THE SYNCHROTRON RADIATION MICROPROBE AT THE SRS, DARESBURY (UK) AND ITS APPLICATIONS

A synchrotron microprobe has been constructed at the Synchrotron Radiation Source at Daresbury (UK). This instrument is capable of analyzing at the ppm level, or, in favourable cases, at the sub-ppm with a lateral resolution of 15 μm. A beam energy of 15 keV was chosen, in order to be able to scan a wide range of analyzable elements. Focusing and monochromation of the white beam was done in a single step with a high precision ellipsoidally curved Si(111) crystal, mounted on an aluminium support. Beam spots of a few tens of microns can be made using an object slit setting of 30 mm horizontally and 5 mm vertically without further collimation. In this spot sufficient flux of 15 keV (quasi-monochromatic) X-rays is available for measuring trace elements at the femtogram level. Measurements on biological materials demonstrated the lower detection limits obtainable with micro-SXRF as compared to micro-techniques using ion-accelerators, especially for the higher Z-elements. Moreover, the much lower energy deposited in the specimen represents a major argument for prefering X-rays to ions for the analysis of radiation sensitive samples. Measurements on a geological reference sample showed better sensitivities for X-rays than protons and electrons for the higher Z-elements. © 1990.