Nuclear Instability

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Nuclear Instability

Some isotopes of atoms are more stable than others. The unstable isotopes can decay radioactively.

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  • Above is a graph of the number of neutrons against the number of protons in an atom
  • There is a pattern where some atoms are more stable.
  • An unstable atom will decay to a more stable atom.
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Types of decay

  • Atoms usually decay through alpha or beta radiation untill they reach a stable point.
  • Any chain of alpha and beta radiation is possible to reach a stable point.
  • Alpha radiation reduces the atom by two neutrons and two protons.
  • Beta radiation reduced the atom by one neutron and increases by one proton.

Decay Equations

When an atom decays it may release radiation and a new atom is created. We can write equations for this decay.

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Types of radiation

  • Alpha radiation is made up of two protons and two neutrons.
    • The mass number will reduce by four and the atomic number by two.
  • Beta radiation changes a neutron into a proton and releases an electron.
    • The mass number will not change but the atomic number will increase by one.
  • Gamma radiation is a wave and will only change the energy of the atom, not the form
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Equations of decay

  • A decay equation shows the mass and atomic numbers for all of the atoms or radiation present.
  • Charge and mass must be conserved so we know that the sum of the mass number before and the sum after have to be the same.
  • We can work out what type of radiation is produced if we know the mass and atomic number before and after.
    • Remember radiation is a product, not a reactant. It should be after the arrow.

Excited States in Nuclei

Just as atoms have excited states, nuclei also have excited states.

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Atomic excited states

  • In an atom, an electron can gain energy and be promoted to a higher energy level.
  • When the electron returns to the original level, the energy is released as electromagnetic waves.
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Nuclear excited states

  • Nuclei also have excited states. This is because of the different arrangements of protons and neutrons within a nucleus.
  • When the protons and neutrons rearrange to a lower energy state, the excess energy is released as gamma radiation.
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  • It is possible to work out the energy of the gamma radiation released.
    • Technetium-99m is a valuable resource as it is used in gamma cameras in hospitals. It is produced from the beta decay of molybdenum-99.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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