Radiocarbon Sample Preparation Based On The Flam-Sealed Zn/Fe Reduction Method In Accelerator Mass Spectrometry Analysis

Abstract

: An alternative radiocarbon sample preparation with the flame-sealed Zn/Fe reduction method by removing the reagent of TiH 2 was developed, and the specifications and practices are described in detail. The graphitization parameters were optimized with 5 mg Fe powder (-325 mesh; H 2 -reduced spherical particles) as the catalyst, 15 mg Zn dust as the sole reductant and a reduction temperature of 500 °C for 3 h, followed by 550 °C for 4 h. The μm-scale morphology indicated that the spherical Fe particles were coated with a mix of graphite sheets and fuzz carbon. Simultaneously, SEM–EDS, XRD and XPS verified that the graphite-Fe target consisted of mostly graphitizable semidisordered carbon and Zn-Fe crystals, with minimal amounts of ZnO and Fe 3 ZnC crystals, which jointly ensured good performance (high and stable ion current output and good thermal conductivity) during the AMS measurements. The average fraction modern values of the SRM OX-II (consensus value, Fm=1.3407 ± 0.0019) and SRM IAEA-C7 (consensus value, Fm=0.4953 ± 0.0012) samples prepared from 2017 to present were 1.3403 ± 0.0058 (n=73) and 0.4964 ± 0.0031 (n=18), respectively. Thus, the long-term precision of the Zn/Fe sealed tube method was better than 6‰ and good accuracy was achieved over several years. The average background 14 C age of inorganic material was 43392 ± 1489 yr BP (n=44), and the ages of two 14 C-free organic materials were 45285 ± 2016 yr BP (n=15) and 46388 ± 2306 yr BP (n=36), indicating that low and stable carbon contamination levels were maintained throughout the entire chemical preparation process and AMS measurement over the last couple of years. The consistency between measured values and preferential values makes us confident in the preparation of various types of natural samples at normal mass size with our established vacuum line using the flame-sealed Zn/Fe reduction method.