Study of the reflectivity of neutron supermirrors influenced by surface oil layers

Neutron guides made of supermirror-coated glass are important components of most neutron scattering instruments, thus their quality and possible deterioration due to various deleterious effects (e.g., surface contamination or defects) deserve careful examination. The modification of the reflectivity of supermirrors and the transmission of neutron guides due to surface contamination with hydrocarbon oil has been investigated using neutron reflectometry together with model calculations. A significant loss in the neutron reflectivity was observed for supermirrors covered with thin hydrocarbon oil films, which were confirmed in model calculations. Simulations carried out for several typical arrangements show drastic decreases in the transmitted neutron flux of neutron guides. These simulations show that determining the distortion of the beam profile (using a slit or a pin hole) enables the detection of oil contamination even in an operating neutron guide. (C) 2010 American Institute of Physics. [doi:10.1063/1.3443319]