Neutron reflectometer with horizontal scattering geometry

Neutron reflectometry examines the way in which surfaces or interfaces reflect neutrons in order to provide information on their organization, thickness, composition and roughness. Layer stacking can be studied on a thickness scale of 1 to 500 nm (5 to 2500 atomic layers).
If the incident angle is lower than the critical angle, the material acts like a mirror and reflects all neutrons. If it is higher, only a part of the neutrons are reflected. Measuring the proportion of reflected neutrons for a reflection angle equal to the incident angle makes it possible to explore the sample in a direction perpendicular to its surface. If measurements are made for different incident and reflecting angles, the sample is explored in its surface plane.

Reflection on a plane surface (the interface between two materials)

To make the illustration clearer, angles are greatly exagerated from their actual values for cold neutrons. Note that the opposite animation shows a monochromatic setup while D17 is more often used in the time-of-flight mode.