Iron-germanium multilayer neutron polarizing monochromators

A new type of thermal neutron polarizing monochromator, consisting of alternate thin layers of iron and germanium, has been constructed and tested. Bragg reflection from such artificial `crystals' in the fully magnetized state yields a highly polarized beam with high reflecting efficiency (~0.84) for the reflected spin state. These multilayer monochromators have the additional advantage that higher orders in the reflected beam are almost completely suppressed. Since d spacings are typically large (~100 Å), they produce a broader wavelength distribution than conventional single-crystal polarizing monochromators. Nevertheless, there are many applications where wavelength resolution is of secondary importance and the large gain in intensity (~40-fold) over conventional polarizing crystals can be a considerable advantage. Multilayers can also be used to advantage in combination with good monochromating crystals such as pyrolytic graphite or beryllium to produce polarized beams of high intensity and good wavelength resolution.