Question detail
A radioactive isotope has a half-life of 5 years. If the initial activity is 80 Bq, what will the activity be after 15 years?
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At a glance
Question
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Topic
Atoms and nuclear radiation
Question
A radioactive isotope has a half-life of 5 years. If the initial activity is 80 Bq, what will the activity be after 15 years?
Answer
10 Bq
Explanation
10 Bq is correct because the worked solution uses remaining = initial / 2^n and substitutes the values from the question. This keeps activity, count rate, atomic number, mass number and neutron count distinct for Atomic structure.
Common mistake
Misunderstanding Half-Life Calculations
Students often confuse the concept of half-life with the total decay time, leading to incorrect calculations of remaining count rate or activity.
To accurately calculate the remaining count rate after a number of half-lives, remember that each half-life reduces the count rate by half. Use the formula: remaining count rate = initial count rate × (0.5)^n, where n is the number of half-lives.
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