Browsing UA Faculty Research by Publisher "UNIV ARIZONA DEPT GEOSCIENCES"
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Assessment and Development of Bone Preparation for Radiocarbon Dating at HEKALBone is one of the most complex sample materials used for radiocarbon (C-14) dating. The installation of the EnvironMICADAS AMS at HEKAL (department of ICER) in 2011 required the adoption of new sample preparation techniques for small bone samples. Since then, hundreds of procedural background and known-age bones have been processed using our modified Longin method (MLM) and dated along with unknown samples. Their results are used in this study to assess the reproducibility of our current bone preparation method and the real uncertainty of the final age result. In addition, using the background samples, which are included in each bone measurement batch, blank correction of the unknown samples could also be performed. The mean (FC)-C-14 value of our bone blanks is generally better than 0.005 (similar to 42,500 BP) alongside 0.0013 SD. Good reproducibility was confirmed by the results of the laboratory known-age bone as well, where the standard deviation of the mean is better than 0.0025. In addition, the results of the three bone samples used in an ultrafiltration (UF) test study did not show notable differences from the ones obtained by our current protocol in 1 sigma uncertainty range but more experiments will be performed in the near future.
The Best possible Time resolution: How precise could a Radiocarbon dating method be?Today, accelerator mass spectrometry (AMS) technology enables us to carry out very precise measurements of radiocarbon (C-14). Unfortunately, due to fluctuations in the C-14 calibration curve, the resulting calibrated time intervals vary from decades up to centuries in calibrated age. Within a time scale of several decades, we can find several time intervals on the C-14 calibration curve which correspond with periods of rapid increases in atmospheric (CO2)-C-14 activity. Some of these "high slope" parts of the calibration curve could be used for fine time resolution for radiocarbon dating of individual samples. Nevertheless, there are certain limitations owing to the properties of the samples measured. We have prepared a time-resolution curve for the C-14 dating method, applying calibration curve IntCal13 and assuming an uncertainty of C-14 analyses +/- 15 yr BP (for recent samples). Our curve of the time resolution covers the last 50 ka. We found several time intervals with time resolution below 50 yr BP for the last 3 ka. Several time intervals which can enable substantially better time resolution compared to neighboring parts of the calibration curve were also found for periods older than 3 ka.
Dissolved Inorganic and Organic Carbon in an Ephemeral Fresh Water Stream in Southern ArizonaWe report on an initial long-term study of dissolved inorganic and organic carbon (DIC) from Sabino Creek, located in Sabino Canyon, Pima County, Arizona. The purpose of this study was to monitor changes in dissolved radiocarbon (14C) with time and to understand the processes contributing to these variations. Our results span the period 2009–2016 and show a mixing trend between dissolved inorganic and organic carbon modern end-members with an older component. This study provides preliminary information for more detailed research on recycling of organic components in this stream system.
Radiocarbon Dating and the Protection of Cultural HeritageThe modern antiquities market uses radiocarbon (C-14) dating to screen for forged objects. Although this fact shows the potential and power of the method, the circumstances where it is applied can be questionable and call for our attention. Here we present an outline of a call to radiocarbon laboratories for due diligence and best practice approaches to the analysis of antique objects requested by non-research clients.