A new netron reflectometer (ARISA) with vertical scattering-plane geometry for studying free surface was installed at a thermal neutron port viewing an ambient-temperature water moderator at KENS. ARISA is a unique reflectomer using thermal neutrons at a pulsed spallation netron source as well as the first neutron reflectometer with vertical scattering-plane geometry in Japan. An inner iron Collimator with two beam holes and a neutron beam-line shield were installed to minimize high-energy neutrons directly coming from the neutron-target due to the shield loss produced by beam holes themselves. The inner collimator makes two independent downward beam holes with different angles, 0 deg - 0.47 deg and 1.4 deg. The neutron beam-line shield has function of an additional beam-shutter as well.
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