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5. Nuclear physics

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  1. 5.1.1 The atom

    1. • Describe the structure of an atom in terms of a positively charged nucleus and negatively charged electrons in orbit around the nucleus

    2. • Know how atoms may form positive ions by losing electrons or form negative ions by gaining electrons

    3. • Describe how alpha-particle scattering by thin metal supports the nuclear atom: (a) tiny nucleus with mostly empty space around it (b) nucleus contains most atomic mass (c) nucleus is positively charged

  2. 5.1.2 The nucleus

    1. • Describe the composition of the nucleus in terms of protons and neutrons

    2. • State the relative charges of protons, neutrons and electrons as +1, 0 and –1 respectively

    3. • Define the terms proton number (atomic number) Z and nucleon number (mass number) A and be able to calculate the number of neutrons in a nucleus

    4. • Use the nuclide notation A ZX

    5. • Explain what is meant by an isotope and state that an element may have more than one isotope

    6. • Describe the processes of nuclear fission and nuclear fusion as the splitting or joining of nuclei, to include the nuclide equation and qualitative description of mass and energy changes without values

    7. • Know the relationship between the proton number and the relative charge on a nucleus

    8. • Know the relationship between the nucleon number and the relative mass of a nucleus

  3. 5.2.1 Detection of radioactivity

    1. • Know what is meant by background radiation

    2. • Know the sources that make a significant contribution to background radiation including: (a) radon gas (in the air) (b) rocks and buildings (c) food and drink (d) cosmic rays

    3. • Know: ionising nuclear radiation can be measured using a detector connected to a counter

    4. • Use count rate measured in counts/s or counts/minute

    5. • Use measurements of background radiation to determine a corrected count rate

  4. 5.2.2 The three types of nuclear emission

    1. • Describe the emission of radiation from a nucleus as spontaneous and random in direction

    2. • Identify alpha (α), beta (β) and gamma (γ) emissions from the nucleus by recalling: (a) their nature (b) their relative ionising effects (c) their relative penetrating abilities (β+ are not included, β-particles will be taken to refer to β–)

    3. • Describe the deflection of α-particles, β-particles and γ-radiation in electric fields and magnetic fields

    4. • Explain their relative ionising effects with reference to: (a) kinetic energy (b) electric charge

  5. 5.2.3 Radioactive decay

    1. 5.2.3.1Radioactive decay is a change in an

      • Know: radioactive decay is a change in an unstable nucleus that can result in the emission of α-particles or β-particles and/or γ-radiation; know: these changes are spontaneous and random

    2. 5.2.3.2During α-decay or β-decay, the nucleus

      • State: during α-decay or β-decay, the nucleus changes to that of a different element

    3. 5.2.3.3Isotopes of an element may be

      • Know: isotopes of an element may be radioactive due to an excess of neutrons in the nucleus and/or the nucleus being too heavy

    4. 5.2.3.4Effect of α-decay, β-decay and

      • Describe the effect of α-decay, β-decay and γ-emissions on the nucleus, including an increase in stability and a reduction in the number of excess neutrons; the following change in the nucleus occurs during β-emission neutron → proton + electron

    5. 5.2.3.5Decay equations, using nuclide

      • Use decay equations, using nuclide notation, to show the emission of α-particles, β-particles and γ-radiation

  6. 5.2.4 Half-life

    1. • Define half-life as the time for half the nuclei in any sample to decay; use it in simple calculations with tables or decay curves, excluding background radiation

    2. • Calculate half-life from data or decay curves from which background radiation has not been subtracted

    3. • Explain isotope choice using radiation type and half-life for: (a) smoke alarms (b) food irradiation (c) gamma sterilisation of equipment (d) material thickness control linked to penetration/absorption (e) cancer diagnosis/treatment using gamma rays

  7. 5.2.5 Safety precautions

    1. • State the effects of ionising nuclear radiations on living things, including cell death, mutations and cancer

    2. • Describe how radioactive materials are moved, used and stored in a safe way

    3. • Explain safety precautions for all ionising radiation in terms of reducing exposure time, increasing distance between source and living tissue and using shielding to absorb radiation