1. After a sudden release of radioactivity from the Chernobyl nuclear reactor ac
ID: 1788096 • Letter: 1
Question
1. After a sudden release of radioactivity from the Chernobyl nuclear reactor accident in 1986, the radioactivity of milk in Poland rose to 2 000 Bq/L due to iodine-131 present in grass eaten by dairy cattle. Radioactive iodine, with half-life 8.0 days, is particularly hazardous because the thyroid gland concentrates iodine.
What is the storage time needed to decrease iodine-131 content of cheese produced from these cows’ milk to 15% of the original level?
2. In the 1950s, radioactive material was spread over the land from above-ground nuclear tests. A woman drinks some contaminated milk and ingests 0.0500 g of strontium-90 (half-life 29 years),
which is taken up by bones and teeth and not eliminated.
a. How much strontium-90 is present in her body after 10 years?
b. How long will it take for 99.9% of the strontium-90 to decay?
3. Radioactive isotope iodine-131, with nuclear half-life of 8.1 days, is ingested by two people: one with healthy thyroid and the other with hyperactive thyroid. On two consecutive days, a counter positioned near the gland reads 10 000 and 9136 counts per seconds for the healthy person and 9500 and 7340 counts per seconds for the sick person. What are the biological half-lives of the isotope in the thyroids of the two people?
Explanation / Answer
1.
Given that,
Ao = 2 000 Bq/L
A = (15 / 100) * 2 000 Bq/L = 300 Bq/L
t1/2 = 8 days
Apply formula,
t = (t1/2 / 0.693) * ln(A / Ao)
t = (8 / 0.693) * ln (300 / 2000)
t = 21.9 days
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