1. What is the percent activity of a radioactive sample (relative to its original activity) that has undergone four half-lives of decay?
a. 6.25 percent
b. 25 percent
c. 12.5 percent
d. 3.13 percent
e. 75.0 percent
2. Iodine-131, which is used to treat thyroid cancer, has a half-life of 8.04 days. How much time is required for 68 percent of the isotope to decay?
a. 13 days
b. 7 days
c. 43 days
d. 53 days
e. 4 days
Chemistry Quiz! 10 points for BA?
2018-04-07 9:14 am
回答 (2)
2018-04-07 1:52 pm
✔ 最佳答案
1.After 4 half-lives of decay, remained activity
= (1/2)⁴
= 1/16
= (1/16) × 100%
= 6.25%
The answer: a. 6.25 percent
====
2.
Let n be the number of half-lives.
Fraction remained :
(1/2)ⁿ = 100% - 68%
log(1/2)ⁿ = log(0.32)
n log(0.5) = log(0.32)
n = log(0.32)/log(0.5)
Time taken = (8.04 days) × [log(0.32)/log(0.5)] = 13 days
The answer : a. 13 days
2018-04-07 9:24 am
1 half life - 50%
2 half lives - 25%
3 half lives - 12.5 %
4 half lives - 6.25 %
As for the second answer - a wild SWAG is 4 days. a, c and d are clearly wrong. But A = Ao(1/2)^0.68 will give you the exact answer
2 half lives - 25%
3 half lives - 12.5 %
4 half lives - 6.25 %
As for the second answer - a wild SWAG is 4 days. a, c and d are clearly wrong. But A = Ao(1/2)^0.68 will give you the exact answer
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