Redetermination of low-level 99Tc in planchet samples by ICP-MS

Technetium-99 concentrations in environmental samples are usually very close to or under the detection limit of a radiation counter. In recent years, ICP-MS has been popularized to measure low 99Tc concentrations. Besides, the method is useful to check the concentration of determined 99Tc by a radiation counting method. Thus, in this study, ICP-MS has been used to re-measure 99Tc in samples prepared for a radiation counting technique. Subjected 99Tc sources were planchet samples on which Tc was electroplated after chemical separation from algae. The 99Tc activities were previously determined by radiation counting. Tc was continuously removed from each planchet sample with 2M HNO3 and 2M NaOH. During the first Tc dissolving step from the planchet with 2M HNO3, a small amount of Tc, which was thought to be fixed as TcO2, was dissolved. However, additional two extraction steps increased the percentage of extracted Tc to 93 - 97%. After the solution containing Tc was adjusted to 0.1M HNO3, Tc was extracted on a TEVA resin to concentrate Tc and to remove Ru. It was found that Tc was completely separated from Ru in the final solution for ICP-MS by our separation method. Thus, the isotope, whose mass was 99, could be identified as 99Tc. The results of 99Tc measurements by both radiation and ICP-MS methods agreed well with each other. The total recoveries for Tc on the planchet samples were almost the same, with an average of 91%. (author)