Radiocarbon dating of bone by accelerator mass spectrometry

A companion article describes the sample preparation method used in the production of graphite targets for the Oxford accelerator mass spectrometer (AMS) system. The chemical pretreatment developed for the dating of bone, ivory and tooth samples is described in this paper.     

A dendrochronological analysis of Pinus pinea L. on the Italian mid-Tyrrhenian coast

In order to assess the response of the radial growth of Pinus pinea L. to climatic variability in Central Italy, dendrochronological and dendroclimatological analyses were carried out on five different populations scattered along the Tyrrhenian coasts of the peninsula. The aim of this study is to contribute to the understanding of the ecological demands of this species, particularly in the study area. For each site total ring, early-, and late-wood width chronologies were developed. Multidimensional analyses were performed for the three tree-ring datasets in order to analyze the relations between sites chronologies. Both Principal Component Analyses and hierarchical classifications highlighted an important difference of one site in respect to the other, probably due to site characteristics. Correlation functions were performed to infer the main climatic factors controlling the radial growth of the species. For a comparative study, we limited our attention to the common interval 1926–2003 (78 years) in which the response of the tree-ring chronologies to climate at both local and regional scale was investigated. Positive moisture balance in the late spring-summer period of the year of growth is the climatic driver of P. pinea radial growth in the study area. Moreover, this study shows how low summer temperatures strongly favor the radial growth of the species.     

Thermoluminescence dating

Over the last few years the Nordic Laboratory for Thermoluminescence (TL) Dating has obtained TL dates for a considerable number of archaeological samples, ceramics, bricks, burnt clay and burnt stones from the Nordic countries. The majority of TL dates have been consistent and in agreement with other dating evidence. Discrepancies caused primarily by excessive short‐term fading of the latent TL signal were encountered in a few cases. A procedure for eliminating errors caused by short‐term fading is described. A brief discussion of the sources of error in TL dating is given. Finally, results obtained by TL are compared with those obtained by radiocarbon for a number of sites.     

Pedogenetic dating of loess strata

Loess is an aeolian Pleistocene sediment of periglacial or arid origins, deposited without internal stratification in parcels representing geological periods. The contents of total as well as individual carbonates are comparatively uniform within a specific stratum, but the relative carbonate contents differ significantly between the various glacials as represented by loess facies. There is a consistent increase in the content of dolomite with decreasing age of stratigraphic units, which has traditionally been attributed to postdepositional alteration, notably the gradual removal of the calcite fraction by weathering. The explanation of pedogenetic enrichment in the course of aeolian recycling of glacial and glacio-fluvial deposits could convincingly account for the stepped profile of the dolomite's depth functions. The implication is that such recycled sediments can be attributed to specific cryocratic phases simply by their characteristic dolomite fraction, i.e. they can be dated. In order to test this hypothesis against the competing weathering hypothesis, strata of the Gudenus Cave in Lower Austria were subjected to carbonate differentiation analysis. The results are presented, analyzed and discussed. It is shown that the dolomite contents of the unweathered strata provide a clear trend that is even more pronounced than that found at open-air sites.     

Seasonal dating from fish frequencies

The method of seasonal dating from fish remain suggested by Leach is shown to be unsatisfactory. The method requires catch statistics that are at present unavailable. More important, when the method proposed for manipulating the data was applied to a set of hypothetical data, the results were not an accurate reflection of what was a very clear-cut situation.     

The archaeology of radiocarbon accelerator dating

Accelerator mass spectrometry (AMS) allows radiocarbon dating to be carried out by direct counting of¹⁴C atoms, rather than the conventional counting of radioactive disintegrations. The result is that samples up to 1000 times smaller can be handled. The approach was tested in principle by 1977 and for archaeological operation by 1983. More than 2000 samples per year are now being dated worldwide. The machines can now operate to about ± 80 years or better. Dates older than 40,000 years have not yet been achieved, but the ability to use small samples has already had considerable impact on dating the period 10,000–30,000 years ago. Bone is an ideal material for the new technique, since amino acids can normally be isolated and purified from gram-size samples. Studies of the origins of domestication are aided by the dating of individual grains and seeds. Because small samples can be mobile in the soil, careful sample selection strategies and procedures are required. The full impact of the technique can be assessed only through the rapid and comprehensive publication of archaeological results.     

