Elliptical neutron-focusing supermirrors with Ni-P-plated Al-Si alloy substrates for multi-incident-angle neutron reflectometry.

This study introduces a novel approach for multi-incident-angle neutron reflectometry utilizing metallic elliptical supermirrors to enable the simultaneous focusing of two distinct neutron beams. The supermirror is composed of depth-graded NiC/Ti multilayers and functions as a reflector for grazing-incidence neutrons. Two mirror pairs consisting of precise elliptical supermirrors with diamond-machined and polished Ni-P-plated Al-Si alloy substrates were fabricated. Thermal deformation is minimized by this Al-Si alloy, which has a thermal expansion coefficient similar to that of Ni-P. The focusing performance was evaluated using the SOFIA neutron reflectometer located at BL16, Materials and Life Science Experimental Facility, Japan Proton Accelerator Research Complex. The experimental results confirmed that the two neutron beams converged to a single spot with a full width at half-maximum of 0.26 mm. Optimizing the simultaneous focusing of dual beams presents technical challenges that warrant further investigation in the future.