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. 2011 Sep 1;649(1):101-103.
doi: 10.1016/j.nima.2010.12.023.

A new beamstop for microfocus X-ray capillary beams

Ulrich Englich  1 , Peter Revesz, William Miller
Affiliations

A new beamstop for microfocus X-ray capillary beams

Ulrich Englich et al. Nucl Instrum Methods Phys Res A. .

Abstract

In order to accurately measure the photon flux and to assist in aligning the beam, we have designed a modified beam stop device based on a photo diode integrated with the beam stop. The beam stop contains a small CdWO(4) crystal that completely stops the X-rays and at the same time produces photoluminescence proportional to the X-ray flux. The light is then guided to a photosensitive diode, using a flexible light pipe, to monitor the flux. With this device we achieve the goal of stopping the primary X-ray beam and simultaneously monitoring the X-ray intensity, thus eliminating the need for integrating ion-chambers into the capillary or collimator mount.

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Figures

Figure 1
Figure 1
(a) A view of the steel tube with a window cut out at the end. Just behind the opening a 0.92 × 0.92 × 5 mm CdWO4 crystal is inserted. The steel tube is flattened to firmly hold the crystal in place and reduce its profile. (b) The window is covered with a small piece of aluminized Mylar foil to prevent light from entering the fiber.
Figure 1
Figure 1
(a) A view of the steel tube with a window cut out at the end. Just behind the opening a 0.92 × 0.92 × 5 mm CdWO4 crystal is inserted. The steel tube is flattened to firmly hold the crystal in place and reduce its profile. (b) The window is covered with a small piece of aluminized Mylar foil to prevent light from entering the fiber.
Figure 2
Figure 2
The goniometer with the beamstop at the left of center, mounted in line with the goniometer phi axis. X-rays enter through the collimator from the right (here shown with an ion chamber).
Figure 3
Figure 3
A diffraction pattern of bovine trypsin (cell dimensions 55 × 55 × 106 Å3, hexagonal symmetry) taken at the CHESS F1 station (energy = 13.5 keV), showing the size of the shadow from the beamstop when moved close to the sample. The size of the shadow can be reduced by increasing the sample to beamstop distance.
Figure 4
Figure 4
The graphical analysis of the normalized transmitted X-ray flux vs. thickness of the aluminum filter shows a smooth response for both types of monitoring devices: ion chamber (black squares) and the new photodiode-coupled CdWO4 crystal (red circles). Both follow closely the ideal line described by the Beer-Lambert law (red line). Data taken at the CHESS F1 station at 13.5 keV.
See this image and copyright information in PMC

References

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