CAIE A-Level Physics A2 23.2.6 The Exponential Nature of Radioactive Decay and Sketch and Use the

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Iodine-131 $\left({ }_{53}^{131} \mathrm{I}\right)$ is a radioactive isotope with a decay constant of $9.9 \times 10^{-7} \mathrm{~s}^{-1}$ .

Regulations require that the activity of iodine-131 in 1.0 kg of water is to be less than 170 Bq .

Calculate the time, in days, for the activity of the contaminated water in (b) to be reduced to 170 Bq .

time =

days

$\begin{aligned} A=A_{0} \mathrm{e}^{-\lambda t} 170=560 \exp \left(-9.9 \times 10^{-7} \times t\right) \end{aligned}$ $t=1.2 \times 10^{6} \mathrm{~s}$
= 14 days

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CAIE A-Level Physics A2 23.2.6 The Exponential Nature of Radioactive Decay and Sketch and Use the Topic Practice

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