X-ray extended-range technique for precision measurement of the X-ray massattenuation coefficient and Im(f) for copper using synchrotron radiation

We reconsider the long-standing problem of accurate measurement of atomic f orm factors for fundamental and applied problems. We discuss the X-ray exte nded-range technique for accurate measurement of the mass attenuation coeff icient and the imaginary component of the atomic form factor. Novelties of this approach include the use of a synchrotron with detector normalisation, the direct calibration of dominant systematics using multiple thicknesses, and measurement over wide energy ranges with a resulting improvement of ac curacies by an order of magnitude. This new technique achieves accuracies o f 0.27-0.5% and reproducibility of 0.02% for attenuation of copper from 8.8 4 to 20 keV, compared to accuracies of 10% using atomic vapours. This preci sion challenges available theoretical calculations. Discrepancies of 10% be tween current theory and experiments can now be addressed. (C) 2001 Elsevie r Science B.V. All rights reserved.