Practical Generator Kinetics

Abstract

Equations describing the decay and buildup of nuclides in the ⁹⁹Mo–^99mTc generator are presented and discussed. The three basic time functions which describe the quantities of ⁹⁹Mo, ^99mTc, and ⁹⁹Tc are then manipulated to yield time-dependent factors which simplify the calculations of generator decay. These factors are (A) the fraction of maximum ^99mTc radioactivity at t hr following prior elution, (B) ^99mTc radioactivity as a fraction of ⁹⁹Mo radioactivity at time t following prior elution, and (C) The mole fraction of total technetium present in the generator as the metastable isomer at time t. These factors allow simple and accurate calculations of relative yields of ^99mTc at different times following prior elution, expected yield in millicuries and generator elution efficiency, and total molar quantity of technetium eluted. Examples are presented. Solutions of the basic differential equations are described in detail in the Appendix.