Definition of "hyperfine" [hyperfine]

• Extremely fine, especially of the hyperfine structure in the spectra of atoms and molecules. (adjective)

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• "The magnetic field separates these levels into two "hyperfine" states."
• "Have you a device by which I might measure the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom?"
• "They feature a picture of the solar system, a picture of the probes and a pictorial representation of the hyperfine transition of neutral hydrogen."