One of the dangers of radioactive fallout from a nuclear bomb is , which beta decays with a half-life of 29-y half-life. Because it has chemical properties much like calcium, the strontium, if eaten by a cow, becomes concentrated in its milk and ends up in the bones of whoever drinks the milk. The energetic decay electrons damage the bone marrow and thus impair the production of red blood cells. A 1- megaton bomb produces approximately 400 g of . Assuming that the fallout spreads uniformly over a area, we have to find the area that would have radioactivity equal to the allowed bone burden for one person of 0.002 mCi. The atomic mass of is 89.9 u.

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The atomic mass of is 89.9 u. A 1- megaton bomb produces approximately 400 g of . Therefore, the number of atoms in 400 g will be

Assuming that the fallout spreads uniformly over a area, the number of atoms per will be

The beta decay half-life of is 29 y. Therefore, its disintegration constant will be

We are given that the radioactivity equal to the allowed bone burden for one person is 0.002 mCi, or

Therefore, the element of area, , that will have the activity of 0.002 mCi will be given by