8 original questions from New Regents. The worksheet, answer key, and browser practice are free.
Half-Life from Data 4 questions
Half-Life from Data
New Regents original practice • Name: ____________________ Date: __________ Show your work for written answers.
A half-life is the time for half the radioactive nuclei in a large sample to decay. Use the fraction of the original sample remaining after each interval.
Question 1
A sample initially has 600 radioactive nuclei. About how many remain after one half-life?
- 150
- 200
- 300
- 600
Question 2
A radioactive sample begins with 80.0 mg of its parent isotope. How much parent isotope remains after two half-lives? Show your work.
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Question 3
What fraction of the original radioactive nuclei remains after three half-lives?
- 1/2
- 1/3
- 1/6
- 1/8
Question 4
Explain why knowing the half-life does not tell you when a particular radioactive nucleus will decay.
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Tracking a Model Isotope 4 questions
Tracking a Model Isotope
Use the information below to answer the questions.
A simulation records the number of undecayed parent nuclei in a model sample. The table gives the expected counts for this isotope.
| Time (h) | Undecayed nuclei |
|---|---|
| 0 | 1,600 |
| 6 | 800 |
| 12 | 400 |
| 18 | 200 |
Question 5
What is the half-life of the modeled isotope?
- 3 h
- 6 h
- 12 h
- 18 h
Question 6
Predict the number of undecayed nuclei after 24 hours. Use the data to show your reasoning.
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Question 7
How many of the original nuclei have decayed after 12 hours in this model?
- 200
- 400
- 800
- 1,200
Question 8
A second sample of the same isotope starts with twice as many parent nuclei. Explain how its half-life and expected count after 6 hours compare with the first sample.
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