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Edward Mills Purcell Created 2026-10-18 Updated 2026-11-05
Edward Mills Purcell, Henry Cutler Torrey and Robert Vivian Pound observed nuclear magnetic resonance through absorption in a bulk solid. A static magnetic field separates nuclear magnetic energy levels, and an applied radiofrequency field drives resonant transitions. Measuring the absorbed signal connects a microscopic nuclear moment with a laboratory electromagnetic circuit. The experiment helped make nuclear-spin behavior accessible in ordinary condensed samples.[ref]
Resonance Absorption by Nuclear Magnetic Moments in a Solid by Edward Mills Purcell and others. Physical Review 69, 37 (1946), bulk resonance-absorption observation
Portrait of Edward Mills Purcell
. Unknown photographer; Nobel Foundation, Les Prix Nobel en 1952, editor Göran Liljestrand, Stockholm 1953. Commons PD-Sweden photograph claim, with a request for an additional US public-domain tag. Rights elsewhere are not independently determined., via Wikimedia Commons. Source.
Henry Cutler Torrey Created 2026-10-18 Updated 2026-11-05
An experimental physicist who coauthored observation of nuclear magnetic resonance in a solid with Edward Mills Purcell and Robert Vivian Pound. A radiofrequency field drives transitions of nuclear magnetic moments in an applied magnetic field; resonance appears as enhanced absorption. The method provided access to nuclear properties without requiring a freely traveling atomic beam.[ref]
Resonance Absorption by Nuclear Magnetic Moments in a Solid by Edward Mills Purcell and others. 1946 letter: bulk solid resonance absorption
Edward Mills Purcell, Henry Cutler Torrey, and Robert Vivian Pound placed paraffin wax in a capacitively loaded coaxial cavity near 30 MHz between magnet poles. Coupling loops supplied and extracted power; oscillating and steady fields were perpendicular. Output balanced against a generator reference fed amplification, detection and a microammeter. A slow field sweep revealed absorption above fluctuations at room temperature. Weak drive avoided population equalization. Calibration was rough; field inhomogeneity could contribute to linewidth.[ref]
Resonance Absorption by Nuclear Magnetic Moments in a Solid by Edward Mills Purcell and others. pp. 37–38, apparatus and results; weak drive, balanced cavity output, microammeter, field sweep, calibration and linewidth limitations
Two electrical routes to bulk nuclear magnetic resonance
. Original functional diagrams of the distinct instruments described above. Arrows show connections and field directions, not scale or winding geometry. Details.
These are driven experiments with continuous radiofrequency excitation and changing static field, not demonstrations of modern pulsed Fourier transform nuclear magnetic resonance. Bloch's theoretical paper explicitly distinguishes proposed free precession after a pulse from the forced precession actually studied.[ref]
Nuclear Induction by Felix Bloch. pp. 460–461, introduction: proposed pulse/free-precession experiment versus performed forced-precession experiment
An experimental failure need not mean absent nuclear magnetic moments. In the model below, excessive drive reduces the population imbalance through nuclear magnetic resonance saturation; waiting too briefly can leave insufficient polarization. Separately, ordinary electrical losses can cause heating without identifying a nuclear resonance. The absorption experiment measured a balanced electrical signal, rather than using heating as its readout. Useful diagnostic checks include moving off resonance, changing the frequency, checking field uniformity and reducing drive. These are general checks; the historical operations actually documented are specified above.