Question detail
A radioactive substance has an initial count rate of 160 counts per minute. After 3 half-lives, what is the remaining count rate?
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At a glance
Question
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Topic
Atoms and nuclear radiation
Question
A radioactive substance has an initial count rate of 160 counts per minute. After 3 half-lives, what is the remaining count rate?
Answer
20 counts/min
Explanation
20 counts/min 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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