Low-background ultrahigh-purity aluminium window for small-angle neutron scattering using monochromatic cold neutrons

The 500 mm-diameter aluminium alloy neutron window in the SANS diffractometer SANS-J at JRR-3, Tokai, Japan, has been replaced by an ultrahigh-purity aluminium (5N-Al, >99.999%) window. Although the 5N-Al window is three times thicker than the alloy window to compensate for the lower tensile strength, the background intensity in the small-angle neutron scattering (SANS) curve was successfully decreased by a factor of 10 at the maximum. The 5N-Al window is suitable not only for large-diameter neutron windows in SANS diffractometers but also for windows in their environmental apparatus which cannot be made of single-crystal silicon or other ceramics due to their poor availability, fracture strength, processability or affinity with metallic materials.