The expected date of release of the SAXSGUI data analysis software is Monday the 5th of November.

Hello all.

A quick link to a place I stumbled across yesterday. iTunes U. It’s a collaboration that’s been around for a while between (American) universities and Apple iTunes. The universities post some of their lectures online, for all to view, in a sort of “open university”-style.

This allows for public access to lecture series in both video and audio, on general topics such as physics, chemistry and art. Besides that, there’s also a considerable library of free music from those universities. You may think of Mozart as sung by a choir, but also singer/songwriters.

Do check it out, if only for the music (some of which is rather good). This collaboration exemplifies the belief that knowledge should be shared, a similar goal as what I hope to achieve with this weblog.

Herewith I’d like to present the results of some brainstorming on a sample holder design. This concept design is to be build soon, so if I can, I’ll make the design drawings available as well. If anyone has ideas for improvement, I’ll be happy to implement them (under the Creative Commons noncommercial sharealike license).

My reason for publishing these images is to have others save time if this sample holder suffices for their task. Many people are designing sample holders by themselves, taking up time that could just as well be spent on something more “front-line” in terms of research. I have selected the Creative Commons license, because I want to involve people in the design, and enable the use and evolution of these sample holders in research. I do not want companies to make loads of money on it, instead they can choose to supply it for manufacturing costs as an additional bonus option to their machines.

Enough of the legal considerations, on to the practical.

In my design, the sample holder conditions were:
– Easy loading of samples
– Multiple samples per sample holder
– A variable sample thickness from 0.5 mm up to 2.
– Controlled heating.

The design that I conceptualised with useful comments from Karsten D. Joensen, Jens W. Andreasen, Kell Mortensen, Martin E. Vigild and Enno Klop are depicted in the figure below:

A) shows an exploded view of one cell in the sample holder. The materials envisioned are teflon for the bolt, torque remover ring, and spacer ring, mica for the windows and an o-ring of a suitably inert material, such as Viton.
The torque remover ring purpose is to remove screw torsion on the mica windows when mounting the samples. It is not known whether this is absolutely necessary, but it could prevent creasing of the mica.
The spacer ring (inner disc-like ring) has the thickness required, and prevents the forces from becoming too large on the o-ring and sample.
The main mounting plate as illustrated, only has one sample position, but one could imagine more sample positions next or above one another. The plate furthermore has four holes through it that can support a heating wire, and a hole on the top for mounting a thermocouple. Liquid cooling is another option, but would require a slightly more bulky main plate.

B) shows a cross-section of A), which highlights the opening angle of the exit hole, and the grave in which the sample rests. The maximum angle for this model is 45 degrees, but could be made larger depending on the material of the main plate.

C) shows a cross-section of the un-exploded sample holder. A (red) one millimeter beam is drawn in for comparison purposes. The threads on the bolt are supposed to line up with that of the main plate, naturally. The sample holder main plate could be chosen thinner, for more convenient loading of the sample. In this design, it is a 1 cm. thick plate.

As said, more information on this design will follow if possible. Any comments are always welcome.

This work is licensed under a
Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.

The last time I mentioned the benefits of the PILATUS detector system. Since then, I’ve had some brainstorming sessions, and there are a few issues with the detector:

1. It looks like it is not built for use in vacuum, electronics are cooled by convection.
2. It is rather small and not square.

The first issue would mean that the detector would have to sit behind a window. Leave enough space between the detector and the window, and the air scattering would significantly reduce the benefits you had wiht the high resolution. The solution here might be to adapt the detector system, so that an external cooling system could be led through the electronics housing. In my view, it reduces complexity in a SAXS system to have as few windows in it as possible.

The second issue is of a more complex nature. The PILATUS website states that one PILATUS 100K module has an active area of 84 x 34 mm. In terms of detector systems, this is really small and non-square. Regarding the non-squaredness, a stationary single detector, positioned so that the beam falls onto one of the ends of the detector plates, would be sufficient for measuring solutions or other isotropic (randomly-oriented) systems. These systems have isotropic scattering patterns, and therefore would not require a full (square or round) detector area to be captured. For anisotropic systems, one would be very interested in capturing the entire scattering pattern.

One option to benefit from the small size is to minimize the SAXS system geometry, but this requires the use of very small pinholes. Given that the standard X-Ray generator has a source point of approx. 1mm in diameter, this would mean that you’d be cutting away most of your generated intensity, e.g. a reduction of the pinholes by a factor of 2, would cut down the beam intensity by a factor of 16. That simply is not worth the smaller size.

Secondly, the active area of the detector can be increased by tiling many 100K’s. This is indeed a good idea, but only when enough money is available. A 25×25cm detector would contain 24 100k modules, which might get rather pricey.

The third option is to move the detector, like so:

In this image, the red dot is the direct beam, and the arrows indicate the translations. Two translations are exemplified, a circular translation around the beam (A) and a lateral translation along the short axis of the detector (B).
In the case of a translation lile (A), given the fast read-out speed of the detector (100 images per second) this would mean that you could do a full circle in about 30 seconds (maximum speed), without smearing (motion blurring) over more than one pixel. Such a translation would mean that, as you go further away from the beam, the intensity would have to be corrected more and more, for the fraction of the area that the detector covers (about 1/6th in the outer regions). This method then, has an enhanced error in the outer regions. If you are only interested in analysing Guinier regions (i.e. close to the beamstop), this should not be too much of an issue.

An area with a total diameter of about 120mm could be captured with this method, using only a single detector. Measuring a half-circle would suffice, since the whole pattern can then be reflected in order to obtain the full scattering pattern. Such a motion would only take 15 seconds at maximum speed.

In case it is, option (B) has a translation that equally distributes the measurement time in each position. If a square area is to be analysed, this would mean a reduction of about a factor of three in terms of total counted intensity. The area captured by this method is equal to that of the circular translation, since the whole pattern can be reflected around the horizontal axis. This method would thus create equal errors over the entire measured area.

One can imagine many more motions like these, some highlighting the outer regions more than the inner regions and vice versa. This shows that for the price of a single detector, the options are still limitless, and the measurement times “only” increase by a factor of 3 to 6.

If intensity is that which is sought, and price would be a real limiting factor, combining a slit-collimated (Kratky-type) system with one of these detectors could be a viable solution.