NOVEL LASER ABLATION SAMPLING DEVICE FOR THE RAPID RADIOCARBON ANALYSIS OF CARBONATE SAMPLES BY ACCELERATOR MASS SPECTROMETRY

摘要

Conventional radiocarbon analysis of carbonate records with accelerator mass spectrometry (AMS) is time consuming and the achievable spatial resolution is limited, because individual samples have to be taken and need to be converted to graphite for the measurement. A new laser ablation (LA) in situ sampling technique for rapid online C-14 analyses of carbonate records by AMS is presented. By focusing a 193-nm ArF excimer laser on carbonate samples, carbon dioxide is generated and can directly be introduced into the gas ion source of an AMS. A dedicated LA cell for AMS was constructed in a way that combines rapid gas exchange with the capacity to carry sample specimen with maximum dimensions of 15x2.5x1.5 cm(3). With the presented setup, negative carbon ion currents up to 20 mu A were achieved. A low C-14 background of 0.011 +/- 0.002 (FC)-C-14 was observed on C-14-free marble and different standard and reference materials could be well reproduced within errors. The novel technique allows scanning carbonate samples continuously over several cm per hour with achievable measurement precisions of less than 1% for modern samples. This approach allows acquiring highly spatially resolved C-14 records at a far higher rate than with any currently available method.