Practice Problems
1) Fluorine-21 has a half life of
approximately 5 seconds. What fraction of the original nuclei would remain
after 1 minute?
2) Iodine-131 has a half life of 8 days. What
fraction of the original sample would remain at the end of 32 days?
3) The
half-life of chromium-51 is 28 days. If the sample contained 510 grams, how
much chromium would remain after 56 days? How much would remain after 1 year?
4) The half life of Uranium-238 is 4.5 billion
years and the age of earth is 4.5 X 109 years. What fraction of
Uranium-238 that was present when Earth was formed still remains?
5) A medical institution requests 1 g of
bismuth-214, which has a half life of 20 min. How many grams of bismuth-214
must be prepared if the shipping time is 2 h?
ANSWERS:
1) 1/4096 or 0.000244
2) 1/64 or 0.0156
3) 127.5 grams; 0.062 grams
4) 1/2 or 0.5
5) 64 grams
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