Nuclear & Particle Physics — 60 Terms Defined

Alpha Decay Nuclear & Particle Physics MeV (Kinetic Energy) A radioactive decay process in which an unstable heavy nucleus emits an alpha particle (Helium-4 nucleus, ⁴₂He²⁺). ᴬ_Z X → ᴬ⁻⁴_(Z-2) Y + ⁴₂He (Q_alpha = E_kinetic)

Antimatter Nuclear & Particle Physics Energy (MeV / GeV) Subatomic material composed of antiparticles that share identical mass, spin, and lifetime as normal matter particles but possess opposite electric and quantum charges. e⁺ + e⁻ → 2 γ (511 keV gamma photons)

Atomic Nucleus Nuclear & Particle Physics fm (Femtometers = 10⁻¹⁵ m) The extremely dense, positively charged central core of an atom containing virtually all of its mass, composed of protons and neutrons bound by the strong nuclear force. R ≈ R₀ A^(1/3), R₀ ≈ 1.2 fm

Baryons Nuclear & Particle Physics Composite Fermion Class Subatomic composite hadrons made of three valence quarks held together by gluons, possessing half-integer spin (fermions). Quark Content: q q q, Spin = ½, ³/₂..., Baryon Number B = 1

Beta Decay Nuclear & Particle Physics MeV (Continuous Spectrum) A radioactive decay process mediated by the weak nuclear force in which a nucleus emits a beta particle (electron or positron) and a neutrino. β⁻: n → p + e⁻ + ν̄_e; β⁺: p → n + e⁺ + ν_e

Binding Energy per Nucleon Nuclear & Particle Physics MeV/nucleon The average energy required to remove a single proton or neutron from an atomic nucleus, representing relative nuclear stability. BE / A = Total Binding Energy / Mass Number

Breeder Reactor Nuclear & Particle Physics Breeding Ratio (Fissile Output / Input) A specialized nuclear reactor designed to generate more fissile nuclear fuel than it consumes during operation. ²³⁸₉₂U + ¹₀n → ²³⁹₉₂U → ²³⁹₉₃Np → ²³⁹₉₄Pu (Breeding Ratio > 1)

Cherenkov Radiation Nuclear & Particle Physics Blue Light Photons (~400 nm) The characteristic blue optical shockwave radiation emitted when a charged particle travels through a dielectric medium faster than the phase velocity of light in that medium. cos θ = c / (n v) = 1 / (n β)

Cloud Chamber Nuclear & Particle Physics Visual Particle Tracks A historic particle detector consisting of a sealed chamber containing supersaturated vapor where passing ionizing radiation forms visible condensation trails. Condensation droplets forming along ion trails

Control Rods Nuclear & Particle Physics Reactivity Control (pcm) Movable rods composed of high-neutron-capture elements (like cadmium, boron, or hafnium) inserted into a nuclear reactor core to regulate chain reaction rates. Neutron Capture Reaction: ¹⁰B + n → ⁷Li + α

Cosmic Rays Nuclear & Particle Physics eV or GeV (Particle Energy) High-energy relativistic atomic nuclei and subatomic particles originating from outer space that strike Earth's atmosphere. Primary Energies up to 10²⁰ eV (Extreme Relativistic Protons)

Coupling Constant Nuclear & Particle Physics Dimensionless Parameter A dimensionless number quantifying the relative interaction strength between particles or fields in a fundamental force interaction. α_EM = e² / (4π ε₀ ℏ c) ≈ 1 / 137, α_s(Q²)

Critical Mass Nuclear & Particle Physics kg (Kilograms) The minimum mass of fissile material required to sustain a continuous self-sustaining nuclear chain reaction. Neutron Leakage Rate = Neutron Production Rate (k = 1)

Cyclotron (Particle Physics) Nuclear & Particle Physics MeV (Beam Energy) A circular particle accelerator using a perpendicular magnetic field to bend charged particles into spiral paths while high-frequency AC electric fields accelerate them. f_c = (q B) / (2π m), KE_max = (q² B² R²) / (2 m)

Decay Constant Nuclear & Particle Physics s⁻¹ or years⁻¹ The probability per unit time that an individual radioactive nucleus will undergo spontaneous nuclear decay. λ = -(1 / N) (dN / dt) = ln(2) / t_½

Enriched Uranium Nuclear & Particle Physics Weight Percent (% ²³⁵U) Uranium in which the relative concentration of the fissile isotope Uranium-235 has been increased above its natural abundance (~0.72%). % U-235 Concentration (Low Enriched: 3–5%, High Enriched: >20%)

Feynman Diagram Nuclear & Particle Physics Calculational Diagram Visual pictorial representations of mathematical expressions describing the quantum interaction and scattering behavior of subatomic particles. Pictorial matrix elements M_fi in QFT perturbational expansions

Gamma Decay Nuclear & Particle Physics MeV or keV (Photon Energy) A radioactive decay process where an excited atomic nucleus transitions to a lower energy state by emitting a high-energy gamma-ray photon. ᴬ_Z X* → ᴬ_Z X + γ (High-energy photon emission)

Geiger-Müller Counter Nuclear & Particle Physics Counts per Minute (CPM) or μSv/h A gas-filled radiation detection instrument that measures ionizing radiation by detecting current pulses produced by Townsend avalanches in a high-voltage tube. Townsend Avalanche ionization in high electric fields

Gluons Nuclear & Particle Physics Gauge Boson Class Massless elementary gauge bosons that mediate the strong nuclear force between quarks in quantum chromodynamics (QCD). Spin = 1, Mass = 0, 8 Color-Anticolor Combinations

Hadrons Nuclear & Particle Physics Composite Particle Class Subatomic composite particles made of quarks and gluons held together by the strong nuclear force. Strongly interacting composite particles (Baryons & Mesons)

Half-Life Nuclear & Particle Physics Seconds, Hours, or Years The time required for half the radioactive nuclei in a given sample to undergo spontaneous radioactive decay. t_½ = ln(2) / λ ≈ 0.693 / λ, N(t) = N₀ (½)^(t / t_½)

Higgs Boson Nuclear & Particle Physics GeV/c² (Mass Energy) An elementary scalar boson associated with the Higgs field that endows fundamental particles with rest mass via electroweak symmetry breaking. m_H ≈ 125.1 GeV/c², Spin = 0, Scalar Field φ

Isobars Nuclear & Particle Physics Dimensionless Species Nuclides of different chemical elements that share the exact same mass number A (total number of nucleons) while having different atomic numbers Z. A = Z + N = Constant