Techniques for making precise and accurate radiocarbon accelerator mass spectrometry (AMS) measurements on samples containing less than a few hundred micrograms of carbon are being developed at the NOSAMS facility. A detailed examination of all aspects of the sample preparation and data analysis process shows encouraging results. Small quantities of CO2 are reduced to graphite over cobalt catalyst at an optimal temperature of 605°. Measured 14C/12C ratios of the resulting targets are affected by machine-induced isotopic fractionation, which appears directly related to the decrease in ion current generated by the smaller sample sizes. It is possible to compensate effectively for this fractionation by measuring samples relative to small standards of identical size. Examination of the various potential sources of background 14C contamination indicates that the sample combustion process is the largest contributor, adding ca. 1 μg of carbon with a less-than-modern 14C concentration.

A new set of radiocarbon dates from a rockshelter in Mendoza, Argentina addresses the question of the temporal overlap between the presence of an unidentified extinct ground sloth (cf., Mylodontidae) and evidence of human activity. Dung balls on the cave floor, evidently deposited by sloth, are overlain by charcoal, apparently of cultural origin. 14C dates, mostly on charcoal and dung from this shelter, calibrated using recently published curves, as well as the stratigraphy of the deposits from which the samples were collected, suggest that any co-occurrence of humans and ground sloths in this region was brief. In contrast, the single date on mylodon dermal ossicles from this shelter suggests significant time overlap. Replication of this date as well as obtaining new high-precision 14C analyses from this site will be the next priority.

We measured radiocarbon ages of 11 pieces of ancient Japanese documents by accelerator mass spectrometry (AMS). The purpose of this study is to compare the relationship between the calibrated 14C age and the historical age of Japanese paper samples. Calibrated ages of nine pieces agree with their historical ages, indicating that Japanese ancient documents can be used for 14C dating in the recent historic period. On the other hand, the 14C age of paper that was used for reinforcement of a sutra is ca. 300 yr older than the historical age of the sutra. This shows that the sutra was repaired with old paper.

The accepted state-of-the-art 14C dating method relies on calibration curves to determine initial 14C levels in a sample. The paper reconsiders the basis of 14C dating and offers a possible alternative that eliminates the need to employ calibration curves. The idea is to measure the level of radiogenic nitrogen atoms retained in the sample molecules after 14C β-decay. The practicality of this alternative method still has to be proven.

After routine accelerator mass spectrometry (AMS) radiocarbon dating had been established at the Leibniz-Labor with the completion of systems for CO2 production, graphitization, and target making, a systematic investigation was conducted to find the sources of 14C concentrations observed in background materials. We quantified the contributions of the AMS-system, the reduction, CO2 production from carbonate, carbonate contamination, and combustion. Carbonate contamination appears to be the dominating factor. Improvements in the pretreatment of foraminifer carbonate have led to the elimination of most of this contamination.

In May 1995 an impressive karstic cave possessing dozens of burials dating to the main phase of the Chalcolithic Period (ca. 4500–3500 bce) was discovered in Peqi'in in the high hills of Galilee in northern Israel. It was subsequently excavated over the course of the following months. The large amount of unique ceramic ossuaries and the variety of burial offerings shed light, for the first time, on this critical societal development period in a region where its remains have rarely been found. Although the major significance of the cave is as a mortuary center, it was also utilized in a domestic capacity some centuries previously, during the generally less familiar Early Chalcolithic Period. We present here the dating of 22 14C samples collected from these separate phases of cave use. Their interpretation should aid in understanding of the absolute dating of the Chalcolithic Period and its relation to the period preceding its inception.

We present here new radiocarbon dates for the different barrows (burial mounds) of the nomadic tribes of the Scythian period in the Khakassia and Tuva regions (Central Asia). The time scale of these barrows is compared with the elite barrows of the Sayan-Altai. In agreement with archaeological evidence, some barrows in Khakassia are chronologically close in time to the Arzhan barrow. The first 14C dates produced for the barrows from the Tuva region belong to a later Scythian period, compared with the elite Arzhan barrow. We determined the final stage of the barrow construction, but to establish the starting time, more dates are necessary (both by dendrochronology and 14C).

