A radioactive source has a half-life of 2 min. At time t = 0 it is placed near a detector and the counting rate is observed to be 3000 counts/s. If the detection efficiency is 25%, how many radioactive nuclei are there at time t = 2 min?

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Quizplus · Accepted Answer

The number of radioactive nuclei at time t = 0 is:N0 = 3000 counts/s / (0.25 detection efficiency) = 12000 nucleiThe number of radioactive nuclei at time t = 2 min is:N = N0 * (1/2)^(t/t1/2) = 12000 * (1/2)^(2/2) = 3000 nuclei

A Radioactive Source Has a Half-Life of 2 Min