The half life of a specific Tc-99m is 6 hours. How much of an 192 mg sample will have decayed after 30 hours?

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Quizplus · Accepted Answer

After 30 hours, which is 5 half-lives (30 hours / 6 hours per half-life), a very small fraction of the original 192 mg of Tc-99m would remain. Specifically, after each half-life, the amount remaining is halved. So, after 5 half-lives, $192 mg \times (\frac{1}{2})^5 = 192 mg \times \frac{1}{32} = 6 mg$ remains. Therefore, 192 mg - 6 mg = 186 mg will have decayed.

The Half Life of a Specific Tc-99m Is 6 Hours