A radioactive material initially is observed to have an activity of 1 000 decays/sec.If three hours later it is observed to have an activity of 125 decays/sec,what is its half-life?

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Quizplus · Accepted Answer

The activity decreases from 1000 to 125 decays/sec, which is a reduction by a factor of 8 (1000 to 500 to 250 to 125). This corresponds to three half-lives (since 1000/2 = 500, 500/2 = 250, 250/2 = 125). Since this occurs over 3 hours, the half-life is 1 hour.

A Radioactive Material Initially Is Observed to Have an Activity