We present the first Bayesian 14C modeling based on AMS ages from stratified sediments representing continuous occupation across the Early Bronze III/IV interface in the Southern Levant. This new high-precision modeling incorporates 12 calibrated AMS ages from Khirbat Iskandar Area C using OxCal 4.4.4 and the IntCal 20 calibration curve to specify the EB III/IV transition at or slightly before 2500 cal BCE. Our results contribute to the continuing emergence of a high chronology for the Levantine Early Bronze Age, which shifts the end of EB III 200–300 years earlier than the traditional time frame and increases the length of EB IV to about 500 years. Data from Khirbat Iskandar also help direct greater attention to the importance of sedentary communities through EB IV, in contrast to the traditional emphasis on non-sedentary pastoral encampments and cemeteries. Modeling of AMS data from Khirbat Iskandar bolsters the ongoing revision of Early Bronze Age Levantine chronology and its growing interpretive independence from Egyptian history and contributes particularly to re-examination of the EB III/IV nexus in the Southern Levant.

The sets of core samples were distributed to over 120 laboratories that had returned an original questionnaire seeking expressions of interest in participation. A reporting format for the results was also agreed and distributed to the laboratories at the same time. This is shown in Table 2.1. Laboratories were originally given 1 yr (i.e., to August 2000) to complete the analyses and return the results, but this was later extended to December 2000. In this section, we briefly describe the laboratory characteristics and the overall response rate of the participating laboratories.

The radiocarbon dating laboratory of Queens College, CUNY, was established with the joint support of the Research Foundation of the City University of New York and the departments of Anthropology, Biology, Chemistry, and Earth and Environmental Sciences of Queens College. The laboratory has been operational since June, 1975 and is located in the basement of a two-story concrete and brick building.

Radiocarbon analysis of freshwater dissolved organic carbon (DOC) involves substantial sample pretreatment, including an initial rotary evaporation stage necessary to concentrate large volumes of freshwater sample. This may lead to a health risk from the exposure to pathogens, and there is the additional concern that the warm conditions during the rotary evaporation stage may provide ideal growing conditions for some pathogens. To remove any pathogen risk in water samples, boiling or autoclaving can be undertaken. However, to date, no studies have been undertaken to investigate whether boiling will alter the 14C signature of dissolved organic carbon. Here, we analyze the effect of sterilization on 9 contrasting river water samples. Comparing filtered, filtered and boiled, and filtered and sterilized dissolved organic matter, we observe that both boiling and autoclaving increases the uncertainty associated with the 14C and 13C of DOC, that the 14C and 13C changes are not unidirectional, and that they are not related to original DOC composition. Neither sterilization method is recommended unless essential, in which instance we recommend a 3σ uncertainty on 14C and that the 13C is not considered representative of the original sample.

As an alternative to the accelerator technique, a simple, compact, small counter system has been developed and tested for routine 14C dating. Our small counter is an all-metal design made of the OFHC copper with quartz supports for the anode (25μm stainless steel). Careful selection of materials for the counter construction was made based on the measurements of the alpha contamination. Methane as the counter filling gave better resolution and gas gain stability, whereas CO2 gave lower background counting rate and it was easier to prepare and to handle. The long term run using CH4 showed that the gas gain remained stable within 1–2% for months after the initial drop which followed the counter filling. A 7-day counting period was sufficient to achieve a 3% relative standard deviation which was considered acceptable for routine dating of younger samples.

Accelerator mass spectrometry (AMS) radiocarbon dating and paleoecological analysis of slope deposits at Mt Raizan provided seven 14C dates indicating that landslides occurred in that area at 6.0 to 6.3 cal ka BP and 6.5 cal ka BP. Plant macrofossils, pollen grains, and spores point to a mixed forest at that time, consisting of conifers and broad-leaved trees. On the other hand, insect fossil indicates slightly colder climate than that of the flora. This difference may be attributed to varied sensitivities of each proxy to climatic changes.

