A radioisotope has decay constant λ. If its activities at times t₁ and t₂ are A₁ and A₂, respectively, find the number of nuclei that decay between t₁ and t₂.
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Question

A radioisotope has decay constant λ. If its activities at times t₁ and t₂ are A₁ and A₂, respectively, find the number of nuclei that decay between t₁ and t₂.

G1 Physics · Accepted Answer

Activity A = λN, so N₁ = A₁/λ and N₂ = A₂/λ. The number that decays between t₁ and t₂ is N₁−N₂ = (A₁−A₂)/λ. Correct answer: B.