X-Ray Diffraction at Sonoma State University X-Ray Diffraction at Sonoma State University X-ray Diffraction is alive and well at Sonoma State. The instrument and sample preparation area were moved to the Keck Laboratory before the Darwin remodel gutted our old home. In the Keck we have rapid access to the elemental analysis feature of our SEM/EDX.
As a tribute to the people instrumental in the early days, their description is retained below with updated information. John Dunning still enjoys running difficult samples of all types.
The X-Ray lab at Sonoma State University is available to students in the departments of Physics & Astronomy, Geology, and Chemistry for personal and proprietary work. Local companies often contract with us for X-ray work, which allows students to gain valuable laboratory analysis experience.
Our lab is equipped with a Rigaku D-Max 1000 diffractometer (right), Datascan
3.4 controller software, and a Pentium 3 computer running the
latest XRD data analysis software. The JADE 6.5+ software package is an almost unbelievably powerful analysis program. Its search/match engine can, in many cases, isolate four or more components in a mixture in minutes. Pattern indexing must be experienced to be fully appreciated. Our data base is current through set 54 of the Powder Diffraction File from the International Centre for Diffraction Data (September 2004 release).
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| (Above) Rigaku X-Ray Diffractometer showing Lucite shielding and front control panel. | (Above) Our sample prep room contains a photomicrograph, drying oven, polarized microscope, several interesting posters, a small mineralogical library, and the very low-tech mortar and pestle for grinding samples. |
Put simply, the phenomenon of diffraction occurs when penetrating radiation, such as X-rays, enters a crystalline substance and is scattered. The direction and intensity of the scattered (diffracted) beams depends on the orientation of the crystal lattice with respect to the incident beam. Any face of a crystal lattice consists of parallel rows of atoms separated by a unique distance (d-spacing), which are capable of diffracting X-rays. In order for a beam to be 100% diffracted, the distance it travels between rows of atoms at the angle of incidence must be equal to an integral multiple of the wavelength of the incident beam. D-spacings which are greater or lesser than the wavelength of the directed X-ray beam at the angle of incidence will produce a diffracted beam of less than 100% intensity.
Our diffractometer utilizes a powdered sample, a goniometer, and a fixed-position detector to measure the diffraction patterns of unknowns. The powdered sample provides (theoretically) all possible orientations of the crystal lattice, the goniometer provides a variety of angles of incidence, and the detector measures the intensity of the diffracted beam. The resulting analysis is described graphically as a set of peaks with % intensity on the Y-axis and goniometer angle on the X-axis. The exact angle and intensity of a set of peaks is unique to the crystal structure being examined. In a multi-component mixture, confusion can arise when two or more components have a peak in the same, or nearby, location on the X-axis. It is for sorting out these mixtures that a good search/match engine or a search method becomes most important. The X-Ray diffraction method is most useful for qualitative, rather than quantitative, analysis (although it can be used for both).
Jade also accepts information on the elements present and/or chemical structure. For example, element composition data can be obtained separately using X-ray fluorescence. The combination of elements present and crystal structure information usually provides unique identification so long as the compound is in the PDF file.
This instrumentation is a pleasure to use in many research endeavors. The X-ray laboratory program is available to students through the following courses:
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| Ron Leu | Kathy Blum | Tim Cope | Dr. John Dunning |
| Geology Technician and all-around fix-it guy (retired). | Born-again XRD addict (graduated). | has apparently been running all sorts of radioactive equipment with the doors down....(graduated). | Director of the X-ray Lab |
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created by Tim Cope last updated 2005-01-01 by JST |
