On the Passage of Neutrons Through Ferromagnets

The paper contains a treatment of various phenomena occurring in the passage of neutrons through domains which are regularly or irregularly magnetized. After setting up general equations for the behavior of the neutron spin in different types of magnetic fields which correspond approximately to various stages of magnetization in ferromagnets we obtain very general results for the depolarization of an originally polarized beam. These results can be easily extended to arbitrarily constituted beams. We report next, briefly, on current views concerning the domain structure of ferromagnets and discuss in detail the possibilities of investigating this structure by means of experiments with partially polarized neutron beams. The discussion divides itself naturally into the treatment of single crystals, macroscopically unmagnetized polycrystals and of polycrystals near magnetic saturation. Revising previous unsatisfactory treatments we derive in a very general manner formulae for the change of intensity and polarization of a neutron beam traversing a saturated or quasisaturated ferromagnetic medium. The formulae obtained constitute the basis for a modified theory of the well-known neutron polarization experiments. A closing paragraph contains a brief comparison between theory and experiment as far as it can be carried out without evaluating certain phenomenological constants, a task reserved for the following paper.