What is Half-Life? (Chemistry)

Period after which only half of the original number of nuclei in a sample of a radioactive element have not decayed.

ex.   half-life for uranium – 238           ²³⁸₉₂U

= 4.6 x 10⁹ years

So after 4.6 x 10⁹ years, only one half of the original uranium will be left