Listen to Protons With a Homemade Magnetometer

When you get an MRI scan, the machine exploits a phenomenon called nuclear magnetic resonance (NMR). Certain kinds of atomic nuclei—including those of the hydrogen atoms in a water molecule—can be made to oscillate in a magnetic field, and these oscillations can be detected with coils of wire. MRI scanners employ intense magnetic fields that create resonances at tens to hundreds of megahertz. However, another NMR-based instrument involves much lower-frequency oscillations: a proton-precession…