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Mass defect
Intermediate
Nuclear mass is less than the sum of the parts.
Δm = Zm_p+Nm_n−MThe mass of a nucleus is less than the sum of its separate nucleons: Δm = Zm_p + Nm_n − M. The missing mass is the binding energy.
Helium-4: Δm = 0.0304 u.
Use nuclear masses, not atomic masses, or correct for electrons.
In more detail
The mass defect is the difference between the mass of a nucleus and the sum of the masses of its separate nucleons. The missing mass corresponds to binding energy through E = mc².
Real-world uses
- Mass defect explains the energy released in nuclear reactions.
- It is used in calculations for fission and fusion energy.
- Nuclear physicists measure the mass defect to find out how much energy is released when a nucleus is assembled.
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Frequently asked questions
Why is the nucleus lighter than its parts?
Because binding energy is released when nucleons join, reducing the total mass.
Where does the mass go?
It becomes binding energy, which is a form of energy.
Why is the nucleus lighter than its parts?
Some of the mass is converted into binding energy when the nucleons are held together.
Related topics in Atomic & Nuclear Physics
Isotopes, isobars, isotones · Nuclear size · Nuclear density · Binding energy · Binding energy per nucleon · Nuclear force