Estimation of chemical effect on the decay rate of sup(99m)Tc

The chemical effect on the decay rate of the 2.17-keV isomeric transition of sup(99m)Tc has been studied theoretically. Simplified estimation of the effect is presented, where calculations of the internal-conversion probabilities for various subshells are made and the relative change in lambda for two kinds of pairs are estimated. The results are lambda(TcO4-) - lambda(Tc2S7) = 3.27 x 10-3 lambda(Tc2S7) and lambda(Tc2S7) - lambda(metal) = 3.15 x 10-4lambda(metal). The present theoretical treatments are not accurate enough for the quantitative discussion, but give the reasonable explanation to the experimental results. (author)