Study of ⁹⁹Tc and ¹²⁹I measurement using 3MV Xi’an-AMS

The 3 MV AMS is completely unable to distinguish isobars within a gas ionization chamber for medium-heavy mass nuclides such as ⁹⁹Tc and ¹²⁹I. However, isobar suppression and elimination can be performed during the extraction stage in the ion source. Due to the limited energy in 3 MV AMS, ⁹⁹Tc and ⁹⁹Ru can’t be separated, so it does not show sufficient advantages compared to ICP-MS. Therefore, ⁹⁹Tc analysis was rarely carried out using 3 MV or below AMS. In addition, ⁹⁹Tc as an artificial nuclide is confronted with no stable isotope for normalization. The ¹²⁹I was successfully analyzed by AMS due to the non-exitance of ¹²⁹Xe⁻. Xi’an-AMS is limited by hardware capabilities to only use a relatively inefficient + 5 charge state for measurement. In this work, the feasibility of ⁹⁹Tc analysis by 3 MV Xi’an-AMS was studied, and it was determined that ⁹³Nb molecules were used as the stable isotope for the normalization beam, carbides were used as the injected negative ions, and ⁹³Nb was used as the pilot beam. The transmission efficiency of the whole machine was tuned and optimized. ⁹⁹Tc correction with ⁹⁹Ru was discussed, and the detection limit of ⁹⁹Tc was estimated to be about ~ 10¹¹ atoms in this preliminary work. Furthermore, the measurement of ¹²⁹I³⁺ was established at Xi'an-AMS, the interferences in the measurement of + 3 charge state were analyzed, and the measurement of ¹²⁹I³⁺ and ¹²⁹I⁵⁺ was compared using real samples and process blank samples. Both of them were consistent within 1σ, but the total efficiency of the + 3 charge state is about 1.75 times higher than that of the + 5 charge state.