A particle much smaller than the @W06659@ of the radiation in the medium. In practice, all dimensions of a particle considered small must be less than about one-twentieth of the @W06659@ employed.
Source: Purple Book, 1st ed., p. 65 [Terms] [Book]
Citation: 'small particle' in IUPAC Compendium of Chemical Terminology, 3rd ed. International Union of Pure and Applied Chemistry; 2006. Online version 3.0.1, 2019. https://doi.org/10.1351/goldbook.S05713 RISBibTexEndNote