What does half-life mean?

A half-life refers to the time required for half of the measured atoms in a sample to go through radioactive or nuclear decay. The half-life of a specific isotope is constant, regardless of the initial quantity of atoms present or the amount of time it is sitting around.

When Ernest Rutherford discovered the half-life principle in 1907, the term used was "half-life period." It was condensed to "half-life" in the early 1950s.

Each radioisotope has its own half-life. The symbol for half-life is t with a subscript ½. The number of remaining radioactive isotope can be derived by using the formula: N(t) = N(0) x (0.5)^number of half-lives, where N(t) is the remaining amount of radioisotope, N(0) is the initial amount of radioisotope and the number of half-lives is the quotient of time and half-life.