Science Fact Finder | Chemistry and Physics - What Does Half-Life Mean?

What does half-life mean?

Half-life is a measure of the rate of decay of a radioactive element (an element that has the tendency to break down spontaneously into one or more elements). Specifically, it is the time it takes for the number of radioactive nuclei originally present in a sample to decrease to one-half of the original number. If a material has a half-life of one year, for example, its radioactivity will be reduced to one-half of the original amount after one year, and to one-quarter of the original amount after two years. The half-life of a given radioactive material is always the same, regardless of temperature, chemical combination, or any other condition.

Examples of elements that have radioactive isotopes include uranium, radium, and potassium. (Isotopes are forms of a chemical element having different atomic weights.

Sources: Barnhart, Robert K. The American Heritage Dictionary of...

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