Radioactivity

    OCR
    GCSE

    Radioactivity is the random process by which unstable atomic nuclei decay to become more stable by emitting ionizing radiation in the form of alpha particles, beta particles, or gamma rays. Candidates must characterize these emissions by their penetrating power, ionizing ability, and range in air, while applying conservation laws to balance nuclear decay equations. The topic requires mathematical modelling of radioactive decay using the concept of half-life to predict activity levels over time. Furthermore, a critical distinction must be drawn between irradiation and contamination to evaluate safety protocols in industrial and medical contexts.

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    Objectives
    4
    Exam Tips
    4
    Pitfalls
    5
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for defining half-life as the time taken for the number of nuclei of the isotope in a sample to halve
    • Credit responses that identify an alpha particle as a helium nucleus (2 protons and 2 neutrons)
    • Award 1 mark for balancing nuclear equations where the sum of mass numbers and atomic numbers is conserved on both sides
    • Credit the explanation that beta decay involves a neutron turning into a proton and an electron within the nucleus
    • Award 1 mark for stating that irradiation does not cause the object to become radioactive, whereas contamination involves the presence of radioactive atoms on/in the material

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the type of radiation, but you need to be more specific about *why* it has that penetrating power"
    • "Check your nuclear equation balancing — remember that a beta particle has an atomic number of -1"
    • "Good definition of half-life, but ensure you apply it correctly to the graph provided by drawing lines to the axes"
    • "You have confused irradiation with contamination; remember that irradiation is exposure to waves/particles, while contamination is the physical presence of the source"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for defining half-life as the time taken for the number of nuclei of the isotope in a sample to halve
    • Credit responses that identify an alpha particle as a helium nucleus (2 protons and 2 neutrons)
    • Award 1 mark for balancing nuclear equations where the sum of mass numbers and atomic numbers is conserved on both sides
    • Credit the explanation that beta decay involves a neutron turning into a proton and an electron within the nucleus
    • Award 1 mark for stating that irradiation does not cause the object to become radioactive, whereas contamination involves the presence of radioactive atoms on/in the material

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When using a graph to determine half-life, always draw construction lines on the graph to show your working; examiners look for this evidence
    • 💡For 6-mark questions on safety, structure your answer by source type: specify the shielding (e.g., lead), the distance (e.g., tongs), and the exposure time
    • 💡Memorise the specific penetrating powers and ionizing abilities of alpha, beta, and gamma radiation, as these are often required for 'Compare' questions
    • 💡In nuclear equations, double-check that the top numbers (mass) and bottom numbers (charge) sum to the same value on both sides of the arrow

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing 'irradiation' with 'contamination' — students frequently state that being exposed to radiation makes an object radioactive
    • Incorrectly calculating half-life by dividing the total time by the number of nuclei, rather than using the graph to find the time interval for activity to halve
    • In beta decay equations, students often forget that the atomic number increases by 1, or they change the mass number
    • Describing radioactive decay as a process that can be influenced by external factors (temperature, pressure) rather than stating it is random and spontaneous

    Key Terminology

    Essential terms to know

    Atomic structure, isotopes, and nuclear stability
    Properties and identification of alpha, beta, and gamma radiation
    Nuclear decay equations and conservation of mass/charge
    Activity, count-rate, and half-life calculations
    Hazards and prevention: Irradiation vs. Contamination

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Describe
    Explain
    State
    Suggest
    Compare

    Practical Links

    Related required practicals

    • •{"code":"Modelling Decay","title":"Simulation of radioactive decay","relevance":"Using dice or coins to model the random nature of decay and half-life curves"}

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