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Radioactivity

Background radiation and detecting radioactivity

  • 3 things to know
  • Paper 5

Overview

Background radiation and correcting count rates for it, natural sources such as radon, rocks, food and cosmic rays, sources from human activity, doses for aircraft crew, and detecting radiation with photographic film, film badges and Geiger–Müller tubes.

What you need to know

Answer each one before you reveal it.

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Key term

What is meant by background radiation?

Key term

Why does the level of background radiation differ from one place to another?

Key term

Name three natural sources of background radiation that originate on Earth.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by background radiation?

    Model answer

    Background radiation is the low level of ionising radiation that is around us all the time.

  2. 2

    Why must background radiation be measured before an experiment with a radioactive source?

    Model answer

    Its count rate has to be subtracted so that only the radiation from the source is counted.

  3. 3

    A detector records 540 counts per minute near a source, and 25 counts per minute when the source is taken away. What is the corrected count rate for the source?

    Model answer

    The corrected count rate is 515 counts per minute.

  4. 4

    Does background radiation come mainly from human activity?

    Model answer

    No, by far the largest part of it comes from natural sources.

  5. 5

    Why does the level of background radiation differ from one place to another?

    Model answer

    The rock underground differs, and some rocks release far more radon gas than others.

  6. 6

    Which natural gas released from the ground is the largest single contributor to background radiation?

    Model answer

    Radon gas.

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