Patent Number: 
Section: description

A preferred embodiment of the present invention will be explained by referring to figures. FIG. 1 is a block diagram of an optical device for small angle scattering system relating to an embodiment of the present invention. As shown in FIG. 1, the optical device for small angle scattering system of the present embodiment has an X-ray source 2, a multilayer mirror 1, and a first, second, and third slits 4, 5, 6. The X-ray source 2 uses an X-ray generator of a high output that radiates X-rays from a pointed focus. The multilayer mirror 1 is constituted of a first reflection part 1a and a second reflection part 1b that are orthogonal to each other. The first and the second reflection parts 1a, 1b for use in the present embodiment have a multilayer structure. As shown in FIG. 4, layers 11 of a material having a large atomic number (for instance, nickel Ni, tungsten W or platinum Pt) and layers 12 of a material having a small atomic number (for example, carbon C or silicon Si) are alternately laminated on a surface of a substrate 10. Each layer 11, 12 has a thickness of several to dozens nm, and is formed at a period of 100 to 200 layers. Additionally, in consideration of the effects due to X-ray refraction at each layer 11, 12, each layer 11, 12 is inclined by a predetermined angle with respect to a surface of the substrate 10. Furthermore, each reflection part 1a, 1b is curved in the same elliptic face so as to converge reflected X-rays on one point. The X-ray source 2 is arranged at one focal point A of the above-noted multilayer mirror 1. A distance L2 from the center of the reflection faces of the multilayer mirror 1 to another focal point B (convergent point of reflected X-rays) is set so as to make a convergent angle xcex8c of X-rays at the focal point B almost twice as great as a divergent angle xcex4 of the multilayer mirror 1 (in other words, full width at half maximum of the peak of a rocking curve). This setting may be achieved by adjusting the structure of the multilayer mirror 1, for instance, the elliptical face shapes, materials, and multilayer structures. By such a setting, a distance L1 from the center of the multilayer mirror 1 to the X-ray source 2 is made sufficiently shorter than the distance L2 from the center to another focal point B (L1 less than  less than L2). For example, it is assumed that the divergent angle xcex4 of X-rays reflected at the multilayer mirror 1 is 0.05xc2x0, and the solid angle xcex1 of incident X-rays a to the multilayer mirror 1 is 0.27xc2x0. The distance L1 from the center of the multilayer mirror 1 to the X-ray source 2 is assumed to be 250 mm. When the distance L2 from the center of the multilayer mirror 1 to the focal point B (convergent point) is set at 700 mm, the convergent angle xcex8c of the reflected X-rays b becomes nearly twice as great as the divergent angle xcex4 as shown in the following formula. Thus, a preferable arrangement may be obtained. xcex8c=xcex1xc3x97L1/L2=0.27xc3x97250/700≈0.096≈2xcex4 The first and the second slits 4, 5 are provided to prevent the X-rays B reflected at the multilayer mirror 1 from diverging. The third slit 6 shields parastic scattering from the multilayer mirror 1, and is provided near the convergent point B of X-rays. It is preferable to use a quadrantal slit having slit widths that are variable in two axial directions, for the third slit 6. It is preferable to arrange a sample S at the convergent point (focal point B) of the X-rays b reflected at the multilayer mirror 1, and an X-ray detector 3 is installed at the downstream thereof. An imaging plate (IP) is used for the X-ray detector 3 so as to detect small angle scatter X-rays which diverge from the sample S, in a wide range. In the optical device for small angle scattering system of the present embodiment, the X-rays a radiated from the X-ray source 2 enter to the multilayer mirror 1. However, since the distance L1 from the X-ray source 2 to the multilayer mirror 1 is set short as described above, the X-ray intensity a hardly attenuate within this distance and high X-ray intensity may be kept. The X-rays a that entered from one end to the multilayer mirror 1 are alternately reflected between the first reflection part 1a and the second reflection part 1b and output to the other end. Then, the reflecting X-rays b output from the multilayer mirror 1 are converged at the convergent angle xcex8c. As the convergent angle xcex8c is adjusted to nearly twice that of the divergent angle xcex4 herein, almost parallel beam are formed by the X-rays c reflected at the divergent angle xcex4 around the reflected X-rays b as described above (see FIG. 3). Moreover, the convergent angle xcex8c set as above is a small angle as described above. Accordingly, the X-ray detector 3 may be arranged at a location apart from the convergent point B of X-rays (in other words, sample location), and high small angle resolution may be obtained. When the reflected X-rays b are irradiated to the sample S thereby, small angle scattering of X-ray are taken out from the sample S. The small angle scattering of X-ray are detected by the X-ray detector 3 (IP) at the downstream. Additionally, when a distance between the sample S and the X-ray detector 3 is widened, air scattering of X-rays increases and a background rises. Accordingly, S/N ratios in measurement may become worse. In order to solve this problem, it is preferable to cover a gap between the sample S and the X-ray detector 3 with a vacuum pass. Furthermore, for the same reason, it is desirable to cover each gap of the slits 4, 5, 6 therebetween with a vacuum pass.