Beamline description

X-Ray Fluorescence Detectors


The fluorescence measurements are performed using a Silicon Drift Detector (SDD) (XFlash 5030, Bruker Nano GmbH, Germany). This SDD has a 30 mm2 nominal crystal area, a thickness of 450 µm and resolution equal to 131 eV (@MnKa). It is equipped with a Super Light Element Window (SLEW) of the type AP 3.3.
A Zr collimator is placed in front of the detector chip to prevent the detection of photons at the edges of the crystal and to improve the energy resolution and the peak to background ratio. The presence of the collimator limits the effective active area to about 25 mm2.

To prevent the detection of photo- or Auger electrons emitted from the sample surface, the SDD is coupled with an electron trap (permanent magnet) placed in front of the end cup. Two Al apertures with respective diameters of 2.25 mm and 4.7 mm inserted at both sides of the photoelectron trap (length 4.2 mm) ensure that no parasitic line from the magnet elements will be detected, whereas the incoming X-rays are detected within the central region of the SDD sensor (3.98 mm2).
When the optimum detection of light elements (Z<14) is not necessary, the electron trap can be replaced by a 8.5 µm Be window.

The positioning of the detector-sample distance is performed using one motorized linear stage, connected to the SMC for the 7-axis manipulator and the base system.

The SDD output signal is processed by a Digital Signal Processing unit (by Bruker Nano GmbH) providing detector bias supply, pile up rejection, input/output rate meter, dead time correction using an internal “zero” peak and selectable shaping time constants in the range (0.89 – 6.1 µs). For more details see the User’s Manual of the IAEA control software.
 
In order to improve detection sensitivity for experiments in grazing incidence geometry, a three-element SDD (SGX Sensortech, UK) is currently under commissioning. The three crystals of 50 mm2 active area and 450 µm thickness each are arranged vertically along an arc with a 34 mm radius. The energy resolution is 131 eV (@MnKa). All three elements have 12.5 µm DuraBe-plus window. A long and a short collimator can be used optionally, with optimum sample-detector distance of 34 mm and 14.6 mm, respectively, considering the central sensor. The detector system is water cooled. The SDD output signal of each element is processed individually by a four-channel Digital Signal Processing unit (DXP-XMAP, XIA LLC, USA).
 
Last Updated on Monday, 08 January 2024 15:47