What does half-life mean?

What does half-life mean?

• A. The time for the entire sample to decay
• B. The time for half the sample to evaporate
• C. The time it takes for half of a material to decay
• D. The time for the sample to be replaced

Answer: (C)

Half-life is the time required for half of the radioactive nuclei in a sample to decay, so the amount of radioactive material drops to half its initial value. This is an exponential process: after each half-life, the remaining activity is halved. It’s a property of the substance and depends on its decay constant, not on how large the sample is or how long you wait beyond that period. The decay constant relates to half-life by t1/2 = ln 2 / λ. In practical terms, if a substance has a half-life of T, after T time units you’ll have about half as much radioactivity left, after 2T you’ll have about a quarter, and so on. This concept is about decay, not evaporation or replacement of the material.

Half-life is the time required for half of the radioactive nuclei in a sample to decay, so the amount of radioactive material drops to half its initial value. This is an exponential process: after each half-life, the remaining activity is halved. It’s a property of the substance and depends on its decay constant, not on how large the sample is or how long you wait beyond that period. The decay constant relates to half-life by t1/2 = ln 2 / λ. In practical terms, if a substance has a half-life of T, after T time units you’ll have about half as much radioactivity left, after 2T you’ll have about a quarter, and so on. This concept is about decay, not evaporation or replacement of the material.