More precisely: The small-angle X-ray scattering method – which has been applied by the researchers in Göttingen since 2003 – determines the spacing between lattice planes. Hereby, X-rays are deflected or scattered by the electrons of the atoms in the lattice. In accordance with Bragg's Law, the deflection angle enables the spacing between the planes to be determined.
The magnitudes of these spaces lie in a range between 0,1 and 10 nm. To obtain a measurable scattering angle, the wavelength of the radiation source used must be of the same magnitude as that of the spacing between the planes. For this reason, X-rays are required, which have wavelengths in the range between 0,001 nm and about 10 nm.
For the measurement, the samples are filled into Hilgenberg capillaries of borosilicate glass with an outer diameter of 1 mm, which are subsequently sealed vacuum-tight. The sealed capillaries are inserted into a special sample holder that is then placed in the temperature-controlled unit of the measuring equipment.
Subsequently, a Kratky camera diverts an X-ray beam with a width of about 50 μm from a copper Xray source onto the test tube. Finally, the scattered radiation is measured by means of a detector located about 1 m away from the sample. To prevent the detector being damaged, a so-called primary beam stop is fitted in the vacuum chamber, which blocks some 90% of the diverted primary X-ray beam.
Because the demand for protein measurements has increased greatly, the researchers in Göttingen decided to use a capillary flow system in 2012. In order to implement this system, Hilgenberg technicians fitted the extremely filigree test tube firmly into the sample holder by hand. Subsequently, the necessary fine tubes were glued to the ends of the capillaries on-site in Göttingen.
Apart from an improved work sequence, the flow system installed in cooperation with Hilgenberg also permits re-use of the samples after the measurement.