The neutron transmission of single-crystal sapphire filters

The wavelength dependence of the transmission probability of a beam of neutrons through super optical quality single-crystal sapphire at room temperature has been measured. The measurements extend over the neutron wavelength range 0.05-1.2 nm. Sharp dips in the transmission caused by Bragg reflection are not found. The data below the dip around 0.2 nm in the cross section have been fitted to a function that accounts for multiphonon scattering. Measurements performed on single crystals with increased lattice distortion (or mosaic spread) show an increase in the cross section at long wavelengths. The attenuation of room-temperature Al₂O₃ is not significantly different from that for liquid-nitrogen-cooled MgO.