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Radioactive isotopes often occur together in mixtures. Suppose a 390g sample con

ID: 1299715 • Letter: R

Question

Radioactive isotopes often occur together in mixtures. Suppose a 390g sample contains 131Ba, with a half-life of 12 days, and 47Ca, with a half-life of 4.5 days.

If there are initially twice as many calcium atoms as there are barium atoms, what will be the ratio of calcium atoms to barium atoms 3.30 weeks later?

Radioactive isotopes often occur together in mixtures. Suppose a 390g sample contains 131Ba, with a half-life of 12 days, and 47Ca, with a half-life of 4.5 days. If there are initially twice as many calcium atoms as there are barium atoms, what will be the ratio of calcium atoms to barium atoms 3.30 weeks later? NCa/NBa = ?

Explanation / Answer

compute the remaining fractions and take their ratio.
Ca(0)/Ba(0) = 2

as 3.30 week =23 days
Ba(t)/Ba(0) = 2^(-23/12) = 0.264865
Ca(t)/Ca(0) = 2^(-23/4.5) = 0.0289335
Ca(t)/Ba(t) = Ca(0)/Ba(0) * (Ca(t)/Ca(0)) / (Ba(t)/Ba(0)) = 0.21847