Biological half-life

Biological half-life

Biological half-life is the time required for a radioactive substance to reduce to half its original amount in a biological organism, through excretion and absorption. The biological half-life depends on the half-life of the radioactive isotope in question, and the amount of it being absorbed and/or excreted from the biological organism. Therefore, biological half-life can range from seconds to hundreds of years.

http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/biohalf.html