424 Nuclear Instruments and Methods in Physics Research B54 (1991) 424-428 North-Holland A synchrotron radiation microprobe for X-ray fluorescence and microtomography at ELETTRA. Focusing with bent crystals Roberto Devoti and Federico Zontone Dipartimento di Fisica, Universitri di Trieste, 34127 Trieste, Italy Claudio Tuniz ’ and Franc0 Zanini Sincrotrone Trieste, 34012 Trieste, and INFN, 34127 Trieste, Italy An X-ray fluorescence microprobe utilizing the radiation from a bending magnet of ELETTRA, the high-brilliance synchrotron radiation source being built in Trieste, has been proposed. Various focusing monochromators have been considered in order to produce a micron-size beam. Here we use ray-tracing programs to estimate the X-ray fluxes obtainable at ELECTRA with a bent crystal. The performance of the microprobe for trace-element analysis and computed tomography of microscopic biological specimens is also presented. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1. Introduction Synchrotron radiation (SR) induced X-ray fluores- cence (SRIXE) provides a powerful microanalytical technique for environmental science, biology, medicine, geology and materials science. The advantages of using focused SR for microcharacterization of materials were discussed ten years ago by Sparks [l]. A recent survey of the SRIXE method is given in ref. [2]. A SRIXE microprobe utilizing the radiation from a bending magnet of ELETTRA [3] is being proposed [4]. The aims of the project are: (1) Design and construction of state-of-the-art opti- cal systems to produce a beam of X-rays with lateral resolution of 1 km and various degrees of monochro- maticity in an energy range of 5-20 keV. (2) Development of advanced detection systems based on scanning and tomographic techniques to mea- sure the distribution of trace and minor elements with high spatial resolution. (3) Setup of specific laboratory techniques to handle microscopic specimens as cells, micro-organisms and atmospheric particulates. ELE’MRA, a third-generation high-brilliance ring, is particularly suitable for the development of a micro- beam. In addition, continuous progress is being made in mirror technology and optical design for X-ray micro- ’ Also Dipartimento di Fisica, Universita di Trieste, 34127 Trieste, Italy. focusing. The performance of a system based on bent crystal monochromators is briefly discussed in the pre- sent paper. 2. Bent crystals as hard X-ray focusing elements In the hard X-ray region focusing can be achieved by the use of different techniques: metal-coated curved mirrors [5], bent crystal monochromators [6] and multi- layer-coated optics [7]. Bragg-Fresnel lenses [8] are the most promising solution in the far future, but are still at an early stage of development. Bent crystals and multilayer optics present various advantages with respect to other focusing systems. Typi- cal acceptances of crystals and metal-coated mirrors have already been compared [9], showing that Bragg angles for diffraction from crystals are more than one order of magnitude less grazing in comparison with critical angles for mirrors in the hard X-ray region. The same applies for multilayer optics. Another advantage of bent crystals and multilayers is the partial monochro- matization of the incoming beam, which allows a lower minimum detection limit (MDL) in relative concentra- tion than continuum excitation [lo]. We performed a preliminary study on the design of a SR microprobe for X-ray fluorescence for a bending magnet at ELETTRA, considering an ellipsoidally bent crystal as a focusing element. The performance of this system in terms of spot size, energy bandpass and integrated intensity has been estimated using the ray- 0168-583X/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)