EXAFS (Extended X-ray absorption fine structure) refers to the sinusoidal variation of the X-ray absorption coefficient as a function of X-ray photon energy, which occurs after each absorption edge of an element and extend s for up to 1500 eV further. This phenomenon forms the basis of the analytical technique of EXAFS spectroscopy, which can be used to obtain structural information about molecules without the need for obtaining single crystals.
In fast or continuous EXAFS the intensity is sampled while the monochromator of the beamline is rotated continuously. The actual position of the monochromator can be obtained by counting the pulses from an angular encoder in parallel. The SIS3801 or the SIS3806 multiscalers are especially suited for this application, as the counters are also capable of gernating their own readout timing either from an internal timer or from an external signal like the angular encoder, i.e. the counting period can be defined in time or angular steps. As 32 (SIS3801) or 8 (SIS3806) counter inputs are available, the incident flux and a variety of other parameters can be measured in parallel after voltage to frequency conversion as well.
Steps for the measurement:
Start rotating the monochromator to scan through the energy around the absorption edge
Set the internal multiscaler readout (LNE) time interval to 10 ms e.g.
Read the intensity (from a V/F converter) and number of pulses from the monochromator angular encoder from the two corresponding scaler channels.
The main benefit is a reduction in the duration of the measurement from something like 30 minutes (without SIS3801/6) down to several minutes (with SIS3801/6.