For very small samples, it is difficult to prepare graphitic targets that will yield a useful and steady sputtered ion beam. Working with materials separated by preparative capillary gas chromatography, we have succeeded with amounts as small as 20 μg C. This seems to be a practical limit, as it involves 1) multiple chromatographic runs with trapping of effluent fractions, 2) recovery and combustion of the fractions, 3) graphitization and 4) compression of the resultant graphite/cobalt matrix into a good sputter target. Through such slow and intricate work, radiocarbon ages of lignin derivatives and hydrocarbons from coastal sediments have been determined. If this could be accomplished as an “online” measurement by flowing the analytes directly into a microwave gas ion source, with a carrier gas, then the number of processing steps could be minimized. Such a system would be useful not just for chromatographic effluents, but for any gaseous material, such as CO2 produced from carbonates. We describe tests using such an ion source.

The carbon concentration in CuO and iron was determined by isolating C. The values were in agreement with results reported in other studies. Contaminating carbon from CuO and Fe was transformed to AMS targets and measured for 14C. C-traces in CuO were shown to be the major contribution to the 14C sample processing blank. In addition, there is a significant variability in the 14C content of CuO observed between different production batches. The combined contamination potential of CuO and Fe was found to be 4.47–8.92 μg recent carbon, whereas the more realistic estimate for AMS-target preparation conditions ranged between 1.63 and 3.24 μg recent carbon, depending on the 14C level in CuO.

In the opencast mine area of Zwenkau, Germany, many prehistoric wells and pits have recently been excavated. In this region there is generally no bone preservation and charred seeds are rare, seldom encountered in a reliable archaeological context, whereas charcoal is frequently found. From an archaeological point of view, however, charcoal from wood is not as reliable for radiocarbon dating as short-lived materials. Fortunately, many deep features were found where wood has been preserved. Over a dozen structures turned out to be prehistoric wells, some of them typologically dated by ceramics to between Early Bronze Age and Early Middle Ages. For other features without archaeological finds, 14C dating was the only way to get an age. Analysis showed that different types of wells were constructed by the same culture. On the other hand, the same constructions are not characteristic for a defined cultural period and were applied over a time span of three millennia.

Does radioactive decay follow the Poisson distribution?—a fundamental question, to which the theoretical answer seems to be, Yes. On the practical side, the answer to this question impacts the best achievable precision in well-controlled counting experiments. There have been some noteworthy experimental tests of the Poisson assumption, using systems carefully designed for the analysis of individual pulses from stable radioactive sources; thus far, experiment supports theory. For low-level counting, the nature of the background distribution can be of profound practical importance, especially for very long counting experiments where validation by an adequate number of full replicates may be impracticable. One is tempted in such cases to assume that the variance is equal to the mean, in order to estimate the measurement uncertainty. Background radiation, however, has multiple components, only some of which are governed by the laws of radioactive decay.

A specially designed low-level gas counting system at NIST for interactive, retrospective individual pulse shape and time series analysis makes possible the investigation of the empirical distribution function of the background radiation, in a manner similar to the previous empirical distribution studies of radioactive decay. Benefits of individual pulse analysis are that there is no information loss due to averaging and that two independent tests of the Poisson hypothesis can be performed using data from a single, extended measurement period without the need for replication; namely, tests of the distribution of arrival times, expected to be uniform, and the distribution of inter-arrival times, expected to be exponential. For low-level counting the second test has a very interesting and very informative complement: the distribution of coincidence-anticoincidence inter-arrival times.

Key outcomes from the study were that: 1) nonstationarity in the mean background rate over extended periods of time could be compensated by an on-line paired counter technique, which is far preferable to the questionable practice of using an “error-multiplier” that presumes the wandering (nonstationary) background to be random; and 2) individual empirical pulse distributions differed from the ideal GM and Poisson processes by exhibiting giant pulses, a continuum of small pulses, afterpulses, and in certain circumstances bursts of pulses and transient relaxation processes. The afterpulses constituted ca. 8% of the anticoincidence background events, yet they escaped detection by the conventional distributional tests.

With >40 14C dates, mainly on bones and charcoal, the site at Son Mas is the only megalithic sanctuary on the Balearic Islands that has been dated by 14C in detail. Although soil erosion made stratigraphy difficult and the monument was cleaned out regularly during its long use, the results demonstrate that the site was occupied from the Pretalayotic (Chalcolithic) until the Roman period. The aim of this study was not only to date the construction and the use of the sanctuary, but also to correlate this monument, by means of dispersion diagrams, with the other prehistoric sites situated within the same valley. The dates were also used to compare the site with the generally accepted chronology of the Balearic archipelago (Mallorca, Menorca, Ibiza and Formentera).

