Vol.11 - Spring Issue 2011
New x-ray beam for x-ray microdiffraction
Xenocs is expanding its beam delivery systems product range with the GeniX 3D Micro Spot adapted for x-ray microdiffraction applications requiring a high photon density with high spatial resolutions (spot size smaller than 50 µm).
The GeniX 3D Micro Spot is available in various energy (Cu, Cr, Mo) with unique aspheric multilayer optics to achieve a spot size smaller than source microfocus size without any pinhole and with a comfortable focal distance. The tiny spot size and high photon density benefits for x-ray microdiffraction or x-ray fluorescence applications.
One application example is microbeam analysis. In collaboration with GE Sensing and Inspection Technologies, preliminary diffraction measurements on ferrous samples have been performed using the ultrafast Meteor1D detector. We are presenting the results illustrating the advantage of the GeniX 3D Micro Spot in terms of high intensity (counts/s/surface area) and low background for microdiffraction and microbeam applications.
The GeniX 3D Micro Spot versions have been developed for x-ray micro-analysis requiring a spot size smaller than microfocus sources with a comfortable divergence (in the order of 1°). This is the case for microbeam stress analysis or microdiffraction on small and strongly curved sample areas.
The Micro Spot optics
Xenocs Micro Spot optics are ellipsoid of revolution optics collecting the flux emitted by a point source located at a foci of the ellipse and focusing this beam on the second foci with a demagnification of source size at the focal point. This configuration is illustrated on Figure 1. This demagnification set-up is in a sense the reverse of the traditional configuration where the optic is placed closer to the source to achieve a magnification of source size such as in single crystal applications.
The demagnification set-up efficiency, i.e. the capability to reduce the spot size is directly related to the shape precision of the mirror (i.e. the slope error). Our FOX 3D manufacturing technology enables to manufacture optics producing a spot size smaller than 30 microns while using a 40 microns source preserving a high photon counts. Figure 2 is a spot size measurement achieved with a 40 µm/14W Chromium source coupled to a FOX 3D CR 30_8 optic.
The GeniX 3D Micro Spot model is available in various energy (Cu, Cr, Mo) providing a tiny spot size without any pinhole and with a comfortable focal distance.
Table I is illustrating the measured performance for Copper radiation comparing a GeniX 3D Cu Micro Spot to a Rotating Anode Generator with a FOX 2D CU 25_25 optic using a collimator with a pinhole placed at the focus. Despite operating a source power significantly lower compared to the RAG set-up, the GeniX3D Cu Micro Spot is providing equivalent useful flux for the same spot size (20 μm FWHM). This results from the use of a higher divergence X-ray optic (1°) and an optimum optical coupling for this small spot application. The GeniX 3D Cu Micro Spot reveals a high performance solution for microbeam analysis with the advantage of being a low cost of ownership, low maintenance solution.
Table I – Performance of a GeniX 3D Cu Micro Spot compared to a rotating anode generator with a FOX 2D 25_25 optic
| Source | Optical Configuration | Spot size | Flux (Mph/s) | Divergence (mrad) | Sample environment |
|---|---|---|---|---|---|
| 100 µm 800 Watts RAG 40kV,20mA |
FOX 2D CU 25_25 optic Full beam |
120 µm FWHM |
500 | 6 | Sample placed behind pinhole |
| 100 µm* 800 Watts RAG 40kV,20mA |
FOX 2D CU 25_25 optic With 20 µm pinhole |
20 µm* | 20 | 6 | Sample placed behind pinhole. Spot size is 40-50 µm at 10 mm |
| GeniX 3D Cu Micro Spot 30W/40µm |
FOX 3D CU 30_8 optic | 20 by 25 µm FWHM | 30 | 17 | Few centimeters sample clearance |
Preliminary measurements for microbeam stress analysis
GE Sensing & Inspection Technologies has developed a microdiffraction system - the SEIFERT XRD 3003 Stress Analyzer µBeam - designed for measuring stress on very crucial spots of parts such as injectors, gears, micromechanics etc. The microbeam enables highest local resolution and correct residual stress analysis on strongly curved surfaces.
Preliminary tests were conducted at XENOCS in order to verify the capability of the GeniX 3D Cr Micro Spot for such critical applications, in collaboration with GE Sensing & Inspection Technologies.
Diffracted intensity measurements have been performed at XENOCS with a laboratory test bench set-up on a standard ferrous sample. Measurements were done in air with a sample spinning using the GE ultrafast Meteor1D detector. 100 second measurements revealed a very high intensity peak while using a 30cm air path. By using the GeniX 3D vacuum evacuated beampath the measurement will be 3 to 4 times faster with the same data quality. A very low background was achieved by a combination of the low counting noise of the Meteor1D detector and the monochromatic beam.
In conclusion the diffracted intensity achieved with the GeniX3D Cr Micro Spot is few times higher than standard solutions using standard sealed tube with capillary optics.
‘‘Especially for microbeam stress analysis on the some 10µm scale GeniX Cr Micro Spot is a set-up with currently unique performance, at best in beam shape, intensity, peak-to-background ratio, maximum 2Theta diffraction angle and even sample clearance’’ says Dr Rainer Stabenow from GE Sensing & Inspection Technologies.
