How is half-life defined in relation to radioactive decay?

The definition of half-life in the context of radioactive decay is most accurately captured by the statement that it is the time required for half of a radioactive substance to decay. This concept is fundamental in the study of radioactivity and nuclear chemistry.

Half-life provides insight into the stability of isotopes, indicating how long it takes for a given quantity of a radioactive material to reduce to half of its initial amount. For example, if you start with 100 grams of a substance that has a half-life of 5 years, after 5 years, only 50 grams will remain. This decay continues, halving the quantity with each subsequent half-life, until the material is virtually undetectable, although it never fully reaches zero within a finite number of half-lives.

Understanding half-life is pivotal for applications in fields such as radiometric dating, nuclear medicine, and understanding the behavior of radioactive waste. The clarity provided by this definition allows chemists and physicists to predict how long it will take for a substance to reach a safe level of radioactivity or to evaluate the effectiveness of radiopharmaceuticals over time.