AQA · GCSE · Physics

    Course version: 8463 · Version from Sept 2016

    The irradiated object does not become radioactive.

    Full specification wording

    Radioactive contamination: The irradiated object does not become radioactive.

    For the alpha, beta and gamma sources used at GCSE, irradiating an object does not make it radioactive.

    Checked against the AQA 8463 specification (opens in a new tab) on .

    • Point 5 of 8
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    For the alpha, beta and gamma sources used at GCSE, irradiating an object does not make it radioactive. Radiation passing through matter ionises atoms, knocking electrons out of them, but it leaves the nuclei unchanged. Radioactivity comes from unstable nuclei, so if no new unstable nuclei are created the object cannot become a source. As soon as the radioactive source is removed or shielded, the object emits nothing and can be handled safely. This is exactly why gamma irradiation is used to sterilise surgical instruments and food: the radiation kills bacteria as it passes through the sealed packet, then the contents are inert. Contamination is different, because there the source material itself is now sitting on or in the object.

    What earns the marks

    • The irradiated object not becoming a source of radiation itself.
    • The radiation ionising atoms by removing electrons while leaving the nuclei unchanged.
    • The object emitting nothing once the source is removed or shielded.
    • Applying this to sterilised food or instruments being safe to handle or eat afterwards.

    Common mistakes and how to put them right

    • Claiming irradiated food is radioactive and therefore dangerous to eat.

    • Saying some radiation is left behind, or soaks into, the irradiated object.

    • Concluding that irradiation is harmless to living tissue because nothing is transferred.

    • Confusing the ionisation of electrons with a change to the nucleus.

    • Using this statement to argue that a contaminated object is also not radioactive.

    Exam tips

    • Answer with the nucleus: saying the nuclei are unchanged is what earns the explanation mark rather than just repeating the statement.
    • Pair this point with contamination in comparison questions, because the contrast is what is being tested.
    • Use a worked example such as sterilised instruments to show the idea applied, not just stated.

    Try the lesson

    The start of the Radioactive contamination: The irradiated object does not become radioactive. lesson, made from checked teaching notes for this specification point.

    Have a go first

    What happens to an object that is irradiated?

    Listen

    For the alpha, beta and gamma sources used at GCSE, irradiating an object does not make it radioactive. Radiation passing through matter ionises atoms, knocking electrons out of them, but it leaves the nuclei unchanged. Radioactivity comes from unstable nuclei, so if no new unstable nuclei are created the object cannot become a source. As soon as the radioactive source is removed or shielded, the object emits nothing and can be handled safely. This is exactly why gamma irradiation is used to sterilise surgical instruments and food: the radiation kills bacteria as it passes through the sealed packet, then the contents are inert. Contamination is different, because there the source material itself is now sitting on or in the object. A strong answer earns marks for these points. the irradiated object not becoming a source of radiation itself. the radiation ionising atoms by removing electrons while leaving the nuclei unchanged. the object emitting nothing once the source is removed or shielded. applying this to sterilised food or instruments being safe to handle or eat afterwards. Exam tip: Answer with the nucleus: saying the nuclei are unchanged is what earns the explanation mark rather than just repeating the statement.

    See it

    A top-down flowchart. The first box reads 'Radiation passes through object' and points down to 'Atoms ionised: electrons knocked out', which points down to 'Nuclei left unchanged', then to 'No new unstable nuclei created', then to 'Object does not become radioactive'. From that box one arrow leads down to 'Source removed or shielded', which leads to 'Object emits nothing and is safe to handle'; another arrow leads to 'Example: gamma sterilised instruments and food'. A separate box reading 'Contamination: source material sits on or in object' is linked by a dotted arrow labelled 'different' to the 'Object does not become radioactive' box.
    Shows why an irradiated object does not become radioactive, from ionisation leaving nuclei unchanged through to the object emitting nothing once the source is removed, contrasted with contamination.

    Key words

    Say what each word means before you turn the card.

    irradiation leaves nuclei unchanged

    Try answering aloud or in your head before turning the card.

    ionisation of electrons

    Try answering aloud or in your head before turning the card.

    sterilisation

    Try answering aloud or in your head before turning the card.

    safe after removal

    Try answering aloud or in your head before turning the card.

    See every definition
    irradiation leaves nuclei unchanged
    Radiation passing through matter ionises atoms by knocking electrons out of them, but it leaves the nuclei unchanged, so the object does not become radioactive.
    ionisation of electrons
    Radiation passing through matter ionises atoms by knocking electrons out of them.
    sterilisation
    Gamma irradiation is used to sterilise surgical instruments and food because the radiation kills bacteria as it passes through the sealed packet.
    safe after removal
    As soon as the radioactive source is removed or shielded, the object emits nothing and can be handled safely.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The first box reads 'Radiation passes through object' and points down to 'Atoms ionised: electrons knocked out', which points down to 'Nuclei left unchanged', then to 'No new unstable nuclei created', then to 'Object does not become radioactive'. From that box one arrow leads down to 'Source removed or shielded', which leads to 'Object emits nothing and is safe to handle'; another arrow leads to 'Example: gamma sterilised instruments and food'. A separate box reading 'Contamination: source material sits on or in object' is linked by a dotted arrow labelled 'different' to the 'Object does not become radioactive' box.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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