In this report, we describe the sample preparation system for AMS-14C at the National Museum of Japanese History, where more than 600 samples are prepared annually mainly for archaeological and historical researches. Our laboratory (Dating Materials Laboratory) started in 1998 and extended its space and equipments in 2004 to meet a requirement of increasing samples in our own research projects such as the project:"The origin of the Farming in the Yayoi Period and East Asia: Establishment of High-Precision Chronology by Carbon-14 Analysis". Our study policy are featured in two points: 1) Since we do not have our own AMS machine, 14C measurements are conducted as collaborative works between university AMS facilities or are commissioned to commercial AMS facilities. 2) AMS samples are prepared at our institute to keep high guarantee as much as possible. To meet this we concentrate in obtaining high quality data for research by collecting and examining samples which is most suitable for our research goals. This is because we believe that preparation and graphitization process has become the most important step in 14C -AMS dating, since the performance of AMS has now reached the level that we can get almost the same results at any facilities for the same graphite samples. Our sample preparation and graphitization procedures for archaeological samples are as follows: The sample was normally treated by conventional acid-alkali-acid treatment. The pretreated sample and CuO (II) together with Sulfix was combusted to CO2 at 850°C for 3h in a sealed quartz glass tube, and the CO2 gas was then purified by high vacuum line. The purified CO2 gas was reduced to the graphite with iron powder catalysis. We use the Sulfix at the first combustion step, so that it could be reduced the last SO2 desorption process in comparison with conventional purified method. To ascertain the absence of the contamination of carbon at the first sulfix combustion process, we investigated isotopic fractionation effect with Sulfix by measuring 14C/12C and d13C and assessed the influence of 14C background (or blank) levels.This work was supported by a Grant-in Aid for Creative Scientific Research of the Japan Society for the Promotion of Science (No.16GS0118).
See more of Poster Session II
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)