In 2012 it was asked, How to measure the spin of a neutral particle. I'm not sure that the answer "Neutron spin can be measured in a Stern Gerlach setup." was really carried out. So what for techniques are required to measure the spin of a neutron?


1 Answer 1


The spin of the neutron was measured by the Stern-Gerlach experiment by Sherwood, Stephenson and Bernstein (1954) (sadly paywalled, free links welcome),

Abstract: A neutron beam was polarized by total reflection from a magnetized iron mirror. The beam was then analyzed by passing it through an inhomogeneous magnetic field. From the deflection pattern obtained, it is inferred that the resultant neutron spin in the polarized beam was parallel to the magnetic field applied to the mirror. Thus the nuclear and magnetic scattering amplitudes for iron are of the same sign when the neutron spin and electronic spin are oppositely directed, and conversely.

So the techniques would be the same for any other Stern-Gerlach apparatus. Note that neutral particles will still have an intrinsic magnetic moment, so the Stern-Gerlach experiment would result in the split pattern.

  • $\begingroup$ Interesting. I know they are fermions but I am a bit surprised to learn that they interact with magnetic fields. I never really thought about it. How would this interaction be characterized by the standard model? $\endgroup$
    – Alex
    Aug 1, 2015 at 21:12
  • $\begingroup$ The spin was only parallel and not anti parallel too to the magnetic field? So the deflection from the magnetic field was in one direction only? $\endgroup$ Aug 1, 2015 at 21:17
  • $\begingroup$ What do you mean How would this interaction be characterized by the standard model? AFAIK, QM & SM are not at odds with each other, so asking if they're in conflict seems very strange. $\endgroup$
    – Kyle Kanos
    Aug 1, 2015 at 21:36
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    $\begingroup$ And the spin appears to be aligned parallel/anti-parallel to the magnetic field so the deflection would be either up or down (relating to the spin of the particle); that's kinda how the SG experiment works. $\endgroup$
    – Kyle Kanos
    Aug 1, 2015 at 21:37
  • $\begingroup$ This link describes a Stern-Gerlach experiment applied to potassium, but it seems to be an accessible and easy-to-understand account of the procedure and its significance: people.roma2.infn.it/~carboni/SternGerlach.pdf $\endgroup$
    – Ernie
    Aug 1, 2015 at 23:48

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