Until recently, the only chronometric technique applied to Sahulian archaeological sites was 14C dating; the ages obtained rarely exceeded 40,000 bp. Belief that the region was first colonized around that time has recently been shaken by luminescence dates from several archaeological sites in northern Australia that suggest people arrived between 60,000 and 55,000 bp. The ensuing debate over their validity revealed that some participants misunderstood luminescence dating and the temporal limitations of 14C dating, illustrated here through a discussion of the tempo and mode of Sahulian colonization. Radiometric techniques cannot distinguish between the models proposed because they are unable to resolve temporal issues that occur within their limits of error.

The application of traditional gas or liquid scintillation counting (LSC) is necessary for assessing radionuclide activity in countries without operating accelerator mass spectrometry (AMS) facilities. A simple and relatively inexpensive system of mini gas counters for measurement of radiocarbon in archaeological and environmental samples has been set up recently in the Kraków laboratory (Department of Environmental Physics, University of Mining and Metallurgy). The system is composed of a gas purification and counter filling line, three identical 15-mL copper/quartz counters, active and passive shielding, and an electronic unit with data acquisition. One counter measures 22 mg of carbon as CO2 with efficiency >95% at a background reduced to 0.044 cpm by a NaJ(Tl) guard counter and lead shield. The detection limit (1 σ) for a two-week measurement of 48 mL of CO2 is 0.52 pMC. The corresponding counting error of a 100 pMC environmental sample is 1.3 pMC for 22 mgC (one counter) and 0.75 pMC for 66 mgC (three counters filled with the same sample).

Since 1994, a new data-acquisition system with rise-time (RT) based background reduction has been in operation at the Gliwice Radiocarbon Laboratory. During long-term stability tests, we observed large shifts in the RT spectra obtained during various measurement series. These shifts caused important changes in the count rate measured with RT reduction. As a result, we have ascertained that the shifts are the consequence of variable concentration of electronegative impurities. A correction method was considered, using average RT of pulses obtained in coincidence with the muon events, so-called ARTL (average rise time of L pulses), for estimation of the RT of the spectrum's shift. However, radiocarbon dates calculated based on count rates with RT discrimination, which were corrected using this method, are not more precise than traditional 14C dates. Nevertheless, the value of the average coincidence pulse RT is a good indication of sample gas purity.

A large number of 14C dates for archaeological sites in European Russia have been entered into a new database. The database includes >1500 dates for ca. 500 archaeological sites. Because European Russia is a very large area, the database includes subdivisions of territories and regions. We analyzed our 14C dates according to archaeological periods (Paleolithic through Medieval period) and made a comparison with environmental (climatic) parameters. Our database for archaeological sites and monuments offers new possibilities for correlation between the development of ancient cultures and natural-climatic processes.

The first radiocarbon dates for the famous monuments of European Scythia were produced for the Kelermes, Seven Brothers, Solocha and Chertomlyk barrows (burial mounds) by both accelerator mass spectrometry (AMS) and conventional methods. The obtained 14C dates confirmed the traditional archaeological chronology, which was based on the analysis of written data and typological comparisons of Scythian artifacts with similar objects found in the Ancient East and Greece. The 14C dates for the European Scythian monuments are compared with the Asian ones. The 14C chronology of the European Scythian monuments shows chronological synchronisms between the Asiatic and European monuments. The calibrated ages for the investigated barrows generally agree with the archaeological data.

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.

Kunashir Island is a very important site for paleoenvironmental reconstructions. Until recently, very little information on Quaternary deposits was available. We studied the environmental evolution of this oceanic island under the influence of geomorphological processes, volcanism and strong marine currents. This paper presents new data that allow a detailed reconstruction of the environmental development of Kunashir Island during the Late Pleistocene–Holocene, based on ca. 80 radiocarbon dates and diatom, pollen and sedimentological data. The vegetation development reflects climate changes and warm/cold current migrations.

β-counting software programs were developed and installed in new PCs for operation under a Windows® NT workstation. The new software programs allow us to simultaneously control several β-counting systems, either remotely or from within the laboratory. This setup is much less expensive than our previous arrangement, which required a separate PC for each counter.