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A LevelPhysicsCIERevision Notes23. Nuclear Physics23.1 Mass Defect & Nuclear Binding EnergyNuclear Equations

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First exams 2025

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Nuclear Equations (CIE A Level Physics)

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Representing simple nuclear reactions

  • A nucleus can be described using straight X presubscript straight Z presuperscript straight A notation

AZX Notation, downloadable AS & A Level Physics revision notes

X presubscript Z presuperscript A notation is used to describe the constituents of a nucleus

  • The top number A represents the nucleon number or the mass number
    • Nucleon number (A) = total number of protons and neutrons in the nucleus
  • The lower number Z represents the proton or atomic number
    • Proton number (Z) = total number of protons in the nucleus

Worked example

When a neutron is captured by a uranium-235 nucleus, the outcome may be represented by the nuclear equation:

straight U presubscript 92 presuperscript 235 space plus space straight n presubscript 0 presuperscript 1 space rightwards arrow space Mo presubscript 42 presuperscript 95 space plus space La presubscript 57 presuperscript 139 space plus space x straight n presubscript 0 presuperscript 1 space plus space 7 straight e presubscript negative 1 end presubscript presuperscript 0

Determine the value of x.

Answer: 

Step 1: Balance the nucleon numbers (the top number)

235 + 1 = 95 + 139 + x(1) + 7(0)

Step 2: Rearrange to find the value of x

x = 235 + 1 − 95 − 139 = 2

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    Leander

    Author: Leander

    Expertise: Physics

    Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.