Optimization of beam line design for a pulsed-neutron reflectometer with a horizontal sample-geometry (ARISA)

The dedicated neutron reflectometer with a horizontal sample-geometry, named as ARISA (Advanced Reflectometer for Interface and Surface Analysis), was constructed at a pulsed-neutron source of the KENS in a year of 2000. The adoption of the horizontal sample-geometry enabled us to make reflectivity measurements on free interfaces such as liquid surfaces, liquid/liquid interfaces, etc., and various interfacial studies mainly relevant to soft-materials have been developed until the KENS was shotdown in March, 2006. The one of key factors for success on the ARISA is the use of thermal neutrons with the shorter wavelengths, which contributed much to the extension in accessible Qz as well as reflectivity range at the small neutron source of the KENS. The two downward beam lines with different angles are guided viewing directly a moderator surface within a geometrical restriction of the existing beam hole, and one of them was selected by using an elevation system for actual measurements. Much effort has been paid for background suppression. It was realized that specular reflectivity can be measured up to 2.3 nm-1 in Qz and down to ∼10-6 in reflectivity. (author)