A monitor for the spectral distribution of white synchrotron radiation

Abstract

To analyze nondestructively the elemental composition of expensive and sensitive objects pertaining to the history of art and civilization, X-ray fluorescence analysis (SYXRF) can be performed at the electron storage ring ELSA, University of Bonn, using synchrotron radiation (SR) as a powerful source of X-ray radiation. The calibration by standards is cumbersome for targets of different types, therefore, quantitative analyses should be performed by the fundamental parameter method [1]. Using known experimental and theoretical parameters, like X-ray production and absorption cross sections, the elemental abundances in thick targets can be determined from the measured Xray fluorescence intensities emitted. One basic information needed for these calculations is the spectral distribution of intensity of the exciting SR at the target position. Accelerated electrons with energies of several GeV emit a continuous spectrum of SR reaching energies possible to excite Kand/or L-shells of all elements. SR is focused in the direction of the electron motion with opening angles of about 0.15 mrad in the X-ray energy region. For one electron on an ideal orbit, the spectral and angular distribution of the SR is given by the Schwinger equation [2, 3]. In existing electron storage rings many electrons oscillating around the ideal orbit are contributing to the emitted radiation. Therefore, a quantification of the SR spectrum has to take into account this finite size and divergence of the electron beam. Calculations [4] show that the spectral distribution of SR, seen through a diaphragm of definite size, depends on the vertical position and size of the diaphragm, the effective vertical size of the electron beam rerf (FWHM of the