Radiochemical Analyses Through Polarographic Methods—II: Rapid Procedure for Technetium and Ruthenium Radionuclides In Fission Products*

Abstract

Summary Techniques have been developed for using polarographic methods in the analysis of radioactive isotopes. These new techniques consist essentially of removing the radioactive isotope of interest from a sample solution by amalgamating it with Hg from a dropping Hg electrode at a given potential and then assaying this amalgam by a radioactivity measurement. This technique was applied in developing the following accurate and rapid procedure for the analysis of Tc 99m and Ru 103,106 in fission-product mixtures: (1) an aliquot is removed from a solution of fission products and evaporated to dryness; (2) the residue is dissolved in a supporting electrolyte of 1 M sodium citrate-0.l M NaOH and this solution is placed in the polarographic cell; (3) a potential of 1.55 V vs. the S.C.E. is applied. The Tc and Ru are selectively amalgamated with the dropping Hg. The Hg is then separated from the solution by falling through CCl 4 and assayed by gamma counting. The amalgam is recounted after decay of the Tc 99m to provide data for computing the separate Tc 99m and Ru 103,106 counts. Corrections were also made for decay of Tc 99m during the period of time from the start of mercury collection to the time that the count is made; variation in collection time of Hg drops; simultaneous growth (from Mo 99 ) and depletion (~ 0.07 per cent min − 1 ) of Tc 99m during the time of collection. Test results for Mo by the polarographic method in which the daughter element, Tc 99m , is separated and counted, agree within 2 per cent with those obtained by the conventional method in which Mo 99 is precipitated with α-benzoinoxime. The relative standard deviation based on forty- eight determinations by the former method was 0.8 per cent, whereas, for forty-four determinations by the latter method, the standard deviation was 1.8 per cent. Good radiochemical purity is indicated for the polarographically separated Tc 99m and Ru 103,106 by half-life measurements, by gamma spectrometric analysis and by assaying the Hg collected as drops at 1.55 V vs. the S.C.E. from solutions containing known amounts of the most abundant fission product radionuclides. Decontamination factors of about 10 5 are obtained. A single separation of Tc 99m (and Ru 103,106 ) by the polarographic method requires about 3 min. The rapidity of the entire assay procedure (including data reduction) may be estimated by the fact that 48 analyses noted above were completed in 1 day by two people. For comparison, about eight Mo 99 or Ru 103,106 analyses can be made per day by one analyst, utilizing conventional methods. The aliquot size of the fission-product mixture needed for the present polarographic determination of Tc 99rn (and Ru 103,106 ) is larger by about a factor of 10 than that required by conventional analytic methods. The Hg collected during a period of 3 min from a solution of a 3 day old fission-product sample of 10 12 fissions will give approximately 15,000 d/min of Tc 99m and 300 d/min of Ru 103 .