Detector characteristics aperture sizes

There are several advantages to a tunable filter system. First, it is unnecessary to have a multichannel detector (for single-point measurements), since only one wavelength is being selected at a time. The size of the detector is also much more flexible, since spectral resolution of the system is not a function of the detector and input aperture as it is in a classical monochromotor, but rather limited only by the functional characteristics of the filter. Second, since focusing and dispersive elements are minimized the spectrometer could be made very small. Third, the entire spectrum does not need to be obtained the random access nature of the filter allows only the spectral features required for a measurement to be made. This can be a significant advantage for routine measurements. 

The entire microprobe setup is positioned on a movable granite table. Compound refractive lenses are used for focusing to a routinely achievable spot size of 1-2 pm vertically and 12-15 pm horizontally. The intensity of the incoming, the focused, and the transmitted beam is monitored by ionization chambers and photodiodes. A miniature ionization chamber with an aperture of 50 pm diameter as an entrance window was developed at the ESRF for measuring the intensity of the focused beam close to the sample (Somogyi et al. 2003). The characteristic X-ray line intensities are detected with a Si(Li) detector of 30 mm active area, 3.5 mm active thickness, and 8 pm thick Be window placed at 90° to the incoming linearly polarized X-ray beam. Fast scanning XRF measurements (>0.1 s live time/spectrum) are possible. 

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