Decay & Transformations (Edexcel GCSE Physics: Combined Science)

• 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

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

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

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

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)

• 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

Atom emitting high energy gamma radiation