Highly-resolved radiocarbon measurements on shells from Kalba, UAE, using carbonate handling system and gas ion source with MICADAS

摘要

The Mini Carbon Dating System (MICADAS) represents a flexible AMS system for measuring radiocarbon samples either in the form of graphite or CO2 gas. We used the possibility to attach a carbonate handling system (CHS) to the gas ion source (GIS) to measure smaller amounts of carbonates ( 500 mu g) than is usually required for graphite samples (1 mg). We determined a blank correction for different sample sizes ((FC)-C-14 ranging from similar to 0.0045 to similar to 0.017) from graphs. The use of OXA II as solid target and as gas fed through the GIS is presented. Cross-contamination is detected to be in the range of similar to 6%, but depends on the sample size and C-14 content of the previous sample. Our system delivers reliable data for sample sizes down to 30 mu g C when enough blanks (here 3) are used to clean the system. We tested the CHS-GIS combination on heated and unheated archaeological shells of Anadara uropigimelana from Kalba, Sharjah Emirate, United Arab Emirates (UAE). Even though the amount of carbon in the samples was small (4-22 mu g C) the performance of the CO2 dating system permits the comparison of trends in the C-14 data to stable isotope measurements (delta O-18 and delta C-13). With 10-20 mu g C, however, our sample sizes were too small, suffering from cross-contamination and elevated blanks, and our blank samples prior to the small samples were not enough. Hence, an interpretation in combination with the stable isotope data was not possible beyond comparison of trends.