https://doi.org/10.1351/goldbook.I03196
The ratio of the number of ions formed to the number of electrons or photons used in an @I03183@ process.
Source:
PAC, 1991, 63, 1541. (Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)) on page 1548 [Terms] [Paper]