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1. At 8:00 a.m., a patient receives a 58-mg dose of I -131 to obtain an image of her thyroid. If the nuclide has a half-life of 8 days, what mass of the nuclide remains in the patient at 5:00 p.m. the next day? (Assume no excretion of the nuclide from the body).

2. A radioactive sample contains 1.55g of an isotope with a half-life of 3.8 days. What mass of the isotope will remain after 5.5 days? (Assume no excretion of the nuclide from the body.) Express your answer using two significant figures.

3. A particular smoke detector contains 1.45Î¼Ci of 241 Am, with a half-life of 458 years. The isotope is encased in a thin aluminum container. Calculate the mass of 241 Am in grams in the detector. Express your answer numerically in grams.

4. The following conversion factors may help you when working this problem:
Activity in becquerels (Bq ) = activity in disintegrations per second (dps).

1.00 mCi=3.70Ã—10 7 Bq. Neutron activation analysis for a sample of a rock revealed the presence of 59 26 Fe, which has a half-life of 46.3days. Assuming the isotope was freshly separated from its decay products, what is the mass of 59 26 Fe in a sample emitting 1.00 mCi of radiation? Express your answer in grams to three significant figures.

#### Solution Preview

1. A = Ao x e^-(0.693t/t1/2) = 58 x e^-(0.693 x 33/(8 x 24)) = 51 mg

2. A = Ao x e^-(0.693t/t1/2) = ...