Bent,
Perfect Crystal, Double Focusing Silicon Monochromator
Features
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Silicon perfect crystal double focusing monochromator
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Fixed real-space vertical focusing by segmentation.
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Optimized momentum-space horizontal focusing (in diffraction) by the
selection of silicon cut angle, thickness and bending radius.
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Monochromator design optimized for the take-off angle,
Source-Monochromator and Monochromator-Sample distances of your
application.
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5 different reflecting planes and wavelengths available at a fixed
90o take-off
angle.
Adjusting screw at top:
(115) 1.478 A
(113) 2.316 A
(335) 1.171 A |
Adjusting screw at bottom:
(331) 1.762 A
(551) 1.075 A
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- Fankuchen compression of the monochromatic beam: typical 4x
intensity gain.
- No in-pile (primary) collimation required – the monochromator acts
as its own collimator.
- Excellent characteristics for small specimen size (3 mm dia) powder
diffraction applications.
Description
The
monochromator is fabricated from 9 single crystal silicon slabs
typically* 145 x 5 x 190 mm3
that have been cut from the same silicon wafer. These blades are bent
horizontally by a 4-point bending apparatus to a radius of 10-12 m*.
In the vertical direction, the blades are arranged in a polygonal
approximation to the surface of a sphere of radius 1.76 m*. The
normal to the concave surface of the silicon slabs is at 29.8º to
the (115) axis* while the (1-10) axis is oriented vertically
The
monochromator is shown with the bending screw at the top, appropriate
for use of the (115), (113) and (335) reflections.
In
principle, all of the reflections in the [110] zone are accessible
and several of these can provide useful beams. The
first three reflections (Adjusting screw at top) are accessed with
the same monochromator orientation. The latter two reflections
(Adjusting screw at bottom) require that the monochromator be turned
over.
With
the (115) reflection at a 90⁰
take-off
angle and 3mm sample, the resolution for powder diffraction is
comparable to that achieved with a 10’ primary collimator and 10’
mosaic monochromator in a conventional (multi-detector)
diffractometer with the same take-off angle.
The
monochromator is shipped to the customer with the blades in an
unstressed condition to minimize the chance of damage in transit. It
is prepared for installation by turning the adjustment screw
clockwise 3/4 turn before the device is inserted into the
monochromator cavity.
* Actual radii, angles and dimensions are dependent on the particular installation distances and take-off angle
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