On the use of 99Mo/99mTc generators in the analysis of low levels of 99Tc in environmental samples by radiochemical methods

The analysis of low levels of the long-lived fission product Tc-99 in environmental samples presents special challenges, particularly with respect to the selection of an appropriate and practicable chemical yield tracer. Of all the tracers available, Tc-99m eluated from Mo-99/Tc-99m generators appears to be the most practicable in terms of availability, ease of use and cost. These factors have led to an increase in the use of such generators for the provision of Tc-99m as yield tracer for Tc-99. For the analysis of low levels (<1Bq/m(3) or kg) of Tc-99 in environmental samples, consideration must be given to the radiochemical purity of the tracer solution with respect to contamination with both Tc-99 and other radionuclides. This paper details investigations carried out in relation to the use of Mo-99/Tc-99m generators for the provision of 99mTc for use as yield tracer in the analysis of low levels of Tc-99. The results of the study indicate that special care must be taken with the radiochemical purity of the Tc-99m solution. Analysis of eluates from a number of such generators indicates the presence of Ru-103 and Tc-99 in levels that could produce inaccuracies in the analysis of low levels of Tc-99. Results are presented and the findings discussed with reference to low level Tc-99 analysis by radiochemical procedures and beta counting.