Radiocarbon dating of archaeological samples (sambaqui) using CO_2 absorption and liquid scintillation spectrometry of low background radiation

摘要

Sambaqui means, in the Tupi language, a hill of shells. The sambaquis are archaeological sites with remains of pre-historical Brazilian occupation. Since the sambaqui sites in the Rio de Janeiro state region are older than 10,000 years, the applicability of CO_2 absorption on Carbo-sorb~® and ~(14)C determination by counting on a low background liquid scintillation counter was tested. In the present work, sambaqui shells were treated with H_3PO_4 in a closed vessel in order to generate CO_2. The produced CO_2 was absorbed on Carbo-sorb~®. On saturation about 0.6 g of carbon, as CO_2, was mixed with commercial liquid scintillation cocktail (Permafluor~®), and the ~(14)C activity determined by counting on a low background counter, Packard Tricarb 3170 TR/SL, for a period of 1000 mins to enable detection of a radiocarbon age of 22,400 BP. But only samples with ages up to 3500 BP were submitted to the method because the samples had been collected in the municipality of Guapimirim, in archaeological sambaqui-type sites belonging to this age range. The same samples were sent to the ~(14)C Laboratory of the Centro de Energia Nuclear na Agricultura (CENA/USP) where similar results were obtained.