AQA A-Level Physics - Nuclear Physics Definitions

AQA A-Level Physics - Nuclear Physics Definitions

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

Nucleon

A particle in the nucleus: either a proton or a neutron.

Atomic Number (Z)

The number of protons in an atom's nucleus.

Mass Number (A)

The total number of protons and neutrons in an atom's nucleus.

Radioactive Decay

The spontaneous and random emission of radiation from an unstable nucleus.

Alpha Decay (α)

Emission of a helium nucleus (2 protons and 2 neutrons).

Beta Minus Decay (β⁻)

Neutron transforms into a proton, emitting an electron and an antineutrino.

Beta Plus Decay (β⁺)

Proton transforms into a neutron, emitting a positron and a neutrino.

Gamma Decay (γ)

Emission of a high-energy photon with no change in mass or atomic number.

Electron Capture

A proton in the nucleus captures an inner-shell electron and becomes a neutron.

Activity (A)

The number of nuclear decays per second, measured in becquerels (Bq).

Decay Constant (λ)

The probability per unit time that a nucleus will decay.

Half-Life (t₁/₂)

Time taken for half the radioactive nuclei in a sample to decay.

Random, Spontaneous Process

The unpredictable nature of individual nuclear decays, but statistically reliable over large numbers.

Mass Defect

The difference between the total mass of the separated nucleons and the mass of the nucleus.

Binding Energy

The energy required to break a nucleus into its component nucleons.

Binding Energy per Nucleon

The binding energy divided by the number of nucleons; indicates nuclear stability.

Nuclear Force

The strong, short-range attractive force that holds nucleons together.

Nuclear Instability

Occurs when a nucleus has an imbalance of neutrons and protons or is too massive.

Nuclear Fission

Splitting of a heavy nucleus into lighter nuclei, releasing energy and neutrons.

Nuclear Fusion

Joining of light nuclei to form a heavier nucleus, releasing energy.

Chain Reaction

A self-sustaining reaction where the products cause further reactions.

Critical Mass

The minimum amount of fissile material needed to maintain a chain reaction.

Q-Value

The net energy change in a nuclear reaction, calculated from mass difference.

Nuclear Radius

Proportional to A^(1/3); typical values are in femtometres (1 fm = 1 x 10^-15 m).

Nuclear Density

Approximately constant across all nuclei; much greater than atomic density.