Answer the following question given this paragraph: 

The disintegration of unstable nuclei does not occur all at once. The rate of disintegration is a statistical process. The most convenient way to consider it is by a concept known as half-life . The time required for half of the atoms in any given quantity of a radioactive substance to decay is the half-life of that element. Each particular isotope has its own half-life. For example, the half-life of radium-226 is 1600 years. That is, beginning with 1.00 gram of radium-226, it would take 1600 years for half of it to decay and leave 0.50 gram remaining. After another 1600 years, only 0.25 gram would remain. In each half-life, exactly half of the beginning amount decays.


Q: What is the time it takes for radioactive substance to decay?


A:
half-life