Patent Number: 
Section: claims

1. An X-ray optical system comprising:an X-ray source, which generates an X-ray beam having a linear section;a diverging-beam path, in which the X-ray beam diverges with a predetermined divergence angle in a plane including both a direction perpendicular to a longitudinal direction of a cross section of the X-ray beam and a traveling direction of the X-ray beam, the plane being referred to as a specific plane hereinafter;a parallel-beam path, in which the X-ray beam travels in parallel in the specific plane;a parabolic multilayer mirror, which is arranged between the X-ray source and the parallel-beam path, and has a reflective surface having a parabolic shape in the specific plane and a parabolic focal point located on the X-ray source, and reflects the X-ray beam coming from the X-ray source at the reflective surface to generate a parallel beam;an optical-path selection slit device, which allows any one of the diverging and parallel beams to pass through and interrupts other of the diverging and parallel beams; anda polycapillary optics, which is detachably inserted into the parallel-beam path at a position behind the optical-path selection slit device, and receives the parallel beam and discharges a converging beam focused on a point. 2. The X-ray optical system according to claim 1, wherein the polycapillary optics has one end for receiving the parallel beam, the one end being elongate in cross section so as to receive the parallel beam having a linear section. 3. The X-ray optical system according to claim 1, wherein the polycapillary optics is arranged so as to be exchangeable for a Soller slit, which restricts a vertical divergence of the X-ray beam having the linear section. 4. The X-ray optical system according to claim 1, further comprising an exit-width restriction slit arranged on an X-ray discharge side of the polycapillary optics. 5. The X-ray optical system according to claim 4, wherein the exit-width restriction slit is formed with a circular aperture. 6. The X-ray optical system according to claim 1, wherein the polycapillary optics is of a monolithic type, which has a honeycomb structure in a cross section perpendicular to an axial direction of the polycapillary optics. 7. The X-ray optical system according to claim 1, wherein the polycapillary optics is adjustable by rotation for an angular alignment between the parallel beam and the polycapillary optics.