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Chapter 12 — Chapter 12 — Nuclear and Particle Physics
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📘Easy summary
The nucleus contains protons and neutrons (nucleons). Atomic number Z = number of protons; mass number A = number of nucleons; neutron number N = A − Z; notation ᴬ_ZX. Isotopes are atoms of the same element with the same Z (same number of protons and electrons, same chemical properties) but different numbers of neutrons, hence different A, mass and nuclear stability. Nuclear masses are measured in atomic mass units (1 u = 931.5 MeV). The nucleus is held by the strong nuclear force acting between nucleons over very short range (~10⁻¹⁵ m).
⭐Key points
- A = Z + N.
- Isotopes: same Z, different N.
- 1 u = 931.5 MeV.
🔬Diagram
🌿Real-life example
⁸⁷₃₇Rb has 37 protons and 50 neutrons.
💡Exam tip
- Isotopes differ only in neutrons.
✅Quick check
1. Isotopes have the same:
2. Neutrons in ²³⁸₉₂U:
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