining few samples from a Gaussian distribution without knowing the underlying variance and from the normalization with an uncertain standard level. In addition, in some cases the standard error of the mean does not represent well the true error due to correlations within the measurements resulting from, for example, a changing trend. While the conventional method fails in these cases, the CAR model gives representative uncertainties.

Although high-sensitivity liquid scintillation (LS) spectroscopy is theoretically capable of producing finite radiocarbon ages in the 50,000- to 70,000-yr range, there is little evidence in the literature that meaningful dates in this time period have been obtained. The pressing need to undertake calibration beyond 26 kyr has resulted in the regular publication of 14C results in excess of 50 kyr, yet very little effort has been made to demonstrate their accuracy or precision. There is a paucity of systematic studies of the techniques required to produce reliable dates close to background and the methods needed to assess contamination from either in situ sources or laboratory handling and processing. We have studied the requirements for producing accurate and reliable dates beyond 50 kyr. Laboratory procedures include optimization of LS spectrometers to obtain low and stable non-14C background count rates, use of low-background counting vials, large benzene volumes, long counting times, and preconditioning of vacuum lines. We also discuss the need for multiple analyses of a suitable material containing no original 14C (background blank) and the application of an appropriate statistical model to compensate for variability in background contamination beyond counting statistics. Accurate and reproducible finite ages >60 kyr are indeed possible by high-sensitivity LS spectroscopy, but require corroborating background blank data to be defensible.

The result from probabilistic calibration of a radiocarbon date is given in the form of a probability density function. Consequently, reporting a 68% or 95% confidence interval has became a commonly accepted practice. However, many users of 14C dates still try to present the results of calibration as a single point. This manner of presentation is often applied during the construction of age-depth models due to its convenience and simplicity. In this paper, the author tests whether it is possible to find a good point estimate of a calibrated 14C date. The idea of the tests is to compare, using computer simulation, the true value of the calendar age with the age calculated based on the probabilistic calibration of the 14C date and the method of finding the point estimate. The test is carried out for the following point estimates: mode, median, average, the central point of the confidence intervals, and the local mode inside the confidence intervals. The results show that none of these may be considered as a good estimate.

It is now almost 10 yr since radiocarbon dating of cremated bone was first developed using the small carbonate component contained within the hydroxyapatite-based inorganic fraction. Currently, a significant number of 14C laboratories date cremated bone as part of their routine dating service. As a general investigation of cremated bone dating since this initial development, a small, cremated bone intercomparison study took place in 2005, involving 6 laboratories. Six cremated bone samples (including 2 sets of duplicates), with ages spanning approximately 1500–2800 BP, were sent to the laboratories. The results, which showed relatively good agreement amongst the laboratories and between the duplicate samples, are discussed in detail.

The Fifth International Radiocarbon Intercomparison (VIRI) continues the tradition of the TIRI (third) and FIRI (fourth) intercomparisons (Scott 2003) and operates as an independent check on laboratory procedures in addition to any within-laboratory procedures for quality assurance. VIRI is a 4-yr project, with the first suite of samples (grain) sent out in September 2004 and the second suite (bone) sent out in December 2005. Further stages will include samples of peat, wood, and shell with a range of ages.

The 4 grain samples included 2 samples (A and C) of barley mash (20 g for radiometric analysis and 2 g for AMS), a grain (barley) byproduct from the manufacture of Glengoyne malt whiskey. The 2 remaining charred grain samples (B and D) were from excavations at Beth Saida and Tel Hadar, respectively (10 g for radiometric analysis and 4 seeds for AMS) and were provided by Elisabetta Boaretto of the Weizmann Institute. Consensus values for samples A and C are 109.2 (standard deviation [1 σ] = 2.73) and 110.6 pMC (1 σ = 2.48), and 2805 (1 σ = 162.7) and 2835 BP (1 σ = 190.8) for samples B and D, respectively. Sample A is a new sample that was collected in 2001, while sample C was used in the FIRI trial as samples G & J (consensus value 110.7 pMC) and was collected in 1998. The expected ages (on archaeological grounds) of samples B and D are 2800 BP and 2850–2900 BP, respectively. The second suite of samples comprises bone, ranging in age from Medieval to “close to background,” and was distributed in December 2005. Samples for both radiometric and AMS laboratories include E: mammoth bone (>5 half-lives); F: horse bone (from Siberia, excavated in 2001); and H, I: whalebone. Finally, sample G (human bone) was only for AMS laboratories. Some of the issues related to using bone in a laboratory intercomparison will be discussed.

