Radionuclides transient equilibrium

Figure 11,8 Composite decay curves for (A) mixtures of independently decaying species, (B) transient equilibrium, (C) secular equilibrium, and (D) nonequilibrium, a composite decay curve b decay curve of longer-lived component (A) and parent radio nuclide (B, C, D) c decay curve of short-lived radionuclide (A) and daughter radionuclide (B, C, D) d daughter radioativity in a pure parent fraction (B, C, D) e total daughter radioactivity in a parent-plus-daughter fraction (B). In all cases, the detection coefficients of the various species are assumed to be identical. From Nuclear and Radiochemistry, G. Friedlander and J. W. Kennedy, Copyright 1956 by John Wiley and Sons. Reprinted by permission of John Wiley and Sons Ltd.

O Equations (40.8) and (40.9) reduce to N1/N2 - /I2//I1 and Ai = A2. In these equilibria, the daughter activity will not exceed the parent activity. This characteristic, different from the transient equilibrium shown in O Fig. 40.1, is illustrated for the Ge/ Ga radionuclide generator in Fig. 40.3. The ratio between the mother and daughter half-lives in this case is 270.8 X 24h/1.135h = 5726. 

If however the short-lived radionuclide has a long-lived parent nuclide from which the former activity is produced genetically, the parent activity can be purified by standard radiochemical techniques. Then, after the establishment of transient radioactive equilibrium, the daughter activity Is separated from the parent by rapid radiochemical techniques In which the time to separate the nuclide from the parent must be considered. 

The MOTIF code is a three-dimensional finite-element code capable of simulating steady state or transient coupled/uncoupled variable-density, variable- saturation fluid flow, heat transport, and conservative or nonspecies radionuclide) transport in deformable fractured/ porous media. In the code, the porous medium component is represented by hexahedral elements, triangular prism elements, tetrahedral elements, quadrilateral planar elements, and lineal elements. Discrete fractures are represented by biplanar quadrilateral elements (for the equilibrium equation), and monoplanar quadrilateral elements (for flow and transport equations). 

Generally, the decay of a radioactive nuclide results in a longer-lived or even stable daughter nuclide. In this respect, radionuclide generator systems where the daughter nuclide presents a shorter half-life are a welcome exception from the general properties of P decay. In particular, for a clinical application, a state of a radioactive equilibrium is mandatory. Thus, mainly the transient and secular equilibria of radionuclide generations are relevant for... 

---