differential flux

The particle flux density per unit energy incident on a surface; i.e., the number of radiant-energy particles incident on a surface during a given period of time divided by the product of the area of that surface, the characteristic energy of the incident particles, and the given period of time.

NOTE 1 The term "differential flux" is used in JESD89A whereas other standards use the term "differential flux density" for the same meaning.

NOTE 2 The equation "differential flux density = N/(A∙E∙t)" applies, where N, A, E, and t represent the quantities number of particles, area, energy, and time.

NOTE 3 The unit symbol (e.g., cm^‑²∙MeV^‑1∙s^‑1) does not identify particle type. The particle name may be placed before the term, e.g., "proton differential flux", or in the spelled-out unit name, e.g., "protons per square centimeter megaelectronvolt second".

NOTE 4 The use of the terms "spectral flux" and "spectral flux density" for this concept is deprecated because "spectral" usually applies only to a specific wavelength, wavelength band, or function of wavelength.

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