How it Works?
Crystals do it for you
Bonse-Hart (BH) USAXS relies on the inherent rocking curve width of single crystal diffraction to determine the angular resolution, hence q-resolution, along the scattering plane, while in the orthogonal direction the beam is collimated with apertures.
This is shown schematically in the figure to the right. The incident beam from the source is conditioned by multi-bounce Bragg diffraction from a single crystal monochromator. Upon transmission through the sample, the scattering radiation is selected at each scattering angle 2q by an analyzer crystal (identical to the monochromator) which rotates about the sample. Data collection is serial (point-by-point) and detection can be obtained by a NaI point detector or alternative by an area detector to further reduce noise and eliminate parasitic scattering.
Because the scattering is exquisitely resolved in one direction only, the resulting data are slit-smeared, similar to what one sees in the Kratky SAXS geometry.
Resolution: 5 Microns
With a Cu Kα lab source, and a BH-setup with Si(111) crystal reflection surfaces, the inherent 7 arcsec resolution-width of the crystal reflection leads to a probe length resolution of 5 microns. In practice, the system is kept quite compact, since the system length increases intensity falloff in the unresolved direction. A typical configuration is contained completely in vacuum with a total path length on the order of 0.5m and collection times of about 30 minutes for scans through the direct beam (providing the resolution function, I0 and transmission) up to q = 0.1 A-1 for most soft materials.
Dedicated or add-on?
The TR-USAXS is available as a standalone instrument with or without the ability to extend the SAXS to higher q in a hybrid instrument.
It is also available as an add-on to an existing Ganesha SAXS instrument.