Paper 2.11: "Absolute Value of the Proton g Factor," T. Myint, D. Kleppner, N. F. Ramsey and H. G. Robinson, Phys. Rev. Lett. 17, 405–407 (1966)
Reprinted with permission from Physical Review Letters. Copyright 1966, The American Physical Society.
Although the proton magnetic moment is fundamental in nuclear and atomic physics, all its measurements prior to this paper were in molecules where externally applied magnetic fields induced circulations of the electrons that magnetically shielded the proton. I had developed a theory of the shielding correction (Paper 5.1), but it was of limited accuracy and had never been tested. We therefore made a direct measurement of the absolute value of the proton magnetic moment, both to have a better value for this fundamental constant and to test my magnetic shielding theory. We successfully did this (Paper 2.11) by operating the hydrogen maser at a high magnetic field and observing both the proton and the electron spin flip frequencies. In the hydrogen atom, the relativistic correction for the electron spin flip and the magnetic shielding of the nucleus are known, so the proton moment is measured directly in terms of the electron moment. From the previously measured value of the electron moment, the value of the proton magnetic moment in Bohr magnetons is obtained. From this absolute value of the magnetic moment and the NMR measurements of the proton resonance frequency in H2, the magnetic shielding theory of Paper 5.1 was experimentally confirmed to within the estimated error.
