Jim Pflugrath wrote:
In addition to reducing the beam divergence, you may wish to use a smaller beam size by using a smaller collimator or making the slits smaller. A smaller crystal can also help to spatially separate the Bragg spots as can moving the detector closer to the crystal. Yes, closer to the crystal. This is not intuitive, but arises since modern homelab beams are not parallel but are diverging from a focal point near the sample position. It is just something else you may wish to try.
But the pattern is also diverging from a point at the sample? I'm guessing the focus point is somewhere between the crystal and the detector, so by moving the detector closer you are better approximating "focus on the detector" rather than "focus on the crystal"? With a home source one probably has room for a Huber goniometer with arcs, or better yet one of those goniometers that allows rotation up to 90* about a point at the crystal, so the crystal doesn't move out of the cold stream as you rotate. One can also cheat on the mosaicity during integration by fixing it at a small fraction of the true mosaicity. This is called "cutting off the wings" or more euphemistically "peak height sampling". The accuracy will suffer, but not as much as you might expect- probably because if spot profiles are pretty similar, the the height at peak is a good measure of peak volume. eab