Samples reported in this date list are primarily geologic specimens collected from coastal locations in South Carolina and Florida. Sample material was predominantly shells, with emphasis on single shell dates rather than multiple shell dates. Archaeologic samples from sites either directly above or adjacent to the geologic sampling location were collected whenever possible to provide an upper time limit on the shell deposits.

This list contains the results of measurements of 172 radiocarbon samples made between January 1983 and December 1985. An additional 152 samples were measured, but these were submitted without detailed information, such as sample location and sampling depth; therefore, they were excluded from the list.

This list includes results of measurements made during 1973-1974 and 1975 in the Natural Radiocarbon Laboratory of the Centre de Recherches Radiogéologiques de Nancy (CRR).

We report results of a three-year intercomparison experiment between the WHOI Radiocarbon Laboratory (now at University of California, Irvine) and the NSF-University of Arizona AMS Laboratory. The purpose of this study was to compare high-precision measurements of samples obtained routinely using gas proportional counting techniques with results obtained using AMS techniques. Three sets of annually banded, modern coral samples were used for the intercomparison. Each sample was acidified to CO2 at WHOI and split into two fractions. The larger fraction was converted to acetylene gas and counted at WHOI in quartz, gas-proportional beta counters. The smaller fractions were converted to graphite and analyzed for 14C using AMS techniques at the University of Arizona. Results of the three sample sets are presented. Except for a single outlier, the data from the two laboratories are in good agreement. Of the 13 samples in the third set of the intercomparison, for which a new high-intensity ion source was in operation at the Arizona AMS laboratory, agreement of results is excellent. This finding indicates that measurements made with precisions of < 3% are reproducible at both laboratories.

A new facility for radiocarbon dating by accelerator mass spectrometry (AMS) was established in early 2015 at the Inter-University Accelerator Centre in New Delhi, India. The facility uses a 500 kV National Electrostatic Corporation (NEC) Pelletron accelerator for AMS measurements on graphite produced using the automated graphitization equipment (AGE) interfaced with an elemental analyzer and the carbonate handling system (CHS). A precision of better than 1‰ in the ratio of 14C/12C for the modern carbon sample and the background level of 1 × 10–15 from dead carbon sample has been achieved. This is the first dedicated accelerator of India only for AMS activities. This AMS system has the capabilities to perform 10Be and 26Al measurements as well.

A standard heavy ion nuclear structure facility has been used to detect several long-lived radioisotopes by counting the accelerated ions. The problem of eliminating strong isobaric background beams has been solved by combining the energy loss dispersion through a uniform Al foil stack with the high momentum resolution of an Enge split-pole magnetic spectrograph. Radioisotope concentrations in the following ranges have been measured: 14C/12C = 10–12 to 10–13, 26Al/27Al = 10–10 to 10–12, 32Si/Si = 10–8 to 10–14, 36Cl/Cl = 10–8 to 10–11.

During the past year we have continued to work toward greater stability and flexibility in nearly all elements of our accelerator mass spectrometry (AMS) system, which is based upon an FN tandem Van de Graaff accelerator, and have carried out measurements of 14C/12C and 10Be/9Be isotopic abundance ratios in natural samples. The principal recent developments and improvements in the accelerator system and in our sample preparation techniques for carbon and beryllium are discussed, and the results of a study of 10Be cross-contamination of beryllium samples in the sputter ion source are presented.

The results presented in this list have been obtained by benzene synthesis and liquid scintillation counting: ages are calculated using the 14C half-life of 5570 yr with 0.95 activity of NBS oxalic acid as modern standard, with no correction. The given precision is obtained from a one-standard-deviation criterion.

The dates in this list follow, in approximately chronologic order, those reported in Harwell III (R, 1979, v 21, p 358–383). It is confined to archaeologic samples from the United Kingdom only, most of which originate from “rescue” type operations supported by the Historic Buildings and Monuments Commission for England, (formerly a section of the Dept. of the Environment) and submitted through the Ancient Monuments Laboratory, London.