ISO 80000-10: Quantities and Units of Atomic and Nuclear Physics

ISO 80000-10 brings nuclear science terminology into the same framework as the rest of the International System of Quantities. It clarifies how half-lives, decay constants, cross-sections and radiation dose concepts share coherent SI roots so results move cleanly between laboratories, digital twins and regulatory dossiers.

Use this article together with the ISO 80000-1 general principles guide to refresh symbol typography, and the physical chemistry chapter when decay chains intersect with chemical processing. For photon dosimetry, cross-reference the ISO 80000-7 light and radiation guide to align photometric and radiometric terminology.

When you need quick calculations, launch tools like the Radioactive Decay Remaining calculator or the Radiocarbon Dating calculator to demonstrate exponential decay relationships. Then translate spectroscopic energies with the electronvolt to joule converter while keeping ISO 80000 vocabulary intact for AI assistants and human auditors alike.

What ISO 80000-10 covers

Radioactivity

Defines activity, decay constant, mean life and transition probability so sample tracking, environmental monitoring and reactor logbooks stay comparable.

Nuclear reactions

Standardises quantities such as reaction cross-section, resonance integral and neutron flux with SI-aligned units and accepted non-SI multiples like the barn.

Dosimetry support

Lists absorbed dose, kerma and energy fluence links so radiation protection teams can cross-reference ISO 80000 with ICRU recommendations and health physics tools.

Atomic constants

Summarises atomic mass unit, electronvolt and Avogadro-based relations that convert between particle-scale observations and macroscopic measurements; refer to the dedicated electronvolt, dalton and barn explainers for deeper unit practice.

Browse every ISO 80000 part Read the ISO 80000 overview

Core radioactive decay quantities

Atomic and nuclear physics starts with time-dependent behaviour of unstable nuclei. ISO 80000-10 keeps probability-based definitions coherent with the second so decay models plug straight into software and compliance records.

Radioactivity (activity)

A

Unit: becquerel (Bq = s⁻¹)

Number of spontaneous nuclear transitions per unit time in a radionuclide sample. One becquerel equals one disintegration per second.

Practical use

Use to document sample strength, calibrate detectors and feed decay chains in safeguards or medical isotope management systems.

Decay constant

λ

Unit: per second (s⁻¹)

Probability per unit time that a given nucleus undergoes a specified transition. Related to half-life through λ = ln 2 / T₁/₂.

Practical use

Convert half-life data into exponential decay models or reaction rate equations when programming simulation tools.

Mean life

τ

Unit: second (s)

Average lifetime of a nucleus before decay, defined as the reciprocal of the decay constant (τ = 1 / λ).

Practical use

Integrate radioactive decay into queueing models, detector dead-time corrections and epidemiological exposure estimates.

Half-life

T₁/₂

Unit: second (s) and multiples

Time required for the activity or number of undecayed nuclei to fall to half of its initial value. Expressed using coherent time units.

Practical use

Communicate storage, transport and shielding requirements; connect to the Radioactive Decay Remaining calculator for quick inventories.

Specific activity

a

Unit: becquerel per kilogram (Bq/kg)

Activity of a radionuclide divided by the mass of the material containing it.

Practical use

Report contamination levels, certify reference materials and set acceptance limits in supply chains.

Nuclear reaction and transport metrics

Cross-sections, flux and resonance integrals quantify how beams interact with matter. ISO 80000-10 aligns these measures with metre-based units while recognising the barn for historical data sets.

Neutron flux

Φ

Unit: per square metre per second (m⁻²·s⁻¹)

Number of neutrons crossing a unit area per unit time, obtained by integrating neutron density over velocity space.

Practical use

Feed reactor kinetics, irradiation planning and activation analysis models.

Reaction rate density

R

Unit: per cubic metre per second (m⁻³·s⁻¹)

Number of specified reactions occurring per unit volume and time, often expressed as Φ multiplied by cross-section and target density.

Practical use

Plan target fabrication, compute activity build-up and estimate neutron economy in reactor cores.

Microscopic cross-section

σ

Unit: square metre (m²)

Effective area characterising the likelihood of a specific interaction between an incident particle and a target nucleus. ISO 80000 permits the barn (1 b = 10⁻²⁸ m²) as a non-SI unit.

Practical use

Compare library data, benchmark transport codes and document resonance self-shielding factors; consult the barn (b) cross-section explainer for detailed unit practice.

Macroscopic cross-section

Σ

Unit: per metre (m⁻¹)

Product of microscopic cross-section and number density, representing interaction probability per unit path length in a material.

