effective half-life (ehl), the time required for a radioactive element in an animal body to be diminished by 50% as a result of radioactive decay and biological elimination. The effective half-life is equal to the product of the biological half-life (bhl) and the radioactive half-life (rhl) divided by the sum of the bhl and the rhl: ehl=(bhl×rhl)/(bhl+rhl). See also biological half-life.
