Noun
hyperfine structure (plural hyperfine structures)
(physics) a closely spaced structure of lines in the spectrum of an atom or molecule due to nuclear isotopic effects and/or to nuclear spin
In June 2011, trapped 309 antihydrogen atoms, up to 3 simultaneously, for up to 1,000 seconds. citation citation They then studied its hyperfine structure, gravity effects, and charge. Source: Internet
Before Essen's invention, the second was defined on the orbit of the Earth around the Sun ; he changed it in 1967 to be based on the hyperfine structure of the caesium-133 atom. Source: Internet