Effective half-life

Effective half-life denotes the halving of radioactive material in a living organism by means of radioactive decay and biological excretion. A decay constant is needed to calculate the half-life. It is the sum of the biological and physical decay constants, as in the formula:


 * $${\lambda_e} \, = {\lambda_p} \, + {\lambda_b} \,$$

With the decay constant it is possible to calculate the effective half-life using the formula:


 * $$t_{½} = \frac{\ln 2}{\lambda_e} \,$$

The biological decay constant is often approximated as it is more difficult to accurately determine than the physical decay constant.