particle flux density

symbol: j, units: m−2s−1, cm−2s−1
synonyms: fluence rate (obsolete), photon flux density
https://doi.org/10.1351/goldbook.08747
Number of particles (or photons) incident on a plane perpendicular to the incident radiation per unit time per unit area.
Notes:
  1. Particle flux density is identical with the product of the particle density and the average speed of the particles.
  2. The SI unit of flux density is m−2s−1.
  3. Often an indication of the type of incident particles is wrongly added to the unit of flux density, e.g., the neutron flux density is sometimes indicated as n cm−2s−1. As 'n' is not a unit, it is metrologically unacceptable and therefore not recommended.
Source:
PAC, 2021, 93, 69. (Vocabulary of radioanalytical methods (IUPAC Recommendations 2020)) on page 91 [Terms] [Paper]
Citation: 'particle flux density' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.08747 RIS BibTex EndNote
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