The zinc reduction method for converting CO2 to graphite for AMS 14C measurements was developed originally for rapid production of graphite in the biomedical field. The method was usually thought to have low precision and a high background. We have modified the zinc reduction method by carefully controlling the amounts of reagents (zinc, titanium hydride and Co/Fe) and now routinely obtain a precision of 2-3‰ and a relatively low background of 50,000 year when analyzing for 14C at the Keck AMS facility at UC Irvine. Fractionation of carbon isotopes does occur during the graphitization depending on the amount of reagents used and other conditions. δ13C of graphite can be lighter by 1 to 6 ‰ than the CO2 from which it is made, but this is corrected for in our system by the simultaneous 13C/12C measurements by the AMS. This method is not only suitable for 14C enriched samples but also for many applications dealing with natural 14C level samples, especially those with modern 14C contents. With improved precision and background, we believe that many disciplines can benefit from this technique because of its low cost and rapid production of graphite.
See more of Poster Session II
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)