The activity of a sample of radioactive bismuth decreases to one-eighth of the original is 15 days. Its half-life is:
Correct answer: D. 5 days
- A. 10 days
- B. 15 days
- C. 3 days
- D. 5 days
Explanation
The half-life of a radioactive substance can be determined based on the time it takes for the activity (or the number of radioactive atoms) to decrease to one-eighth (1/8) of its original value. In this case, the activity has decreased to one-eighth of its original value in 15 days. Since the activity is halved every half-life, it's reasonable to assume that three half-lives have passed in 15 days, as 1/23 =1/8 . Therefore, the half-life of the radioactive bismuth is 15 days divided by 3, which equals 5 days. So, the half-life of the bismuth is 5 days.
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About Half-life and Rate of Decay
Half-life is the time required for half the unstable nuclei in a sample to decay, and it remains constant for a particular radioactive nuclide. Questions use the exponential decay law, decay constant, activity, remaining quantity and mean life. Radioactive decay is random for individual nuclei but predictable for large samples.
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