Institute of Imaging Methods, Faculty of Medical Studies

In the article “Exponential law of the radioactive decay”, rubric “Mixtures of radionuclides” general equation of successive decay of radionuclides A(lA)®B(lB)®C(stable) was derived. Applying this equation (multiplied by factor lTc in order to obtain the momentary activity in [Bq] from the momentary number of nuclei) to our case of the Mo-Tc generator 99Mo(lMo=0.0105 hour-1)®99mTc(lTc=0.1155 hour-1)®99Tc(“stable”) and taking into account the fact that 87 % of 99Mo decays to the metastable excited level of 99mTc, we can get for the time dependence of momentary activity of the desired technetium 99mTc the following relation: A99m-Tc(t) = 0,957.AMo(t=0) . (e-0.0105.t – e-0.1155.t ), where AMo(t=0) is activity of 99Mo at time t=0 of the previous elution, the time t being expressed in hours. The activity of 99Mo changes with time T by the decay law AMo(T) = AMo(0).e-lMo.T = AMo(0).e-0.0105.T. Using the insertion of this basic molybdenum decay we get the resulting relation for momentary activity of eluted 99mTc at time T from the delivery of the molybdenum generator and at time t elapsed from the latest elution: