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Question
(a) Background radiation due to ${}^{226}\textrm{Ra}$ averages only 0.01 mSv/y, but it can range upward depending on where a person lives. Find the mass of ${}^{226}\textrm{Ra}$ in the 80.0-kg body of a man who receives a dose of 2.50-mSv/y from it, noting that each ${}^{226}\textrm{Ra}$ decay emits a 4.80-MeV $\alpha$ particle. You may neglect dose due to daughters and assume a constant amount, evenly distributed due to balanced ingestion and bodily elimination. (b) Is it surprising that such a small mass could cause a measurable radiation dose? Explain.
1. $11.3 \textrm{ ng}$
2. Yes, this mass is imperceptibly small. It has an outsized effect due to the relative biological effectiveness of the type of radiation, namely alpha particles.
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