Decay & Transformations (Edexcel GCSE Physics)

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Nuclear Transformations

  • During radioactive decay, the atomic (proton) number and mass (nucleon) number of the nuclei will change

Alpha Emission

  • An alpha particle consists of 2 protons and 2 neutrons (same as a helium nucleus)
  • It is emitted from large unstable nuclei

Alpha particle, downloadable AS & A Level Physics revision notes

Nuclear notation for an alpha particle

  • When an alpha particle is emitted from a nucleus:
    • The nucleus loses 2 protons
      • The atomic (proton) number decreases by 2

    • The nucleus loses 4 particles (nucleons) in total
      • The mass (nucleon) number decreases by 4

Beta emission

Beta particle, downloadable AS & A Level Physics revision notes

Nuclear notation for beta minus and beta plus particle

  • Beta minus decay is when a neutron turns into a proton emitting an electron
  • When a beta minus particle is emitted from a nucleus:
    • The number of protons in the nucleus increases by 1
      • The atomic (proton) number increases by 1

    • The total number of particles in the nucleus remains the same
      • The mass (nucleon) number does not change

  • Beta plus decay is when a proton turns into a neutron emitting a positron
  • When a beta plus particle is emitted from a nucleus:
    • The number of protons in the nucleus decreases by 1
      • The atomic (proton) number decreases by 1

    • The total number of particles in the nucleus remains the same
      • The mass (nucleon) number does not change

Gamma Emission

Gamma particle, downloadable AS & A Level Physics revision notes

Nuclear notation for a gamma particle

  • Gamma waves are emitted from a nucleus when the nucleus needs to lose some energy
  • This usually occurs because the nucleus has excess energy following a previous decay
  • Therefore, no protons or neutrons are lost from the nucleus in this process
    • The atomic (proton) and mass (nucleon) numbers do not change

 Neutron Emission

  • A small number of isotopes can decay by emitting neutrons
  • When a nucleus emits a neutron:
    • The number of protons does not change
      • The atomic (proton) number does not change

    • The total number of particles (nucleons) in the nucleus decreases by 1
      • The mass (nucleon) number decreases by 1

Worked example

A nucleus with 11 protons and 13 neutrons undergoes beta minus decay. It forms magnesium, which has the element symbol Mg.Worked example beta decay, downloadable IGCSE & GCSE Physics revision notesWhich is the correct isotope of magnesium formed during the decay?

ANSWER:  D

Step 1: Calculate the mass number of the original nucleus

    • The mass number is equal to the number of protons plus the number of neutrons
    • The original nucleus has 11 protons and 13 neutrons

11 + 13 = 24

    • The mass number of the original nucleus is 24

Step 2: Calculate the new atomic number

    • During beta decay a neutron changes into a proton and an electron
    • The electron is emitted as a beta particle
    • The neutron has an atomic number of 0 and the proton has an atomic number of 1
    • So the atomic number increases by 1

11 + 1 = 12

    • The new nucleus has an atomic number of 12

Step 3: Calculate the new mass number

    • Protons and neutrons both have a mass number of 1
    • Changing a neutron to a proton will not affect the mass number
    • The new nucleus has a mass number of 24 (the same as before)

Gamma Emission

  • Nuclei that have undergone radioactive decay often undergo nuclear rearrangement with a loss of energy as gamma radiation rather than a change in the atomic structure
  • A gamma ray emitted has high energy but there is no change to the mass or charge of the initial atom
    • This is because gamma rays are electromagnetic radiation that have 0 atomic and mass number

Gamma decay, downloadable IGCSE & GCSE Physics revision notes

Atom emitting high energy gamma radiation

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.