Preliminary research on method of tree ring’s NE-OBT measurement using AMS

Abstract The non-exchangeable organically bound tritium (NE-OBT) concentration in the cellulose of tree rings can accurately reflects the tritiated water concentration in the local environment and often contains the only historical record of tritium exposure. However, there is few study about NE-OBT measurement using AMS around the world, especially in China. Furthermore, in order to measure tritium in tree rings exactly, it is necessary to solve several key problems during sample preparation. In this study, the optimized sample preparations procedure are investigated. The purity of cellulose extracted by improved sodium hypochlorite pretreatment method is about 83.9%, considerably higher than the 64.8% conventional methods. Pure TiH 2 samples reaching requirements of AMS measurement have been made. The isotope fractionation is stabilized during sample preparation. Preliminary results of sample analysis using a compact AMS with 200 kV accelerator are presented. Currently, the minimum T/H ratio that can be accurately measured is only about 10 −12 , limited by hydrogen contents in samples and instrument conditions. Further works will be done in order to achieve lower detection limits and better accuracy.