Neutron Polarization and Ferromagnetic Saturation

Abstract

The transmission of thermal neutrons through magnetized iron has been measured in its dependence upon the percentage deviation $\epsilon$ 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 $\left(\frac{n^2{p}^2{d}^2}{2}\right)f\left(\frac{\lambda }{\epsilon d}\right)$, 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 ${\sigma }_0\pm p$, we find $p=2.0\mathrm{}\pm 0.1\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$. From the determined value of the length $\lambda =3.2\mathrm{}\pm 0.3\times {10}^{-3\mathrm{}}$ cm, the linear dimensions of the microcrystals can be determined to be $\delta =1.4\mathrm{}\times {10}^{-4\mathrm{}}$ cm. For a thickness $d=3.8\mathrm{}$ 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.