Complete notes for Chapter 12 Nuclear and Particle Physics. Covers Radioactivity, Fundamental Forces, Standard Model, Quarks, Leptons, and Nuclear Reactions.
Composition: The nucleus consists of protons and neutrons (collectively called nucleons). Atomic number Z is the number of protons. Mass number A is the total number of nucleons (A = Z + N).
Isotopes: Atoms of the same element (same Z) but different number of neutrons (different A).
1. Strong Nuclear Force: Strongest force, short range (~10⁻¹⁵ m). Holds quarks together in hadrons and nucleons in the nucleus. Mediated by Gluons.
2. Electromagnetic Force: Acts between charged particles. Infinite range. Mediated by Photons.
3. Weak Nuclear Force: Responsible for radioactive decay (beta decay). Short range. Mediated by W and Z bosons.
4. Gravitational Force: Weakest force, infinite range. Acts on mass/energy. Mediated by Gravitons (hypothetical).
Alpha Decay (α): Emission of Helium nucleus (2p, 2n). A decreases by 4, Z decreases by 2. High ionization, low penetration.
Beta Decay (β):
β⁻: Neutron turns into proton + electron + anti-neutrino.
β⁺: Proton turns into neutron + positron + neutrino.
Moderate ionization and penetration.
Gamma Decay (γ): Emission of high-energy photons. No change in A or Z. Low ionization, high penetration.
Fermions (Matter):
Quarks: Up, Down, Charm, Strange, Top, Bottom. Combine to form Hadrons (Baryons like p, n and Mesons like π, K).
Leptons: Electron, Muon, Tau and their neutrinos. Fundamental particles.
Bosons (Force Carriers): Photon (EM), Gluon (Strong), W/Z (Weak), Graviton (Gravity), Higgs Boson (Mass).
Every particle has an anti-particle with same mass but opposite charge (e.g., Electron & Positron). When they meet, they annihilate, converting mass to energy (Pair Annihilation). Conversely, energy can create matter-antimatter pairs (Pair Production, requiring E ≥ 1.02 MeV).
Proton: uud (2 Up + 1 Down). Charge: +2/3 + 2/3 - 1/3 = +1.
Neutron: udd (1 Up + 2 Down). Charge: +2/3 - 1/3 - 1/3 = 0.