All measurement is subject to error, which creates uncertainty. Every time that an analytical radiocarbon measurement is repeated under identical conditions on an identical sample (even if this were possible), a different result is obtained. However, laboratories typically make only 1 measurement on a sample, but they are still able to provide an estimate of the analytical uncertainty that reflects the range of values (or the spread) in results that would have been obtained were the measurement to be repeated many times under identical conditions. For a single measured 14C age, the commonly quoted error is based on counting statistics and is used to determine the uncertainty associated with the 14C age. The quoted error will include components due to other laboratory corrections and is assumed to represent the spread we would see were we able to repeat the measurement many times.

Accuracy and precision in 14C dating are much desired properties. Accuracy of the measurement refers to the deviation (difference) of the measured value from the true value (or sometimes expected or consensus value), while precision refers to the variation (expected or observed) in a series of replicate measurements. Quality assurance and experimental assessment of these properties occupy much laboratory time through measurement of standards (primary and secondary), reference materials, and participation in interlaboratory trials. This paper introduces some of the most important terms commonly used in 14C dating and explains, through some simple examples, their interpretation.

A preliminary determination of the absolute 14C/12C ratio of the oxalic acid I standard (NBS SRM 4990B) has been made. Using an accelerator mass spectrometry (AMS) system, a known number of radiocarbon ions were implanted in a thin copper foil. The foil was then combusted with the addition of 14C-free carrier material. This resulting gas (which had a known 14C/12C ratio) was graphitized and compared to OX-I material. This comparison yielded an absolute 14C/12C ratio of OX-I. The absolute 14C/12C ratio of OX-I, coupled with knowledge of the specific activity of OX-1, provides an alternative determination of the 14C half-life.

It is well known that radiocarbon years do not directly equate to calendar time. As a result, considerable effort has been devoted to generating a decadally resolved calibration curve for the Holocene and latter part of the last termination. A calibration curve that can be unambiguously attributed to changes in atmospheric 14C content has not, however, been generated beyond 26 kyr cal BP, despite the urgent need to rigorously test climatic, environmental, and archaeological models. Here, we discuss the potential of New Zealand kauri (Agathis australis) to define the structure of the 14C calibration curve using annually resolved tree rings and thereby provide an absolute measure of atmospheric 14C. We report bidecadally sampled 14C measurements obtained from a floating 1050-yr chronology, demonstrating repeatable 14C measurements near the present limits of the dating method. The results indicate that considerable scope exists for a high-resolution 14C calibration curve back through OIS-3 using subfossil wood from this source.

We have measured the radiocarbon ages of 43 consecutive single-year tree rings using accelerator mass spectrometry (AMS) with a statistical accuracy of ∼2.3%. AMS 14C ages of the 36 viable samples are between 2708 and 2666 cal BP, a period in which the Δ14C of the IntCal04 curve (Reimer et al. 2004) shows an enhancement. The 14C ages of the samples are scattered with a Gaussian distribution around the interpolated IntCal04 calibration curve. The time profile of the deviations of the 36 14C ages from the interpolated IntCal04 calibration curve indicates a linear trend and a characteristic variability rather than a random fluctuation around the curve. The trend indicates a higher gradient than that of the interpolated IntCal04 calibration curve. The profile implies a periodic variation of approximately 11 yr and an amplitude of roughly 18 14C yr.

When constructing absolute chronologies in archaeology, the aim is to detect archaeological events. In this respect, we draw attention to the relation between the radiocarbon ages of human bone collagen samples and the absolute dating evidence on the age at death. In recent material, Mebus Geyh (2001a,b) described the offset between the former and the latter, and suggested the relevant correction. The corrected 14C ages pertain to the age of the individual at death.

