Nuclear Physics
The science of atomic nuclei, radioactivity, and the strongest force in the universe.
๐ต Nuclear Structure
Atomic nuclei are composed of protons and neutrons (nucleons) held together by the strong nuclear force - the strongest of the four fundamental forces, acting at distances less than ~1 femtometer (10โปยนโต m).
โข๏ธ Radioactive Decay
Unstable nuclei spontaneously emit radiation: Alpha (ฮฑ) - helium nucleus; Beta (ฮฒ) - electron/positron; Gamma (ฮณ) - high-energy photon. Half-life (tยฝ) is the time for half the atoms to decay.
๐ฅ Nuclear Fission
A heavy nucleus (e.g., U-235) splits into lighter nuclei when struck by a neutron, releasing enormous energy plus more neutrons. This chain reaction powers nuclear reactors and weapons. E = ฮmcยฒ
โญ Nuclear Fusion
Light nuclei (e.g., deuterium + tritium) combine to form a heavier nucleus, releasing even more energy per unit mass than fission. Powers the Sun. ITER and NIF are the leading fusion research projects.
๐ Binding Energy
The energy required to completely separate a nucleus into its individual nucleons. Iron-56 has the highest binding energy per nucleon - making it the most stable nucleus. Energy is released when nuclei move toward iron-56.
๐ก๏ธ Chain Reaction
Each fission releases neutrons that can trigger further fissions. A controlled chain reaction (reactor) maintains k=1. An uncontrolled reaction (bomb) has k>1. Critical mass is the minimum mass to sustain a chain reaction.
๐งฒ Nuclear Forces
The strong force binds quarks into nucleons and nucleons into nuclei. The weak force governs beta decay and is responsible for nuclear transmutation. Both are short-range forces.
๐ฌ Isotopes
Atoms of the same element with different neutron numbers. U-235 (0.7% natural abundance) is fissile; U-238 (99.3%) is not. Enrichment increases the U-235 fraction for reactor or weapon use.