- For home-lab systems
- For synchrotrons
Schematics showing the difference between the conventional two pinhole configuration and the scatter-free Scatex pinhole setup. Due to a strongly reduced scattering background of the Scatex pinhole no anti-scatter pinhole is required anymore!
SAXS setup with a typical 3-pinhole collimation system
The illustration clearly shows that even with an antiscatter pinhole the beam stop needs a large diameter due to the parasitic aperture scattering. Using SCATEX pinholes instead, the scatter guard becomes dispensable and the minimum beam stop diameter decreases. Thus, SCATEX pinholes enable a higher resolution and photon flux.
SCATEX - Incoatec´s scatterless pinholes
Parasitic scattering caused by apertures is a well-known problem in X-ray analytics, which forces users and manufacturers to adapt their experimental setups to this unwanted phenomenon. Increased measurement times due to lower photon fluxes, a lower resolution caused by an enlarged beam stop, a larger beam defining pinhole-to-sample distance due to the integration of a scatter guard and generally a lower signal-to-noise ratio lead to a loss in data quality.
A reduction of parasitic aperture scattering is possible with scatterless slits. However, since the noise signal is generally still too high, synchrotron facilities, for example, are required to further use antiscatter guards. Furthermore, (scatterless) slit systems suffer from the rectangular beam shaping which increases the beam stop size by at least 41.4% (corresponds to √2) compared to a circular beam shaping pinhole. Thus, beam definition with pinholes is advantageous as it enables a considerably higher resolution.
The new SCATEX pinholes produce almost no parasitic scattering and overcome the aforementioned problems.
Main SCATEX features:
- Germanium pinholes for lower and Tantalum pinholes for higher photon energies
- available sizes: 20-2000 μm
- strongly reduced parasitic aperture scattering
- resolution and photon flux enhancement
- easier and faster pinhole alignment
- no scatter guard needed
- system size shrinks
- data quality improves
Detector images and corresponding count rates around the beam stop for 25%, 50% and 75% of the primary beam intensity passing the pinhole for a conventional and a SCATEX pinhole. The ordinary pinhole shows a considerable count rate around the beam stop. In contrast, the signal of the SCATEX pinhole is dominated by air scattering.
SAXS image and scattering intensity of a rat tail tendon measured with a 3-pinhole high-resolution NANOSTARTM and a modified 2-pinhole NANOSTARTM equipped with SCATEX pinholes. The resolution of both setups is very similar, but the setup with SCATEX pinholes gives a significantly higher scattering intensity.
SCATEX pinholes for SAXS home-lab systems
Typical SAXS instruments in the home-lab have a 3-pinhole collimation system where the first two pinholes define the beam size and divergence and the third aperture (antiscatter pinhole) absorbs parts of the parasitic scattering. SCATEX pinholes are basically scatterfree as the parasitic scattering signal is below the detection limit of the instrumentation throughout the experiment. In contrast, conventional, commercially available Pt/Ir pinholes cause a two orders of magnitude higher parasitic signal, which is especially high when the maximum of the intensity distribution of the primary beam hits the pinhole edge at Ipass/Itotal=0.5.
Corresponding detector images of the parasitic scattering clearly show the difference between a SCATEX and a conventional pinhole. The latter shows parasitic aperture scattering deep into the q-space, thus overlapping potentially valuable measurement data. SCATEX pinholes allow a significant improvement of SAXS instrumentations as the number of necessary pinholes can be reduced while simultaneously enlarging the beam defining pinhole size. Comparative measurements of a rat tendon were performed using, on the one hand, a 3-pinhole high-resolution NANOSTAR of Bruker AXS and, on the other hand, a modified NANOSTAR with only two SCATEX pinholes. The I(q)-plot shows that both setups have a very similar resolution. However, the scattering intensity of the SCATEX 2-pinhole setup is considerably higher. Thus, data aquisition of comparable quality to typical 3-pinhole instruments is much faster with the new SCATEX pinholes.
Detector images of the parasitic aperture scattering behavior at 8 keV for the different pinholes. Note that the measurement time for the SCATEX pinhole was 10 times longer than for the other tested apertures.
Scattering intensity vs. q-plot. Data are corrected for respective exposure times and normalized to the primary
beam photon flux and to the solid angle.
The parasitic scattering of various apertures was tested at position S5 and S6 at 13 keV.
Standard beam setup:
S5 - beam defining aperture position
S6 - scatter guard position
The data of the scattering intensity vs. q-plot is normalized to the number of summed up pixels.
SCATEX pinholes for synchrotrons
Synchrotrons provide higher photon fluxes and higher resolution compared to home-lab instrumentations. Thus, apertures used at beamlines need to be of higher quality in order to guarantee a better performance.
At the PTB four-crystal monochromator beamline at BESSY II various apertures were tested at 8 keV with a typical photon flux in the range of 4·109-4·1010 ph/s. The tested apertures were aligned centric into the primary beam to allow a maximum photon flux. The circular beam stop with a diameter of 5 mm absorbs the primary beam, whereas the signal of the parasitic aperture scattering is recorded by the Pilatus 1M detector around the beam stop.
The following apertures were compared: 1) a Cu foil with 500 μm pinhole, 2) a commercially available 500 μm Pt/Ir pinhole and 3) a 520 μm SCATEX pinhole made of Germanium. The detector images have shown that even with a 10 times longer measurement time the SCATEX pinhole causes much less parasitic scattering intensity and scatters much less into the q-space. Furthermore, the scattering pattern of SCATEX is circular, thus showing the high overall structural quality of the pinhole.
The quantitative analysis (scattering intensity vs. q-plot) shows that SCATEX pinholes produce 2-3 orders of magnitude less parasitic scattering and scatter much less into the q-space. The measured parasitic signal was integrated concentrically around the beam stop and normalized to the photon flux upstream of the tested aperture.