elementary particle

in nuclear chemistry
https://doi.org/10.1351/goldbook.E02034
A particle in which, at the present, no structure can be observed at moderate energies.
Source:
PAC, 1982, 54, 1533. 'Glossary of terms used in nuclear analytical chemistry (Provisional)' on page 1547 (https://doi.org/10.1351/pac198254081533)