What does the term 'half-life' refer to in radioactive decay?

The term 'half-life' in the context of radioactive decay specifically refers to the time required for half of a given sample of a radioactive substance to undergo decay. This concept is fundamental in nuclear chemistry because it provides a measure of the stability of a radioactive isotope.

During each half-life period, the amount of the original radioactive material decreases to half its initial quantity. For example, if you start with 100 grams of a radioactive isotope that has a half-life of 10 years, after 10 years, you would have 50 grams remaining, then 25 grams after another 10 years, and so forth. This evidence of decay illustrates how half-lives are not only critical for understanding the decay process but also for applications such as radiometric dating and medical therapies.

The other options do not accurately capture the meaning of half-life, as they refer to different concepts. Some might suggest total decay or the average lifespan of an element, but those definitions misrepresent the specific and quantifiable nature of half-life as a periodic measure of decay for just half of the sample, rather than the entirety.