1063-7850/01/2701- $21.00 © 2001 MAIK “Nauka/Interperiodica” 0011 Technical Physics Letters, Vol. 27, No. 1, 2001, pp. 11–13. Translated from Pis’ma v Zhurnal Tekhnicheskoœ Fiziki, Vol. 27, No. 1, 2001, pp. 24–30. Original Russian Text Copyright © 2001 by Mazuritsky, Soldatov, Lyashenko, Latush, Kozakov, Shevtsova, Marcelli. As is known, both perfect and mosaic crystals are used for separating monochromatic X-rays with ener- gies ranging from a few hundreds to tens thousand of electronvolts. In the case of virtually point emission sources, it is expedient to employ either the classical focusing X-ray optics based on cylindrically bent crys- tals proposed by Johann [1], Johansson [2], and Cau- chois [3], or the more recent schemes based on spheri- cal and toroidal geometries of the bent crystallographic planes [4, 5]. Some analytical problems solved by method of elec- tron-probe X-ray microanalysis (EPMA) require instruments possessing a high spectral resolution (λ/∆λ) together with sufficiently large signal intensity (brightness). The existing monochromators cannot simultaneously provide for both. It is the usual practice to compromise between the necessary resolution level (related to small reflecting area of a crystal analyzer) and acceptable aperture of the diffractor. However, attain- ing a sufficiently high resolution [λ/∆λ ~ (1–5) × 10 3 ] in the schemes with bent crystals of any type necessar- ily imposes certain limitations on the reflecting crystal surface area, thus determining the spectrometer bright- ness limit. Previously [6], we proposed a new algorithm and developed a computer program for modeling the dif- fraction zones and reflecting surfaces of a bent crystal monochromator of any type (cylindrical, spherical, tor- oidal, etc.) employed in the schemes of focusing on the Rowland circle. For a given resolution parameter, this program determines the shape of a reflecting crystal surface corresponding to the Bragg equation (Bragg’s diffraction zone), the optimum curvature parameters, and the diffractor crystal size. Recently, we proposed for the first time a model [7, 8] and described a mathematical scheme [9] of a high- brightness stepped-crystal X-ray diffractor capable of providing a high spectral resolution at a constant angu- lar width of each step. In an electron-probe X-ray microanalyzer, the primary characteristic X-ray radia- tion generated within a microscopic sample volume enters the spectrometer chamber. Scanning over the wavelength spectrum is carried out by simultaneously moving the bent crystal (diffractor) and a detector of the crystal-monochromated radiation. In the proposed scheme, the radiation source, the crystal apex, and the input window of the detector are situated on the focus- ing circle. The optical scheme of a spectrometer chan- nel for the EPMA instrument is described in more detail in the monograph [10]. Figure 1a illustrates the principle of spectral analy- sis and the scheme of focusing of the crystal-mono- chromated X-ray radiation. The radiation source S and detector D occur on the focal circle (Rowland’s circle), the third point representing the diffractor apex located at the middle of the central step. In this study, we have used a special shape of the reflecting crystal (Fig. 1a) with a stepped pseudocylindrical surface characterized by a constant angular size of steps in the focal circle plane. Each step represents a part of the cylindrical sur- face with a constant radius, onto which a bent (002) mica crystal is glued. The central step has a bending radius equal to doubled radius of the focal circle. The bending radii of the following steps decrease with increasing distance from the diffractor center. The sym- metry axes of all the cylindrical surfaces coincide with the vertical axis passing through point O perpendicu- larly to the focusing circle. The algorithm for calculat- A New High-Brightness Stepped-Crystal Diffractor for X-ray Microanalysis M. I. Mazuritsky*, A. V. Soldatov*, V. L. Lyashenko*, E. M. Latush*, A. T. Kozakov*, S. I. Shevtsova*, and A. Marcelli** * Faculty of Physics, Rostov State University, Rostov-on-Don, Russia ** LNF, INFN, Frascati, Italy e-mail: mazurmik@icomm.ru Received August 21, 2000 Abstract—An electron-probe X-ray microanalyzers, the characteristic X-ray radiation is generated within a small volume of sample and the emitting surface area is on the order of 1 μ m 2 . For a distance to analyzer of approximately 0.5 m, this small emitting area can be considered as a point source. Practical implementations of the electron-probe X-ray microanalysis (EPMA) require a high spectral resolution and sufficient intensity. The existing monochromators cannot simultaneously provide for both. A prototype of the new high-brightness stepped-crystal diffractor for EPMA, based on four cylindrically bent (002) mica crystals, has been constructed and tested. © 2001 MAIK “Nauka/Interperiodica”.