We have developed an application of Geyh's original observation, which we term the human bone collagen offset (HBCO) correction, to apply to archaeological 14C dates. If the death and interment of individuals are identical, the corrected 14C date reliably informs us about the deposition of the body and accompanying grave goods. In archaeology, the concrete correction value is determined by the anthropologically estimated age of the individual, which we model by a normal (Gaussian) distribution. The eventual impact of the HBCO correction on archaeological chronology depends on the portion of the calibration curve through which the HBCO-corrected date is calibrated. At a certain level of 14C measurement precision, the difference between the HBCO-corrected and non-corrected calendar dates can be considerable.

In order to investigate the regional atmospheric radiocarbon offset, accelerator mass spectrometry (AMS) 14C measurements were made on 5-yr increments of a Japanese wood sample dendrochronologically dated to 820–436 BC. The 14C data from the Japanese tree-ring samples were compared with the IntCal04 calibration curve (Reimer et al. 2004). In most parts, the differences between IntCal04 and 14C dates in the Japanese tree-ring samples were within experimental statistical errors. At around 680 BC, however, significant differences of up to 100 14C yr were observed. These differences may indicate either regional offsets in Japan or the short-term fluctuation of a subdecadal timescale in atmospheric 14C variations.

An important archaeological survey was conducted by Leonard Woolley and T E Lawrence in 1914 on behalf of the Palestine Exploration Fund in the Negev and northeastern Sinai deserts—the “Wilderness of Zin.” The region of Ain Kadeis, associated by some scholars in the 19th century with biblical Kadesh-Barnea, received much attention in their survey and discussions. Concerning the vexed question of Kadesh-Barnea, Woolley and Lawrence gave their preference for the nearby Ain el Qudeirat Valley, and in particular the ancient tell. Their survey contributed significantly in the shaping of scholarly opinion on the matter, even until today. But modern surveys and excavations failed to identify any archaeological remnants of the 2nd millennium BCE in the above regions, thereby putting the above associations in question. The Middle Bronze Age II, Late Bronze Age, and Iron Age I that cover this millennium are considered missing in the area in archaeological terms. However, our research reveals that archaeological remains of the 2nd millennium BCE do exist in the region, as determined chronologically by radiocarbon dating. A geoarchaeological approach is required to investigate terraced fields in wadis, which contain a unique record of human activity in these desert regions.

The urnfields in western Belgium have been studied since the second half of the 20th century. Most of these studies, as well as the excavations themselves, date from before the last quarter of the 20th century, except for the urnfields at Velzeke and Blicquy, which were excavated recently. The chronology of these cemeteries was largely based on typochronological studies of pottery. Other funeral gifts, like bronze objects in the graves, are rather exceptional. The typochronology was worked out in a comparison with the framework of neighboring regions and central Europe. There was a need, then, for a chronology based on absolute dates. This was only possible by radiocarbon dating of the cremated bones. Tests on duplicate samples, like cremated bone in context with charcoal or 2 depositions of cremated bones within 1 urn, have shown that the results are reproducible and that there is no discrepancy between the charcoal and the cremated bone dates.

The results of the 14C dating project on the cremated bones of the 2 urnfields at Velzeke and the one at Blicquy are promising. The interpretation of the occupational history of both sites at Velzeke can be revised, and the currently accepted ceramic sequence for this period needs reworking. In addition, the chronological framework of the Late Bronze Age and Early Iron Age is open for discussion. It seems plausible that the urnfield phenomenon starts earlier in western Belgium than previously expected. These dates can also contribute to the discussion about the transition from the Late Bronze Age to the Early Iron Age.

Given the fluctuating nature of the radiocarbon calibration curve, the precision of single 14C dates on the calendar timescale is limited. However, 14C dating combined with dendrochronology enabled us to date timbers found in the Tisza River, Hungary, during the dry period of summer 2003. Routine preparation of wood samples gave 14C results spread over 4 centuries. By extracting alpha-cellulose from the samples, 2 distinct and relatively narrow historical time periods were obtained: the first period (AD 1505–1595 and 1612–1673, respectively) coincided with the Turkish occupation period, while the second interval (1733–1813) obtained in the case of 2 samples did not exclude the existence of another bridge constructed later. The dendrochronological data confirmed that the bridge was constructed from oak timbers felled between 1558 and 1565. The 14C and dendrochronological dates correspond with the date of a letter written in 1562 by Antal Verancsics, Bishop of Eger, mentioning the construction of the first bridge. In conclusion, the archaeological excavation revealed proof of the first historically attested wooden bridge over the Tisza River.

