Nuclear & Radiochemistry — 60 Terms Defined

Alpha Decay Nuclear & Radiochemistry MeV Radioactive decay in which a nucleus emits a helium-4 nucleus, losing two protons and two neutrons. ᴬ_Z X → ᴬ⁻⁴_Z₋₂ Y + ⁴₂He

Artificial Radioactivity Nuclear & Radiochemistry Bq Radioactivity in nuclides created by bombarding stable nuclei with particles rather than found in nature.

Background Radiation Nuclear & Radiochemistry mSv/year The ionising radiation always present in the environment from natural and artificial sources.

Band of Stability Nuclear & Radiochemistry Dimensionless The region on a plot of neutron number against proton number within which stable nuclides are found.

Becquerel Nuclear & Radiochemistry Bq The SI unit of radioactivity, equal to one nuclear disintegration per second. 1 Bq = 1 s⁻¹

Beta-Minus Decay Nuclear & Radiochemistry MeV Radioactive decay in which a neutron converts into a proton, emitting an electron and an antineutrino. n → p + e⁻ + ν̄

Binding Energy per Nucleon Nuclear & Radiochemistry MeV/nucleon The nuclear binding energy divided by the number of nucleons, measuring the stability of a nucleus. BE/A

Breeder Reactor Nuclear & Radiochemistry Dimensionless A reactor that produces more fissile material than it consumes by converting fertile nuclides. ²³⁸U + n → ²³⁹Pu

Cloud Chamber Nuclear & Radiochemistry Dimensionless A device that reveals the paths of ionising particles as visible trails of condensed vapour.

Control Rod Nuclear & Radiochemistry Dimensionless A movable rod of neutron-absorbing material used to regulate the rate of a nuclear chain reaction.

Critical Mass Nuclear & Radiochemistry kg The minimum mass of fissile material needed to sustain a nuclear chain reaction.

Curie Nuclear & Radiochemistry Ci The older unit of radioactivity, defined as the activity of one gram of radium-226. 1 Ci = 3.7 × 10¹⁰ Bq

Decay Constant Nuclear & Radiochemistry s⁻¹ The probability per unit time that a given nucleus will decay. λ = 0.693 / t½

Electron Capture Nuclear & Radiochemistry MeV Radioactive decay in which a nucleus absorbs an inner-shell electron, converting a proton into a neutron. p + e⁻ → n + ν

Gamma Emission Nuclear & Radiochemistry MeV The release of high-energy electromagnetic radiation from a nucleus dropping to a lower energy state. ᴬ_Z X* → ᴬ_Z X + γ

Geiger–Müller Counter Nuclear & Radiochemistry counts/s An instrument that detects ionising radiation through the avalanche of ionisation it triggers in a low-pressure gas.

Gray Nuclear & Radiochemistry Gy The SI unit of absorbed radiation dose, equal to one joule of energy deposited per kilogram of matter. 1 Gy = 1 J/kg

Ionising Radiation Nuclear & Radiochemistry eV Radiation with enough energy to remove electrons from atoms, creating ions.

Isotope Dilution Analysis Nuclear & Radiochemistry mol A quantitative technique in which a known amount of labelled isotope is added and the resulting dilution measured. n_unknown = n_spike(R_spike/R_mix − 1)

Law of Radioactive Decay Nuclear & Radiochemistry Dimensionless The principle that the rate of decay is proportional to the number of undecayed nuclei present. N = N₀ e^(−λt)

Magic Numbers Nuclear & Radiochemistry Dimensionless Particular numbers of protons or neutrons that give a nucleus exceptional stability. 2, 8, 20, 28, 50, 82, 126

Mass Defect Nuclear & Radiochemistry u The difference between the mass of a nucleus and the sum of the masses of its constituent nucleons. Δm = Zm_p + Nm_n − m_nucleus

Moderator Nuclear & Radiochemistry Dimensionless A material used in a reactor to slow fast neutrons to energies at which fission is far more probable.

Neutron Emission Nuclear & Radiochemistry MeV The direct ejection of a neutron from an extremely neutron-rich nucleus. ᴬ_Z X → ᴬ⁻¹_Z X + ¹₀n