\(\mathit{\Phi} = \rm{d}N/\rm{d}t\), where
\(N\) is number of particles of a specified type and
\(t\) is time.
Notes: - For a parallel beam, fluence rate and flux density are equivalent measures.
- SI unit: \(\pu{s^{-1}}\). For a beam of charged particles (ions) the flux is expressed in ampere, i.e. \(F \times ze\), where \(z\) is the charge on a particle and \(e\) the elementary charge (\(\pu{1.602176634E-19 C}\)).
Source:
PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1804 (https://doi.org/10.1515/pac-2019-0404)