Question

the time it takes for half of the atoms in an isotope to decay

Answer 1

A radioactive isotope decays at a constant rate proportional to the number of radioactive atoms remaining. A simple way of describing the speed of decay is to see the time it takes for half of the atoms of a radioactive parent to decay and form the daughter element(s). This is called the half life.

Answer 2

The time it takes for half of the atoms in an isotope to decay is known as the Half-Life of that isotope.

Knowing the half-life of an isotope is useful in many complex calculations.

Carbon Dating, for example, is a method conducted on the basis of the half-life of Carbon-14, whose half-life is of approximately 5700 years.