HALF-LIVES OF TECHNETIUM-97, TECHNETIUM-98

Re-determination of half-lives of Tc-97 and Tc-98, both geochemically and astrophysically important isotopes, has been attempted. Tc-97 and Tc-98 isotopes were produced by Mo-95(alpha,2n)Ru-97 --> Tc-97 and Mo- 97(d,n)Tc-98 reactions. For Tc-97, the number of atoms in the source w as evaluated from the known amount of the parent nuclides Ru-97, and t he activity was determined by the measurement of Mo K X-rays in refere nce to the Tc K X-rays emitted in the isomeric transition of a known a mount of Tc-97m. The half life of Tc-97g was gotten as (4.0 +/- 0.3) x 10(6) y. The branching ratio of Ru-97 decaying to Tc-97m, and half-li ves of Ru-97 and Tc-97m were newly determined to be 0.017%, 2.791 +/- 0.004 day and 92.2 +/- 1.8 day, respectively. As for Tc-98, the EC dec ay was expected from mass and decay scheme data with emission of two g amma-rays, 0.722 MeV and 0.787 MeV, in cascade. But no clear photopeak s were observed and the upper limit for EC/beta(-) was estimated to be < 0.04. The number of Tc-98 atoms in the source still must be determi ned accurately, but a rough estimate showed that the half-life of Tc-9 8 was of the order of 10(6) y.