What is a half life?

Answer by  ShanL (684)

This term refers to the amount of time it takes a substance to decay to the point where only half of it is left (so it has decreased by 50%).

Answer by  palaeologus (564)

The period of time that must elapse before precisely half of a quantity of a radioactive element (such as uranium) decays, thereby becoming either another element or another isotope of the same element.