The number of ions produced as a function of the energy of the electrons or photons used to produce
ionization
.
Sources: Orange Book, 2nd ed., p. 206 [Terms] [Book] 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]