Topic 11: Nuclear Radiation — Edexcel A-Level Physics
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Topic 11: Nuclear Radiation explained
Nuclear binding energy is the energy needed to separate a nucleus into its individual protons and neutrons, and it equals the mass deficit converted to energy.
Read the full explanation
The mass deficit Δm is the difference between the total mass of the separated nucleons and the mass of the bound nucleus; the bound nucleus is lighter. Use ΔE = c²Δm, with c = 3.00 × 10⁸ m s⁻¹, so c² = 9.00 × 10¹⁶ m² s⁻². Work in kilograms for mass to obtain joules, or convert to MeV using 1 u = 931.5 MeV or 1 eV = 1.60 × 10⁻¹⁹ J. For example, a mass deficit of 0.0300 u gives ΔE = 0.0300 × 931.5 ≈ 27.9 MeV. Binding energy per nucleon peaks near iron-56, explaining why fusion releases energy for light nuclei and fission releases energy for heavy nuclei.
Your focus
- Define nuclear binding energy and mass deficit.
- Use ΔE = c²Δm to calculate the energy released from a given mass deficit.
- Calculate and interpret binding energy per nucleon for a nucleus.
Topic 11: Nuclear Radiation exam tips
Marking Points
- Defines nuclear binding energy as the energy required to separate a nucleus into its constituent protons and neutrons.
- Defines the mass deficit as the difference between the mass of the separated nucleons and the mass of the bound nucleus.
- Applies ΔE = c²Δm correctly, using c = 3.00 × 10⁸ m s⁻¹ so that c² = 9.00 × 10¹⁶ m² s⁻².
- Converts between joules, electronvolts and atomic mass units using 1 eV = 1.60 × 10⁻¹⁹ J and 1 u = 931.5 MeV.
- Calculates binding energy per nucleon by dividing total binding energy by the nucleon number.
- Relates the peak in binding energy per nucleon near iron-56 to energy release in fusion and fission.
Examiner Tips
- 💡Write the equation ΔE = c²Δm and substitute values with units before calculating.
- 💡Convert atomic mass units to kilograms or to MeV consistently, and state which conversion you used.
- 💡Check the sign and direction of the mass deficit so the energy comes out positive.
Common Mistakes
- Using the mass of the bound nucleus minus the mass of separated nucleons and obtaining a negative deficit: the correction is to take the separated-nucleon mass minus the bound-nucleus mass so Δm is positive.
- Forgetting to square the speed of light: the correction is that the equation uses c², giving 9.00 × 10¹⁶ m² s⁻².
- Mixing units, for example using u for mass with c in m s⁻¹ without conversion: the correction is to convert mass to kilograms before using ΔE = c²Δm in joules.
- Reporting total binding energy when binding energy per nucleon is asked: the correction is to divide by the nucleon number.