PhysicsChapter 8: Nuclear Physics
Mass Defect
Mass defect
Definition
Mass defect is the difference between the total mass of the separate nucleons of a nucleus and the actual mass of the bound nucleus.
Atomic-Mass Form
A nucleus consists of: `Z` protons `N` neutrons where: A = Z + N If the individual nucleons were separated, their total mass would be: Zmₚ + Nmₙ But the measured mass of the bound nucleus is smaller. Therefore: Δm = Zmₚ + Nmₙ − Mnucleus This difference is called the mass defect. It occurs because energy is released when nucleons combine to form a bound nucleus. According to Einstein's mass-energy relation: E = mc² the released binding energy corresponds to a reduction in mass. When atomic masses are used, electron masses must be handled consistently. A convenient relation is: **Δm = ZmH + Nmₙ − Matom** where `m_H` is the mass of a hydrogen atom.
Formula / Key Relation
**Δm = Zmₚ + Nmₙ − Mnucleus and: E = Δmc²**
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Mass Defect
- Separate nucleons mass
- − actual nucleus mass
- = 0
- `E = Δmc²`
60-second revision
- Mass defect is the mass equivalent of nuclear binding energy.
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