Examples of Measurement & Counting Times on FIGARO

Measurement of the surface excess (single deuterated component) or a contribution to the surface composition (selected deuterated component in a multi-component system) can be measured at low Q in air contrast matched water with an uncertainty of 2% in as little as 1 min, and useable kinetic measurements in user experiments have been carried out in as little as 1 sec.
Structural measurements over the whole Q-range (0.005-0.4 A^-1) in a D2O subphase can be measured in as little as 2 min. These counting times apply to free liquid surfaces with a surface area of at least 60x40 mm, and they compare favourably with those on the previous generation of neutron reflectometers. Examples of data of each type of measurement can be found in FIGARO's technical paper (see Publication section). In practice, however, it must be stated that the counting time depends on the scattering contrast in the surface layer, the sample environment and the instrument settings used, and typical run times are on the order of 30-60 minutes per sample.

Specular reflectivity measurements over the whole Q-range (0.005-0.4 A^-1) depend on the scattering contrast of the surface layer, the size of the solid crystal and the instrument settings used.  For typical sample cells and instrument configurations, a minimum reflected signal of 5 x 10^-7 or 1 x 10^-6 after background subtraction can be obtained for D₂O or H₂O, respectively. Without taking further measures to reduce background scattering, this limits the maximum measurable Q_z  to approximately 0.20 to 0.25 A^-1 for samples with 5-A rms roughness. Typical counting times using 80x50 mm crystals, 7% wavelength resolution and a 20-A frame overlap mirror are 45 min in D₂O, 60 min in H₂O and 90 min in a contrast matched subphase.