Half-Life Quiz
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5 questions, one answer each
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1. Which of these is a source of background radiation?
- A. A hospital X-ray machine
- B. Radon gas in the air
- C. A nuclear power station accident
- D. A smoke alarm
2. How do you find the corrected count rate of a radioactive sample?
- A. Add the background count rate to the measured count rate
- B. Subtract the background count rate from the measured count rate
- C. Multiply the measured count rate by the half-life
- D. Divide the measured count rate by two
3. What is the half-life of a radioactive isotope?
- A. The total time for all the nuclei in a sample to decay
- B. The time taken for half the nuclei in a sample to decay
- C. The time taken for a sample to become non-radioactive
- D. The average lifetime of a single nucleus
4. A source's corrected count rate falls from 1200 counts/minute to 150 counts/minute over 30 minutes. How many half-lives have passed, and what is the half-life of the isotope?
- A. 4 half-lives; half-life is 7.5 minutes
- B. 3 half-lives; half-life is 10 minutes
- C. 2 half-lives; half-life is 15 minutes
- D. 3 half-lives; half-life is 30 minutes
5. A company needs an isotope for a permanent thickness gauge on a production line and another isotope for a medical scan that must clear the patient's body quickly. Explain how half-life requirements differ between these two uses.
- A. Both need the shortest possible half-life to minimise cost
- B. The thickness gauge needs a short half-life so it stops working quickly; the medical scan needs a long half-life to stay active in the body
- C. The thickness gauge needs a long half-life so its output stays constant over years of use; the medical scan needs a short half-life to minimise the patient's radiation exposure
- D. Half-life is irrelevant to both applications; only radiation type matters