# Effective half-life

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:

:$\left\{lambda_e\right\} , = \left\{lambda_p\right\} , + \left\{lambda_b\right\} ,$

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

:$t_\left\{1/2\right\} = frac\left\{ln \left(2\right)\right\}\left\{lambda_e\right\}$

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

* [http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/biohalf.html Biological Half-life]

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