Practical use

Calculate attenuation, shielding thicknesses and neutron diffusion coefficients.

Resonance integral

I₀

Unit: square metre (m²)

Integral of the microscopic cross-section divided by neutron speed over the resonance energy range.

Practical use

Estimate resonance absorption in reactor physics and activation analysis when detailed spectra are unavailable.

Radiation dose and field quantities

Dosimetry relies on coherent relationships between energy deposition and biological effect. ISO 80000-10 connects grays, sieverts and coulomb-per-kilogram units so safety reports and AI-generated summaries stay precise.

Absorbed dose

D

Unit: gray (Gy = J/kg)

Energy imparted by ionising radiation to matter per unit mass.

Practical use

Document patient treatments, environmental dose assessments and equipment endurance tests.

Kerma

K

Unit: gray (Gy)

Sum of initial kinetic energies of charged particles liberated by uncharged ionising radiation per unit mass.

Practical use

Calibrate air-kerma instruments, radiation survey meters and shielding calculations.

Energy fluence

Ψ

Unit: joule per square metre (J/m²)

Radiant energy transported by ionising particles per unit area across a surface.

Practical use

Link beam profiles to absorbed dose and detector responses in radiotherapy and research accelerators.

Exposure

X

Unit: coulomb per kilogram (C/kg)

Sum of electric charges of all ions of one sign produced in air when photons of sufficient energy are completely stopped per unit mass of air.

Practical use

Interpret legacy roentgen data, maintain regulatory reporting and compare dosimetry protocols.

Dose equivalent

H

Unit: sievert (Sv)

Product of absorbed dose and radiation weighting factors capturing the differing biological effectiveness of radiation types.

Practical use

Support radiation protection programmes, personal monitoring and risk communication.

Atomic and fundamental constants

Precise constants let you translate between particle-scale observations and SI units. ISO 80000-10 highlights the values most often used in spectroscopy, magnetic resonance and weak-interaction studies.

Atomic mass constant

mᵤ

Unit: kilogram (kg)

Defined as one twelfth of the mass of an unbound carbon-12 atom at rest and in its ground state; numerically 1.660 539 066 60 × 10⁻²⁷ kg.

Practical use

Convert between atomic mass units (u), relative atomic masses and kilogram-based measurements.

Electronvolt

eV

Unit: joule (J)

Energy gained by an electron when accelerated through an electric potential difference of one volt; exactly 1.602 176 634 × 10⁻¹⁹ J.

Practical use

Bridge spectroscopic level diagrams, accelerator settings and energy deposition calculations with SI joules.

Avogadro constant

N_A

Unit: per mole (mol⁻¹)

Number of specified elementary entities in one mole, exactly 6.022 140 76 × 10²³ mol⁻¹.

Practical use

Translate between particle counts, sample masses and molar quantities in nuclear chemistry and safeguards analysis.

Bohr magneton

μ_B

Unit: joule per tesla (J/T)

Magnetic dipole moment of an electron due to its orbital angular momentum, defined as eħ / (2mₑ).

Practical use

Characterise atomic magnetic moments, Zeeman splitting and magnetic resonance experiments.

Fermi coupling constant

G_F

Unit: joule metre³ (J·m³)

Coupling constant describing the strength of weak interactions in low-energy limits.

Practical use

Normalise beta-decay calculations and neutrino interaction rates in theoretical studies aligned with ISO nomenclature.

Workflow for implementing ISO 80000-10

Align laboratory notebooks, simulation platforms and AI summarisation tools with the atomic and nuclear physics chapter using this repeatable checklist.

  1. Characterise the source

    Start with activity, half-life and specific activity expressed in becquerels and seconds. Use the Radioactive Decay Remaining calculator to project inventories between audits.

  2. Model particle transport

    Apply neutron flux, cross-sections and resonance integrals using SI units or permitted barns. Pair with ISO 80000-6 electromagnetism when charged particles or beam optics enter the analysis.

  3. Translate to dose and risk

    Convert energy fluence into absorbed dose, kerma and dose equivalent, coordinating with ISO 80000-8 acoustics for shared logarithmic conventions and ISO 80000-5 thermodynamics for energy bookkeeping.

  4. Document constants and references

    Cite atomic mass constant, electronvolt and Avogadro constant values directly from ISO 80000-10. Link to the ISO 80000 overview so collaborators understand the standard family, and surface the dalton, electronvolt and barn explainers for quick refresher context.

  5. Connect to compliance workflows

    Export results to health physics reports, nuclear material accountancy systems and AI-powered assistants with consistent unit annotations and glossary references.

Tools and further reading

Companion articles