Ion moving with a velocity exceeding the Bohr speed of
\(c/137\), where
\(c\) is the velocity of light.
Note: For argon and gold, this criterion requires energies greater than \(\pu{1 MeV}\) and \(\pu{5 MeV}\), respectively.
Source:
PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1836 (https://doi.org/10.1515/pac-2019-0404)