Newly obtained radiocarbon measurements are used to suggest that the initial settlement of the northeastern Baltic area was largely controlled by the Ladoga-Baltic waterway in the north of the Karelian Isthmus, which emerged ∼11,500 cal BP and remained in action for ∼7000 yr. The transgression of Ladoga Lake started ∼5000 cal BP and reached its maximum at ∼3000 cal BP (∼1100–1000 cal BC). The formation of a new outlet via the Neva River led to a rapid regression of the lake that stimulated the spread of farming populations.

Reference archaeomagnetic secular variation (SV) curves recently have been proposed for the Iberian Peninsula and may now be used for archaeomagnetic dating. Archaeomagnetic dating is a relative dating technique that is strongly dependent on the age control of the data used to construct the reference curves. In order to test the method, an archaeological structure from central Spain has been studied. Samples have been taken for both archaeomagnetic and radiocarbon dating, and the results are compared. Close agreement is observed between both techniques, with the archaeomagnetic age of AD 603–999 overlapping the calibrated age of AD 770–890. These results demonstrate the reliability of the proposed reference curves as a dating tool within the Iberian Peninsula during this archaeological period.

The people of the Paracas and Nasca cultures, the creators of the famous geoglyphs, lived in the desert of the southern coast of Peru between about 800 BC and AD 650. The archaeological chronology of these cultures has been based almost exclusively on a sequence of ceramic styles. The absolute dating of some of the style phases was supported by a few radiocarbon dates (Rowe 1967). Here, we present an absolute chronology of the Paracas and Nasca cultures based on 14C dating of more than 100 organic samples from settlement and tomb relics, as well as on material derived from geoglyph sites in the Nasca/Palpa region (south Peru). The main focus has been on Nasca period settlement centers near Palpa, Los Molinos and La Muña, the Paracas period site of Jauranga, and the Initial period site of Pernil Alto. Most of the 14C samples were dated at the accelerator mass spectrometry (AMS) facility of the ETH Zurich (Switzerland). The targets were produced in the newly built graphitization line at the Heidelberg 14C laboratory (Germany). Clay (adobe) bricks, which are quite a common building material in Peru, were successfully tested to be used for AMS 14C dating of adobe architecture in Peruvian archaeology.

The ongoing Ychsma Project aims to shed light on the chronology and function of the late Prehispanic period at the well-known archaeological site of Pachacamac, Peru, through extensive archaeological research. The Temple of the Monkey is a special building that has been cleared, mapped, and excavated within the general framework of the study of “pyramids with ramps,” the most common form of monumental architecture at the site. Through the application of radiocarbon measurements, it can be shown that the temple has been used for around 150 yr and therefore is quite different from other pyramids with ramps previously studied (see Michczyński et al. 2003). Details of the temple, 14C sample selection, and methodology, as well as results, are discussed in this paper. The research has allowed us to make significant advances in the current understanding of pyramids with ramps and the function of the site of Pachacamac as a whole.

This paper presents a suite of new accelerator mass spectrometry (AMS) radiocarbon measurements from the Ayacucho Valley of Peru and discusses their implications for the timing and nature of the collapse of the Wari Empire. Analysis of these and previously published dates from the region indicate that there is little evidence for state political authority in Ayacucho prior to the end of the 7th century. Dated human remains from the polity's eponymous capital indicate that the authority of the state's rulers persisted at least as late as the mid-11th century. Dates from rural sites in the Ayacucho Valley suggest continuity of occupation and folk material culture following Wari's disintegration. Finally, AMS measurements of bone from 2 large extramural ossuaries represent the first absolute dates associated with Chanca ceramics and suggest that this archaeological/ethnohistoric culture appeared in the valley at about AD 1300.

This paper outlines the radiocarbon program applied to the excavation and skeletal assemblage from the cemetery of the medieval Priory and Hospital of St. Mary Spital in London. Problems encountered in dating medieval cemeteries are outlined. The problems were addressed through the application of Bayesian modeling to validate and refine conventional approaches to constructing phases of archaeological activity. It should be noted that this project was solely funded by the developer of the land; such projects rarely undertake even modest programs of 14C dating. We aim to show how the investment of a proportionally small sum, compared to the overall project costs, may reap significant benefits.