GLOBAL KNOWLEDGE ARK

Reference library

Foundations

Explore concepts, laws, equations and methods, with clear explanations of their use and sources. Choose an area of study or find a specific entry.

More filters

Reference entries

Showing 241–270 of 1709 reference entries

Physics · Earth & cosmosNuclear binding energy

A bound nucleus has less rest mass than its separated nucleons.

ModelPhysics · Earth & cosmosExponential radioactive decay

A fixed decay probability per time gives a population timescale.

ModelPhysics · Earth & cosmosFission, fusion and reaction energy

Nuclear rearrangement can release or require energy.

ModelPhysicsScattering cross section

Normalize a scattering rate by incident flux.

ModelPhysicsStandard Model matter families

Quarks and leptons form three generations.

ModelPhysicsStandard Model interactions

Gauge fields mediate three interactions; the Higgs is a scalar sector.

ModelPhysicsInteraction-specific quantum-number balances

A balance rule must name the interaction where it applies.

ModelPhysics · ChemistryBloch states and electronic bands

A periodic crystal potential organizes energies by wavevector and band.

ModelPhysics · ChemistrySemiconductor electrons and holes

Band occupancy and doping control mobile carriers.

ModelPhysicsBose and Fermi thermal occupations

Indistinguishable particles have different equilibrium state populations.

ModelChemistryElectron screening and effective nuclear attraction

Other electrons modify the attraction experienced by an electron in an atom.

ModelChemistryMultielectron ground-state configurations

Orbital occupations connect atomic electronic structure with valence chemistry.

ModelChemistryLocalized bonds and resonance descriptions

Localized orbital overlap and resonance are complementary chemical descriptions.

ModelChemistryMolecular orbitals and bonding occupation

A molecular orbital description distributes electronic states across a molecule.

ModelChemistryIntermolecular interactions

Dispersion, dipole interactions and hydrogen bonding influence molecular materials.

ModelChemistryBonding classes of solids

Ionic, metallic, molecular and network solids organize common bonding patterns.

DefinitionChemistryPolymers and macromolecular architecture

Polymers are substances composed of macromolecules with recurring structural units.

DefinitionChemistryCoordination compounds and ligands

Ligand donor atoms surround a central metal in a coordination sphere.

DefinitionChemistryActivities and chemical potentials

Activity expresses composition relative to a specified thermodynamic standard state.

DefinitionChemistrypH and hydrogen-ion activity

pH is an activity-based quantity realized through measurement conventions.

DefinitionChemistryBuffers and finite buffering capacity

An acid–base pair can resist limited changes in solution pH.

ModelChemistrySolubility products and precipitation

An equilibrium product constrains dissolution of a specified solid phase.

ModelChemistryReference electrodes and redox potentials

Electrode potentials are specified relative to a reference half-cell.

DefinitionChemistryThe Nernst equilibrium relation

Reversible electrochemical potential depends on activities and temperature.

ModelChemistryElementary steps and reaction mechanisms

A mechanism proposes steps that account for an overall chemical transformation.

ModelChemistryArrhenius temperature dependence

Many rate constants follow an exponential temperature model over a limited range.

ApproximationChemistryHess's law and thermochemical accounting

Reaction enthalpies can be combined because enthalpy is a state function.

ModelChemistryPhase diagrams and coexistence

Phase diagrams describe equilibrium states under stated conditions.

ModelChemistryCalibration, standards and matrix effects

Quantitative analysis needs a validated relation between response and analyte amount.

MethodChemistryChromatographic retention and separation

Differential interactions with mobile and stationary phases separate mixture components.

Method
ModelSource checked

Fission, fusion and reaction energy

PhysicsEarth & cosmos

Nuclear rearrangement can release or require energy.

Key knowledge

Fission splits a nucleus into smaller products; fusion combines nuclei. Reaction Q = (Σm_initial − Σm_final)c² measures rest-energy release: Q > 0 is exothermic and Q < 0 requires energy input.

