Isidor Isaac Rabi

From the Nobel Foundation:

His early work was concerned with the magnetic properties of crystals. In 1930 he began studying the magnetic properties of atomic nuclei, developing Stern's molecular beam method to great precision, as a tool for measuring these properties. His apparatus was based on the production of ordinary electromagnetic oscillations of the same frequency as that of the Larmor precession of atomic systems in a magnetic field. By an ingenious application of the resonance principle he succeeded in detecting and measuring single states of rotation of atoms and molecules, and in determining the mechanical and magnetic moments of the nuclei.

"Isidor Isaac Rabi: Biographical," Nobel Foundation (1944)

Nobel Laureate, Physics Prize, 1944