Basic XAS setup

Basic XAS Experiment:
Ionchamber for I0 → Vacuum Sample Cross → Ionchamber for I1

EXAFS scan of the Cu foil in a continuous mode.

Transmission mode

This mode is mostly used for highly concentrated samples (> ca. 1 wt. %).
Two ionization chambers are used for the detection of the incident I0 and transmitted beam intensity I1 .
Next, the absorption coefficient is calculated:
\mu d = ln \frac{I_0}{I_1}
With 3 ionization chambers it is possible to measure two spectra for the sample and the reference simultaneously.
At P64 the continuous monochromator + undulator scans are implemented.
So, the time for each EXAFS scan is reduced down to 1-5 min.

Fluorescence mode

If the sample is highly diluted or the transmission mode is impossible for some reason the fluorescent mode can be used instead.
Here, the absorption coefficient is measured via the ratio of the fluorescence signal If and I0 :
\mu = \frac{I_f}{I_0}

If the fluorescence energy is in the range of 4-12 keV and the concentration of the element in the sample is not less than 100 ppm, the optimal choice would be to use the Passivated Implanted Planar Silicon (PIPS) Detector (Canberra) . EXAFS scan still can be done in 1-5 min.

For lower concentrations and/or higher fluorescence energies the 100 pixel High-Purity Germanium detector can be used.

100 pixel High-Purity Germanium Detector


Manufactured by Canberra GmbH

Pixelated high-purity Germanium crystal

10 x 10 pixel array, 5 mm x 5 mm pixel size

Crystal thickness: 7 mm

Maximum count rate: 350 kHz at 18 keV (per channel)

Resolution: ≤ 260 eV at 6 keV and 100 kHz

Use of a “grid collimator” to cover border areas between neighbouring pixels to avoid “crosstalk” effects

Mask material: Aluminium-covered Titanium