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

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First teaching 2023

First exams 2025

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Nuclear Equations (CIE A Level Physics)

Revision Note

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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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