Beamline Phone Number:
+44 (0) 1235 778418
Principal Beamline Scientist:
Dave Allan
Tel: +44 (0) 1235 778644
E-mail: [email protected]
Email: [email protected]
Tel: +44 (0)1235 4494052
By placing attenuation in the path of the X-ray beam and reducing the number of incident photons, it is possible to ensure that the maximum count rate of the detector is not exceeded. If photons arrive at the detector at a rate faster than the electronics for the affected pixel can process them, then some of the photons will not be counted. If this happens, then the brightest reflections will not be measured accurately, and this will reduce the quality of the data.
The attenuation devices are driven by specifying the percentage transmission required. The transmission is wavelength dependent so for a given thickness of material, the percentage transmission will be greater for shorter wavelengths than for longer ones. The plot below shows how the transmission varies at different energies as the thickness of the aluminium wedge increases.
ATTENY is an aluminium wedge and, for example, at Zr (0.6889 Å) 50% of the incident beam transmission is achieved by inserting a thickness of 0.5 mm of Al into the beam. This is the thickness of the wedge when ATTEN Y is set to 10.28 mm. However, at Ag (0.4859 Å) the transmission at this setting of ATTEN Y would be 78% and at Au LIII (1.0402 Å) the transmission would be 10%.
ATTENX is a wedge made from an organic polymer and is needed for longer wavelengths and to achieve higher levels of transmsission than the aluminium wedge can provide.
The Screen19 tool is used to give an indication of how much attenuation to use.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
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