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Half-lifeIB MYP Physics: Flashcards

What these 13 flashcards ask

  • Define half-life.
  • What is activity, and what is its unit?
  • How do you find the number of half-lives that have passed?
  • What fraction of a sample is left after 3 half-lives?
  • A sample has an activity of 640 Bq and a half-life of 2 hours. What is the activity after 6 hours?
  • Does a radioactive sample reach zero activity after two half-lives?
  • How do you find half-life from a decay curve?
  • Why is a short half-life suitable for a medical tracer?
  • Why is gamma radiation used in medical tracers?
  • Why does a smoke alarm source need a long half-life?
  • Which type of radiation is used in smoke alarms?
  • What is the half-life of carbon-14, and what is it used for?
  • Why is a long half-life needed for a thickness gauge source?

Exam questions on Half-life

  1. A hospital in Singapore uses technetium-99m as a medical tracer. Its half-life is 6 hours. A sample is delivered at 08:00 with an activity of 400 MBq (megabecquerels).
    Calculate the activity of the sample at 14:00 on the following day.2 marks
  2. A student measures the corrected count rate (background already subtracted) from a radioactive sample over 40 minutes. At 0 minutes the count rate is 160 counts per second. At 10 minutes it is 80 counts per second, at 20 minutes it is 40 counts per second, at 30 minutes it is 20 counts per second and at 40 minutes it is 10 counts per second.
    Describe the pattern shown by the count rate, using the data to support your answer.2 marks
  3. A company is choosing a radioactive isotope for two jobs: as a medical tracer injected into a patient's blood, and as the radiation source in a smoke alarm. Isotope P has a half-life of 6 hours and emits gamma rays. Isotope R has a half-life of 432 years and emits alpha particles.
    Identify which isotope should be used as the medical tracer and explain your choice.3 marks
See the full worksheet

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).