Question detail
A radioactive isotope has a half-life of 10 years. If the initial count rate is 800 counts/min, what will the count rate be after 30 years? Use the radiation safety context to keep Half-lives and the random nature of radioactive decay distinct from nearby atomic and nuclear radiation ideas.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Atoms and nuclear radiation
Question
- A. 100 counts/min (halflives and the random nature)
- B. 200 counts/min (halflives and the random nature)
- C. 400 counts/min (halflives and the random nature)
- D. 50 counts/min (halflives and the random nature)
Answer
The correct answer is 100 counts/min (halflives and the random nature).
Explanation
The correct answer is 100 counts/min (halflives and the random nature). It supports the learning objective: Calculate the number of half-lives that have passed from a change in activity or count rate.. The correct answer is 100 counts/min (halflives and the random nature). It directly supports the learning objective: Calculate the number of half-lives that have passed from a change in activity or count rate.. In Half-lives and the random nature of radioactive decay, this is the best option because it matches the specific radiation safety context; the other options mix up nearby ideas such as activity, count rate, isotope notation, radiation type, or nuclear-equation changes.
Common mistake
Counting Half-Lives Mistake
Students often miscalculate the number of half-lives that have passed by not correctly halving the initial count rate multiple times.
To fix this, students should clearly outline the initial count rate and systematically halve it for each half-life until they reach the final count rate, ensuring they count the number of halvings accurately.
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