Reprinted in The Physical Review - the First Hundred Years, AIP Press (1995) CD-ROM.
The intrinsic angular momenta of the proton and the deuteron imply a neutron spin (in units of h) of either 1 / 2 or 3 / 2. The usual assumption of 1 / 2 for the neutron spin is based entirely upon arguments of simplicity, since either of these two possible values is consistent with data on nuclear spins. In view of the importance of the neutron spin in nuclear theory, it would be desirable to determine this quantity by direct experiment. It has recently been shown that experiments on the
scattering of neutrons by ortho- and parahydrogen would enable one to obtain information about the spin dependence and the range of the neutron-proton interaction. It is the purpose of this note to point out that such experiments also permit the determination of the neutron spin... The experiments of both Dunning and Stern and their collaborators show that the scattering cross section of ortho-H2 at liquid-air neutron temperatures (T= 100°K) is much larger than the
corresponding para-H2 cross section. It has already been pointed out that this result is in agreement with the theoretical expectations for a virtual singlet state. Assuming a neutron spin of 3 / 2 h the theoretical value of the ratio ortho/para, at an energy of 3kT/2 = 0.012 eV, is 3.11 for a virtual quintet state and 1.09 for a real quintet state. In either case, the two cross sections
are quite comparable in magnitude, in contradiction with experiment. On the basis of these experiments the conclusion must be drawn that the intrinsic angular momentum of the neutron is, in reality, 1 / 2 h. (Extracted from the introductory part of the paper.).
Related references See also J. Schwinger and E. Teller, Phys. Rev. 52 (1937) 286;
E. Fermi, La Ricerca Scientifica VII-II (1936) 13;
Analyse data from J. Halpern, I. Esterman, O. C. Simpson, and O. Stern, Phys. Rev. 52 (1937) 142;
Establishment of the neutron spin 1/2.