Calculating Half Life

What is Half-life?

• The amount of time it takes for some of the nuclei in a sample of the isotope to decay

• The amount of time it takes for half the electrons in a sample of the isotope to decay

• The amount of time it takes for half the nuclei in a sample of the isotope to decay

• the amount of time it takes to double the nuclei in a sample of the isotope to decay

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NGSS.HS-PS1-8

Actinium-226 has a half-life of 29 hours. If 100 mg of actinium-226 disintegrates over a period of 58 hours, how many mg of actinium-226 will remain?

• 50 mg

• 25 mg

• 12.5 mg

• 6.25 mg

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NGSS.HS-PS1-8

If one-fourth of the carbon-14 is remaining then how many half-lives have passed?

• 1

• 2

• 3

• 4

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NGSS.HS-PS1-8

What is the half-life of iodine-131?

• 32 days

• 8 days

• 16 days

• 24 days

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What is the half-life of this isotope?

• 3 days

• 5 days

• 8 days

• 10 days

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NGSS.HS-PS1-8

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

• 1/2

• 1/3

• 1/16

• 1/8

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NGSS.HS-PS1-8

The % of the isotope remaining after 1 Half Life.

• 50%

• 25%

• 12.5%

• 6.25%

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NGSS.HS-PS1-8

The % of the parent isotope remaining after 2 Half Lives.

• 50%

• 25%

• 12.5%

• 6.25%

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NGSS.HS-PS1-8

After the 5th half-life, how much of the sample is left?

• 3.125%

• 1/3

• 1/16

• 12.4%

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NGSS.HS-PS1-8

What is the count rate after 60 days for a radioactive isotope with a half-life of 20 days and an initial count rate of 1000 counts per second?

• 500 counts per second

• 250 counts per second

• 125 counts per second

• 62.5 counts per second

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NGSS.HS-PS1-8