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Neutron Reflectometer (GANS)

Like Triax, the NR/GANS is the only instrument of its kind stationed at a university campus. This instrument employs a vertically focusing PG monochromator providing neutrons of 2.35 wavelength. The scattering geometry is in the horizontal plane, so the sample is placed vertically. Four slit assemblies with variable slit sizes allow variable collimation. This allows for variable resolution for a wide variety of studies of polymer films and interfaces. The instrument can also be used with a neutron polarizer and analyzer to carry out neutron spin analysis reflectometry for investigations of magnetic thin films and interfaces. The dynamic range of this instrument of >106 is competitive with the other in national lab based neutron reflectometers in the USA.

Neutron reflectometry (or glancing angle neutron scattering) gains its unique capabilities by implementing narrow slit masks separated as far as the geometry will allow to strongly limit the divergence of the incident neutron beam. Then by using a highly accurate motorized control, the detector arm can be driven over a very small range of angles about the straight through direction and measure variation in the scattered specular intensity. It is then possible to apply a model based analysis to determine the depth profile of the sample under study. The scales of interest are not those of inter-atomic distance but rather those on the scale of nanometers . The principle is not terribly different from the classic oil on water problem whereby the thickness of the oil layer can be determined by reflection of light (optical beam). Here we are interested in the types of materials that interact with neutrons strongly which allows for information that is not accessible through other techniques, i.e. studies of magnetic films or hydrogeneous materials. This measuring technique has become a powerful tool in material science for studying surfaces and interfaces on a nanometer scale with scientific applications to surface chemistry, solid thin films, polymers, layered materials, nanostructures, and surface magnetism.

The NR/GANS is presently undergoing an upgrade similarly to the one Triax underwent in 2005 in that the motor drivers and interface are being modernized. This instrument will be controlled by the SPEC two-axis software and is expected to be fully operational later in 2009.

Irradiation facilities
Neutron Reflectometer -- Sample is positioned vertically, the scattering plane is horizontal. It is the only instrument of its kind on a university campus.
  • Vertically focusing monochromator: PG (002), vertically focusing, mosaic width 1.3
  • Wavelength: 2.35
  • Wavelength resolution: 1.5% Δλ/λ
  • Beam size (continuously variable): 0.01x70 mm2 to 12x70 mm2
  • Q-range: 0.02 to 4.00 nm-1
  • Q-resolution (variable with slit width): 0.02 to 0.20 ΔQ/Q
  • Monochromator-to-sample distance: 1.9 m
  • Sample-to-detector distance: 1.2 m
  • Detector: 3He-proportional counter
  • Angular range for detector: 0 to 95
  • Spin-polarized capability (supermirror, flippers, etc.)
  • Variable temperature and field sample environment