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Half - Life Calculations
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Gravity
Definitions of alpha, beta and gamma radiation, decay equations and half-life definition and calculations. Fission and fusion definitions and an example.
Terms in this set (10)
The half-life of radon-222 is 3.8 days. How much of a 100. g sample is left after 15.2 days?
half-life = 3.8 days
total time of decay = 15.2 days
initial amount = 100. g
number of half-lives past: 15.2/3.8 = 4 half-lives
4 half-lives = 1/16 remains
100. g x 1/16 = 6.25 g
Carbon-14 has a half-life of 5,715 years. If a sample contains 70 mg originally, how much is left after 17,190 years?
half-life = 5,715 years
total time of decay = 17,190 years
initial amount = 70.0 mg
number of half-lives past: 17,190/5,715 = 3 half-lives
3 half-lives = 1/8 remains
100.mg x 1/8 = 12.5 mg
How much of a 500. g sample of potassium-42 is left after 62 hours? The half-life of potassium-42 is 12.4 hours.
half-life = 12.4 hours
total time of decay = 62.0 hours
initial amount = 500. g
number of half-lives past: 62.0/12.4 = 5 half-lives
5 half-lives = 1/32 remains
500. g x 1/32 = 15.625 g ~15.6 g
The half-life of cobalt-60 is 5.26 years. If 50.0 g are left after 15.8 years, how many grams were in the original sample?
half-life = 5.26 years
total time of decay = 15.8 years
final amount = 50.0 g
number of half-lives past: 15.8/5.26 = 3 half-lives
3 half-lives = 1/8 remains = 50.0 g
50.0 g x 8 = 400. g
If 100 g of gold-198 decays to 6.25 g in 10.8 days, what is the half-life of gold-198?
half-life = ? days
total time of decay = 10.8 days
initial amount = 100. g
final amount = 6.25 g
1/16 remains = 4 half-lives past
10.8 days/4 = 2.7 days = 1 half-life
What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 21.6 s?
7.2 s
All isotopes of technetium are radioactive, but they have widely varying half-lives. If an 800.0 g sample of technetium-99 to 100.0 g of technetium-99 in 639,000 y, what is its half-life?
213,000 years
A 208. g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 h. What is the half-life of this radioactive isotope?
15.0 h
If half-life of iodine-131 is 8.10 days, how long will it take a 50.00 g sample to decay to 6.25 g?
half-life = 8.10 days
total time of decay = ? days
initial amount = 50.00 g
final amount remaining = 6.25 g
1/8 remains = 3 half-lives
3 x 8.10 days = 24.3 days
The half-life of hafnium-156 is 0.025 s. How long will it take a 500. g sample to decay to ¼ its original mass?
half-life = 0.025 s
total time of decay = ? s
initial amount = 500 .g
1/4 remains = 2 half-lives
2 x 0.025 s = 0.05 s
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