Number 384 (Story #3), July 28, 1998 by Phillip F. Schewe and Ben Stein|
ULTRASMALL ANGLE X-RAY SCATTERING has been used to obtain precise information on deformities in a metal crystal in the act of being stretched. How metal acquires defects when it undergoes molding or stamping is no small matter; auto makers must make one die after another, by trial and error, until the pressed part has just the right shape. Physicists from NIST, wanting to make this art of mechanical deformation more like a science, have set an aluminum sample in an x-ray beam at Brookhaven's National Synchrotron Light Source. The x rays scatter from defects in the sample. Ironically, the more widely scattered x rays provide information at the angstrom scale, whereas knowledge of the defect structures (up to 10 microns in size) must be extracted with great difficulty from the pattern of x rays scattering through very small angles. NIST's new high-efficiency, low-angle (as small as 6 arcseconds) measurements yield the best information yet of what the defect structures look like. Unexpectedly, the defects are not entirely disordered; a fraction of them lie at regular intervals. The researchers (Gabrielle Long, email@example.com and Lyle Levine, firstname.lastname@example.org) reported at the ACA meeting that their next step will be to bring these experiments to the x-ray source at Argonne, where intensities will be 100 times greater.