Values and equations

Q = (Σm_initial − Σm_final)c²

Q
Reaction rest-energy release J
m_initial, m_final
Participant rest masses under a consistent convention kg
c
Vacuum light speed m s⁻¹

Conditions and scope

  • Include all reaction participants and use consistent nuclear or atomic mass accounting.
  • Neither all fission nor all fusion reactions are exothermic; positive Q alone does not establish reaction rate or overcome barriers.
Sources · 2

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. Samuel J. Ling, Jeff Sanny and William Moebs / OpenStax, Rice University2 sources
    1. University Physics 3: FissionSamuel J. Ling, Jeff Sanny and William Moebs / OpenStax, Rice UniversityTextbook chapteropenstax.orgRead source
    2. University Physics 3: Nuclear FusionSamuel J. Ling, Jeff Sanny and William Moebs / OpenStax, Rice UniversityTextbook chapteropenstax.orgRead source

Evidence and review

Nuclear splitting/combining definitions and rest-mass/binding-energy release examples.

2026-10-10 · Reaction definitions and Q balance only; reactor design, rates and numerical yields excluded.

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–6 of 6 relationships

Scientific relationships · 6 / 6

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Uses definition
    Relationship sources · 2

    Linked statements

    • Fission splits a nucleus into smaller products; fusion combines nuclei. Reaction Q = (Σm_initial − Σm_final)c² measures rest-energy release: Q > 0 is exothermic and Q < 0 requires energy input.

    Changes in binding/rest energies determine the reaction Q under consistent mass accounting.

  2. Related to
    Relationship sources · 1

    Linked statements

    • Main-sequence stars sustain core hydrogen fusion. As core hydrogen is depleted, core and envelope structure change and subsequent evolution depends strongly on mass. Sun-like stars can develop giant phases and helium fusion, while sufficiently massive stars undergo further nuclear-burning stages.

    Stellar fuel stages involve fusion; this relation makes no claim that fission powers main-sequence stars.

  3. Uses definition
    Relationship sources · 2

    Linked statements

    • An alpha channel changes (A,Z) to (A−4,Z−2) plus ⁴He. A positive Q supplies relative kinetic energy but does not bypass the daughter–alpha Coulomb barrier. In an s-wave exterior model V(r)=κ/r, the opaque-barrier factor is T≈exp[−2∫_R^(κ/Q)√(2μ(κ/r−Q))dr/ħ]; an effective channel attempt frequency f gives λ_α≈fT, so the rate depends exponentially on the barrier as well as on nuclear structure.

    Consistent bare-nucleus channel mass accounting determines Q and relative exterior kinetic energy; it does not determine the rate.

  4. Uses definition
    Relationship sources · 1

    Linked statements

    • For projectile rest mass m_a and target m_A initially at rest, squared center-of-momentum energy is E_cm²=(m_a+m_A)²c⁴+2m_Ac²K_a. If the minimum allowed final invariant mass is M_f, an endothermic channel requires K_thr=[M_f²−(m_a+m_A)²]c²/(2m_A). With Q=(m_a+m_A−M_f)c² this becomes −Q(1+m_a/m_A)+Q²/(2m_Ac²), showing why laboratory threshold generally exceeds −Q.

    The channel Q uses the same complete rest-mass difference; target recoil distinguishes laboratory threshold from −Q.

  5. Related to
    Relationship sources · 2

    Linked statements

    • Fission can emit neutrons that induce further fissions, while capture without fission and leakage remove neutrons from the chain. In a fixed linear generation model the effective multiplication factor k is the ratio of successive expected neutron generations: N_g=N₀k^g. A chain is subcritical for k<1, critical for k=1 and supercritical for k>1. Criticality balances production and losses; it is not a universal material-mass threshold independent of geometry and environment.

    Neutron-emitting fission can feed a next generation; consistent reaction energy does not alone establish net multiplication.

  6. Related to
    Relationship sources · 2

    Linked statements

    • In a dilute nondegenerate gas of independently distributed reacting nuclei at common temperature T, reaction events per volume/time are R_ab=n_an_b⟨σv⟩/(1+δ_ab), where δ_ab=1 for the same species and 0 otherwise. The nonrelativistic Maxwell relative distribution gives ⟨σv⟩=√[8/(πμ)](k_BT)⁻³ᐟ²∫₀∞σ(E)Eexp[−E/(k_BT)]dE, using relative energy E=μv²/2. The identical-species factor counts each incoming pair once.

    A channel's Q controls rest-energy accounting while its rate requires actual cross sections and a specified reactant distribution.

Entry detailsPermanent link to this entry ↗
Record identity
physics-fission-fusion
Revision
university-reference.1
Structured reference record
University reference · University core expansion