A dendrochronological investigation of stringed instruments from the collection of the Cherubini Conservatory in Florence,Italy

A total of forty-nine stringed instruments of the Conservatory Cherubini collection, at the Musical Instruments Department of the Accademia Gallery in Florence, were submitted to a dendrochronological investigation in order to date them, check the validity of their attribution and to find out more about their construction characteristics. Thirty-seven instruments were successfully dated, thereby determining the terminus post quem date of manufacture. The correlation values of the statistical cross-dating tests were generally very high. The dendrochronological analyses determined which instruments had been made from wood of the same provenance and, in some cases, from the same tree trunk. The mean chronology built from the musical instrument series, named “Accademia Master Chronology”, is 558 years long and dates from 1396 to 1953AD. The interval between the youngest ring dated dendrochronologically and the given date of manufacture increased constantly in the course of the centuries, from a mean value of just over eleven years for instruments built in the eighteenth century, to nearly 74 years in the twentieth century, when the use of old wood from other artefacts became more frequent. Furthermore, in the Cherubini Collection, the average tree rings on violins are smaller than those of other stringed instruments; in fact, they increase in proportion to instrument size and are widest in cello and double bass.     

Sample preparation for accelerator-based radiocarbon dating

Although several efficient sample preparation methods have been devised for conventional radiocarbon dating, the advent of the accelerator mass spectrometer (AMS) dating technique with its much smaller sample requirement and different counting method has meant that new preparation routes have had to be developed. Techniques used for the Oxford AMS system are described in this paper.     

Radiocarbon dating by the accelerator technique

Radiometric dating of archaeological samples by the accelerator mass spectrometry (AMS) technique is well established today. The main advantage of this method compared to the old decay counting procedure is the small sample size (1 mg carbon equivalent weight) needed to carry out a dating. The basic principles as well as the present status of the technique are presented. Experiences from the first year of routine measurements in the Uppsala laboratory are discussed and some examples of the material analysed are given.     

Rehydroxylation dating of fired clays: an improved time-offset model to account for the effect of cooling on post-reheating mass gain

Dating of fired clay ceramics can be critical in building chronologies of archaeological sites. However, direct dating techniques such as luminescence, archaeomagnetism and radiocarbon dating are not always suitable or even possible. Rehydroxylation dating of fired clays is a developing method that has the potential to provide an alternative/complementary approach. Determination of a second stage, Stage II, mass gain rate in fired/reheated clay ceramics using a time^1/4-based model is central to this method. Experiments on modern brick samples demonstrate that the Stage II mass gain is not linear with t^1/4 as expected. The non-linearity observed can be taken account of through the introduction of a time-offset that represents the additional time required for mass gain at a specific aging temperature to equate to the additional mass gained above this aging temperature during cooling of the sample post-firing/reheating. Simulations of the mass gain curves expected during post-firing/reheating cooling highlight the significant effect of this mass gained during cooling and provide excellent agreement with experiment. Simulations also suggest that the two-stage structure in the mass gain curves observed might be better explained as largely the result of a single t^1/4-based process (Arrhenius in temperature dependence) across both stages; Stage I results from mass gained during cooling with Stage II resulting from mass gained during static temperature conditions. The overall implications for the dating method are that a non-linear Stage II mass gain (as a function of time^1/4) is expected and that an improved time-offset model provides a solution while removing issues of subjectivity in isolating the Stage II mass gain rate. This should lead to an improvement in the accuracy of RHX dates produced on archaeological material and further its development as a viable dating technique.