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Calibrating X-ray Powder Diffraction Data at the Stanford Synchrotron Radiation Laboratory

Here I am at the end of the 2007 SULI internship with my adviser
Sam Webb.

The participants of the 2007 SLAC SULI

During the summer of 2007, I participated in a Science Undergraduate Laboratory Internship at the SLAC National Accelerator Laboratory . I worked at the Stanford Synchrotron Radiation Laboratory and my advisers were Sam Webb and Apurva Mehta. During the internship, I worked on a program to calibrate and reduce x-ray powder diffraction data.

A typical diffraction pattern. This image is being viewed with
the Area Diffraction

X-ray powder diffraction is a method of imagining crystals with x-rays. The diffraction pattern that comes from the crystal are concentric rings and the ring spacing can be used to infer the crystalline structure of the material.

In order to analyze the diffraction data, you have to convert from the CCD image of the diffraction pattern to physical scattering angles. This mapping requires knowledge of the detector geometry. In particular, the imaging detector can often be somewhat rotated, changing the observed circles into conic sections.

The detector geometry is typically computed using a calibration source with a known diffraction pattern. I wrote a least-squares fitting algorithm that can calibrate the diffraction detector by fitting a known calibration source. I then wrote code to uses the calibrations to perform a radial integral of the sample data which can be used to measure the diffraction peaks.

A screenshot of the calibration tab of the Area Diffraction

I continued working on this project during my senior year of college as a senior project. I added many features to the code such as an graphical pixel-masking feature, a macro language for automating the program, and a detailed manual which describes how to use it.

The program is called the Area Diffraction Machine, and it has a robust graphical user interface which allows the program to be adopted by a general audience of x-ray diffraction scientists. The code is released under the GNU GPL, and is hosted on Google Code. At the end of my SULI internship, I wrote a research paper describing my work that you can read here.

For my work, I was awarded at the end of the summer the Ernest Coleman Award for Scholarship and Citizenship: > The award, named after one of the first directors of the SULI program’s predecessor, is nominated by the summer interns themselves. The recipient is chosen based not only on scientific achievement, but also on the support and help given to other interns. And Lande is no exception. > > “He’s been fantastic,” beamed SLAC beamline scientist Sam Webb, who mentored Lande’s summer project. “He’s accomplished twice as much as we expected [from here]

A picture of me receiving the Ernest Coleman Award for Scholarship
and Citizenship.

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