Abstract
Isotopic fractionation in the graphitization reaction for Radiocarbon Accelerator Mass Spectrometry measurements was evaluated. At LAC-UFF we use the TiH2/Zn reduction method, where H2 and Zn enable the reduction of CO2 into graphite. In previous works, we analyzed C stable isotopes ratio for different amounts of Zn in the range of 0–50mg and the results indicated that the amount of Zn is strongly linked to both the degree and variability of isotopic fractionation during the reaction when the quantity of TiH2 ranges from 10 to 15mg for samples containing between 0.7 and 1.0mg of C. For no changes in fractionation have occurred by increasing the graphitization temperature from 520°C to 550°C, in the present paper we evaluate the effects of different temperatures for the H2 release step. Previous works have also led us to question the role of Zn in the TiH2-based process and how it affects fractionation. Therefore, graphitization reactions without TiH2 or without Zn, using different amounts of TiH2, were tested. The former reaction has required values of Zn:C>50 while the latter is not recommended. When Zn:C=30, minimum amounts of TiH2 (TiH2:C<20) have led to reasonable results of isotopic fractionation (<2‰).
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