SSRL end of run form

Collecting good polarized EXAFS data on single crystal samples for both transmission and fluoresence is difficult because of Bragg diffraction from the sample, which changes the x-ray absorption in the sample. Usually one collects the data at a series of angles, and then combines the data to overcome this issue. For the bilayer CMR manganites we are studying, we have very thin oriented single crystals (mounted over a hole in a larger piece of the same single crystal material); however our first attempts to obtain transmission data (2+ years ago at the APS) failed because the Bragg spikes were too large.
Since then we have been using fluorescence data collection which is time consuming and has poorer data quality than for transmission. Last summer together with A. Mehta we showed on a diffraction beamline, that the problems in the transmission EXAFS were indeed caused by a number of Bragg diffractions; further we showed that oscillating the sample about vertical and horizontal axes, effectively averaged out the Bragg spikes if the oscillation angle was large enough (+- 2 deg) - we have now designed a wobbler to rotate the samples by a few degrees about horizontal and vertical axes (while the sample is in a He cryostat) and obtained the first good transmission data on one of the bilayer samples La(1.28)Sr(1.72)Mn2O7. Our preliminary data
reduction indicates consistent data. We also collected some fluorescence data using the same
method.