Physics and Radiobiology of Nuclear Medicine

Successive Decay Equations 31

Fig. 3.4. Plot of activity versus time on a semilogarithmic graph illustrating the tran-
sient equilibrium. Note that the daughter activity reaches a maximum, then tran-
sient equilibrium, and follows an apparent half-life of the parent. The daughter
activity is higher than the parent activity at equilibrium.

Fig. 3.5. Plot of logarithm of^99 Mo and 99mTc activities versus time showing transient
equilibrium. The activity of the daughter 99mTc is less than that of the parent^99 Mo,
because only 87% of^99 Mo decays to 99mTc. If 100% of the parent were to decay to
the daughter, then the daughter activity would be higher than the parent activity
after reaching equilibrium, as recognized from Eq. (3.17), and Figure 3.4.