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Spinning water can change the alignment of its hydrogen nuclei—the protons in its molecules—enough to alter a nuclear magnetic resonance (NMR) signal. In a 2019 laboratory experiment, researchers detected this rotation-associated proton polarization in water rotating at up to 13.5 kHz. The result demonstrated the nuclear Barnett effect; it did not create a practical MRI method or show that ordinary water becomes visibly or permanently magnetized.
What is the nuclear Barnett effect?
The Barnett effect is magnetization associated with rotation. Its established electronic form concerns the spins of electrons. In 2019, Mohsen Arabgol and Tycho Sleator of New York University reported observing the nuclear counterpart: rotation-associated polarization of the protons in water. Their paper, “Observation of the Nuclear Barnett Effect,” appeared in Physical Review Letters on May 2, 2019. Read the paper abstract.
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Proton polarization describes a change in how nuclear spins are aligned or populated. It is not a claim that water became a permanently magnetized object. The researchers detected the change indirectly by measuring the size of the sample’s NMR signal.
How did spinning water change the NMR measurement?
The rotating sample
The researchers rotated a water sample in a weak magnetic field, reaching a maximum rotation rate of 13.5 kHz, or 13,500 revolutions per second. The American Physical Society’s explanation describes the water as occupying a hollow section of a rotating rod measuring 2 mm by 8 mm. These details describe the laboratory setup, not a consumer device. See the APS explanation.
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The signal as evidence
NMR detects nuclear spins through their response to a magnetic field. Arabgol and Sleator looked for a change in the NMR signal’s size as the sample rotated. The primary paper reports that the change in polarization was proportional to rotation frequency. The APS account describes the measured magnetization increase as about 1% over the small effect induced by the NMR technique at just over 4,000 revolutions per second, rising to just over 3% at 13,500 revolutions per second. Those percentages use the experiment’s small NMR-induced effect as their reference; they are not absolute polarization values, efficiency figures, or improvements in an imaging system.
Did rotation create a real magnetic field?
The researchers observed no NMR frequency shift attributable to rotation. Their paper states: “No NMR frequency shift was observed due to rotation, meaning that this magnetization was not produced by a real magnetic field.” In other words, the reported rotation-associated magnetization was inferred from the change in signal size, while the expected frequency-shift evidence for an additional real magnetic field was absent.
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Does this mean spinning water can power an MRI?
No practical MRI method follows from this result. The cited reports establish a measurement of proton polarization in a laboratory water sample under high-speed rotation and a weak magnetic field. They do not demonstrate a medical imaging system, a usable MRI technique, or an application outside the experiment. The result is a physics observation, not evidence that water spun in everyday conditions becomes a useful magnet.
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The experiment extended the idea of rotation-associated magnetization from electronic spins to nuclear spins: in this case, the hydrogen protons in water. Chemistry World’s contemporaneous report places the work in that context and identifies Arabgol and Sleator as the NYU researchers. Read the Chemistry World report. The available sources establish the original 2019 laboratory observation; they do not establish whether it has since been independently replicated or led to a practical application.
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