## Half-Life Answers

## 1. What is a becquerel?

## One decay per second

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## 2. What is the half-life of a radioactive isotope?

## The time that it takes for half of the parent nuclei to decay

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## 3. A substance has a half-life of 3 hours.

What fraction of the atoms will have decayed after 6 hours?

## 3/4 of the atoms will have decayed

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## 4. A radioactive substance activity falls from 8,000 counts per minute to 500 counts per minute in 20 hours. What is the half-life of the substance?

## 5 hours

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## 5. After the 3rd half-life, how much of the sample is left?

## 25% | 11/4 | 0.25

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## 6. After the second half-life, how much of the sample is left?

## 50% | 1/2 | 0.5

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## 7. What does the beta particle have a charge of?

## Minus 1

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## 8. If Carbon-14 has a half-life of 5,730 years, how old is a fossil if it has undergone 4 half-lives?

## 22,920 years old

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## 9. If Carbon-12 has a half-life of 5,730 years, how old is a fossil if it has undergone 7 half-lives?

## 40,110 years old

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## 10. An isotope has a half-life of 6 hours, what percentage of the isotope will be left after 24 hours?

## 6.25%

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