Contributions of magnetic resonance to other sciences

by Norman Ramsey

Wednesday 11 Oct 2006, 16:30 → 18:00 Europe/Zurich

500/1-001 - Main Auditorium (CERN)

One of the attractive features of fundamental research is the frequency with which new methods or discoveries in one narrow field of research eventually often make very important contributions to other fields. This has been conspicuously true of magnetic resonance, with which I have been associated ever since I.I. Rabi invented and demonstrated the method for the important but limited purpose of measuring nuclear magnetic moments. The following year we were surprised by the unexpected appearance of the H2 magnetic resonance, which we soon showed was due to the magnetic effects of the other proton and the rotating charged molecule; from these measurements we could also obtain important chemical and molecular information. We had another shock when we studied D2 and found the resonance curves were spread more widely for D2 than H2 even though the magnetic interactions should have been much smaller. We found we could explain this by assuming that the deuteron had an electric quadrupole moment and J. Schwinger pointed out that this would require the existence of a previously unsuspected electric tensor force between the neutron and the proton. With this, the resonance method was also giving new fundamental information about nuclear forces. In 1944, Rabi and I pointed out that it should be possible by the Dirac theory and our past resonance experiments to calculate exactly the hyperfine interaction between the electron and the proton in the hydrogen atom and we had two graduate students, Nafe and Nelson do the experiment and they found a disagreement which led J. Schwinger to develop the first successful relativistic quantum field theory and QED. In 1964, Purcell, Bloch and others detected magnetic resonance transitions by the effect of the transition on the oscillator, called NMR, making possible measurements on liquids, solids and gases and giving information on chemical shifts and thermal relaxation times T1 and T2. I developed a magnetic resonance method for setting a limit to the EDM of a neutron in a beam and with others for neutrons stored in a suitably coated bottle. Magnetic resonance measurements provide high stability atomic clocks. Both the second and the meter are now defined in terms of atomic clocks. Lauterbuhr, Mansfield and Damadian and others developed the important methods of using inhomogeneous magnetic fields to localize the magnetic resonance in a tissue sample producing beautiful and valuable magnetic resonance images, MRI’s, and fMRI’s.