Description of neutron beams in magnetic media

The quantum aspects of the description of neutron beams in magnetic media a re discussed. 'Neutron polarization' and 'neutron beam polarization' are no t equivalent, as the former is related to the probability densities of neut ron spin states whereas the latter is related to the respective current den sities (intensities). The very presence of a magnetic field induces polariz ation of beam neutrons. As a consequence, neutron beams are polarized even by unpolarized nuclei. A possibility to produce the source of polarized ult racold neutrons is pointed out. (C) 1999 Elsevier Science B.V. All rights r eserved.