A radioactive source has an initial activity of 4,800 Bq. Calculate its activity after three half-lives have passed.

Nuclear Physics Challenge #3 — Activity & Decay

Activity after
three half-lives.

Nuclear Physics Medium

Problem

A radioactive source registers an activity of 4,800 Bq today. Calculate its activity after three half-lives have passed.

Initial activity\( A_0 = 4800\ \mathrm{Bq} \)
Elapsed time3 half-lives
Answer inbecquerels

Activity halves right alongside the number of undecayed nuclei.

Hint: activity is proportional to how many unstable nuclei remain — so it halves with every half-life, exactly like the mass did. Three halvings: \( \div 2^3 \).

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Activity afterthree half-lives.

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Activity after
three half-lives.