Efficient Tunable X-ray Monochromator for Diffraction X-ray Tubes

V. SBARATO; D. PEREZ; JUAN JOSÉ LEANI; F. COMETTO; SÁNCHEZ, HÉCTOR JORGE

Girona

Conferencia; International Conference on Total Reflection X-Ray Fluorescence Analysis and Related Methods (TXRF2019).; 2019

Universidad de Girona

Conventional X-ray fluorescence analysis (XRF) is a powerful instrumental technique for elemental quantification of samples with a wide range of matrices coming from industry, medicine, biology, environmental, archaeometry, etc. The continuous part of the X-ray tube excitation beam is mainly responsible of the high background in XRF spectra which restricts the detection limit to a few ppm (w/w). A possible strategy to reduce that background is the monochromatization of the excitation beam with a crystal monochromator. In this case, the optimization of the system components is strongly required to obtain the highest excitation count rate over the sample, since it is considerable reduced by the short energy band pass of the monochromator. In the present work a Si(111) crystal monochromator improved by an X-ray Beam Guide (BG) has been developed. The BG is composed of several thin curved steel plate reflectors placed together and separated by spacers [1]. Inside the gap, photons are transmitted by total reflection toward the crystal. To increase the X-ray transmission of the BG, thin gold layers has been deposited over the metallic plate reflectors. The BG produces a low divergence beam in the symmetry plane of the optical system ideal to fulfill the Bragg conditions on the Si(111). In this way, the design of the monochromator is compact keeping a high photon flux at the output thanks to the wide acceptance solid angle of the BG. The monochromator has been employed to select x-ray photons from the continuous part of a 3kW Mo X-ray diffraction tube. In the present work the performance of the monochromator was evaluated with special emphasis on the energy resolution and photon flux rate. The spectrometer was successfully used to selectively excite the subshells of a pure rhenium sample which we will apply to measure x-ray emission probabilities [2]. In addition the optical system gives us the possibility to run experiments of Resonant Inelastic X-ray Scattering (RIXS) with our conventional x-ray source [3]. [1] R.D. Perez et al., Nucl. Instr. & Meth. B 440: 48-53 (2019).[2] H.J. Sánchez et al., Rad. Phys. Chem. 48: 701-706 (1996).[3] J.J. Leani et al., Spectrochim. Acta Part B. 154: 10-24 (2019).