Choosing the sample position

In transmission mode the sample can be positioned either in front of the X-ray tube or the detector. Both configurations have their pros and cons which are listed below.

IN FRONT OF THE TUBE

+ Stable beam footprint

+ Easier to align

- High dose rate

- Samples that are smaller than the tube aperture cut the intensity

- The spectral fine structure sensitive to the aperture masking

Good for radiodurable materials, standard powder/foil samples, complex sample environments, EXAFS

IN FRONT OF THE DETECTOR

+ Low dose rate

+ Allows simultaneous use of fluorescence detector

+ Smaller beam spot

- Beam footprint moves during the scans

- Difficult to align, especially small samples

- Problematic for low Bragg angles due to beam cutting

Good for liquid, organic and biological samples, low concentrations