5.3.1: Practice Half-Life

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Exercise \(\PageIndex{1}\)

How many years does it take for 4.7 half-lives to pass for a sample of sodium-22? The half-life of sodium-22 is 2.6 years..

Answer: 12 years

Exercise \(\PageIndex{1}\)

How many half-lives have passed for a sample of gold-198 that is 3.4 weeks old? The half-life of gold-198 is 2.7 days.

Answer: 8.8 half-lives

Exercise \(\PageIndex{1}\)

If you start with 422 mg of calcium-47, how much will remain after 5.00 half-lives have passed?

Answer: 13.2 mg

Exercise \(\PageIndex{1}\)

The half-life of sodium-24 is 15.0 hours. If you begin with a sample that has 675 nCi of activity, what activity will remain after 3.75 days? (Hint: how many half-lives have passed for the sample after 3.75 days?)

Hint: 6.00 half-lives have passed.
Answer: 10.5 nCi of activity remain