Neutron Polarization and Ferromagnetic Saturation

Abstract

The transmission of thermal neutrons through magnetized iron has been measured in its dependence upon the percentage deviation $\ensuremath{\epsilon}$ from saturation and upon the thickness $d$ of the sample. In agreement with the theory of Halpern and Holstein it was found that the percentage increase of transmission caused by magnetization is given by $(\frac{{n}^{2}{p}^{2}{d}^{2}}{2})f(\frac{\ensuremath{\lambda}}{\ensuremath{\epsilon}d})$, where $n$ is the number of iron atoms per unit volume. Writing for the scattering cross section of neutrons with parallel or antiparallel orientation of their spin with respect to the field, respectively ${\ensuremath{\sigma}}_{0}\ifmmode\pm\else\textpm\fi{}p$, we find $p=2.0\ifmmode\pm\else\textpm\fi{}0.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$. From the determined value of the length $\ensuremath{\lambda}=3.2\ifmmode\pm\else\textpm\fi{}0.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ cm, the linear dimensions of the microcrystals can be determined to be $\ensuremath{\delta}=1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ cm. For a thickness $d=3.8$ cm a transmission effect of almost 8 percent was observed if the magnetization was brought to within 2.5 per mille of its saturation value; more than twice this effect can be expected from the same thickness at complete saturation.