Half Life Calculations

After 3 half-lives, what fraction of the original amount of a radioactive substance remains?

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NGSS.HS-PS1-8

What is the half-life of a substance if 100 grams of it decays to 25 grams in 8 years?

• 2 years

• 4 years

• 8 years

• 16 years

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NGSS.HS-PS1-8

A radioactive element decays to one-eighth of its original amount after 24 years. What is its half-life?

• 6 years

• 8 years

• 12 years

• 24 years

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NGSS.HS-PS1-8

If a sample of a radioactive isotope has an initial mass of 20 grams and a half-life of 10 years, how much of the isotope will remain after 20 years?

• 10 grams

• 5 grams

• 15 grams

• 2.5 grams

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NGSS.HS-PS1-8

The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams would be left after 7.2 minutes has elapsed?

• 100.0g

• 50.0g

• 12.5g

• 8.5g

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NGSS.HS-PS1-8

If the half-life of uranium-232 is 70 years, how many half-lives will it take for 10 g of it to be reduced to 1.25 g?

• half-life

• half-lives

• half-lives

• half-lives

Tags

NGSS.HS-PS1-8

Geologist use the time it takes for a radioactive isotope to decay to half its original mass called a___________.

• radioactive decay

• isotope

• half-life

• carbon dating

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NGSS.HS-PS1-8

If 10 mg of iodine 131 is given to a patient, how much is left after 24 days? The half-life of iodine-131 is 8 days.

• 25mg

• 25g

• 10g

• 10mg

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NGSS.HS-PS1-8

After the third half-life, how much of the sample is left?

• 1/2

• 1/3

• 1/16

• 1/8

Fermium-253 has a half-life of 0.334 seconds. A radioactive sample is considered to be completely decayed after 10 half-lives. How much time will elapse for this sample to be considered gone?

• 0.334 seconds

• 3.34 seconds

• 1.77 seconds

• 13.4 seconds

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NGSS.HS-PS1-8