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Nuclear Radiation

Mass deficit, binding energy and the atomic mass unit

  • 2 things to know
  • Papers 2 and 3

Overview

Recall questions on binding energy and mass deficit, why a nucleus is lighter than its nucleons, ΔE = c²Δm, and the atomic mass unit in SI units, joules and MeV.

What you need to know

Answer each one before you reveal it.

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Numbers

What equation links a change in energy to a change in mass, what value of c is used, and what is the atomic mass unit?

Numbers

What is the atomic mass unit in SI units, and how is binding energy per nucleon calculated for helium-4?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by the binding energy of a nucleus?

    Model answer

    It is the energy that must be supplied to separate a nucleus completely into its individual protons and neutrons.

  2. 2

    What is the mass deficit of a nucleus?

    Model answer

    It is the difference between the total mass of the separate nucleons and the mass of the assembled nucleus.

  3. 3

    Why is a nucleus always less massive than the nucleons it is made from?

    Model answer

    Energy is released when the nucleons bind together, and that release of energy corresponds to a loss of mass through ΔE = c²Δm.

  4. 4

    State the equation linking a change in energy to the associated change in mass:

    Model answer

    ΔE = c²Δm, where c is the speed of light in a vacuum.

  5. 5

    What value of the speed of light should be used in mass–energy calculations?

    Model answer

    The speed of light in a vacuum is 3.00 × 10⁸ m s⁻¹.

  6. 6

    How is the atomic mass unit defined?

    Model answer

    One atomic mass unit is one twelfth of the mass of a neutral atom of carbon-12.

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