Patent Number: 
Section: claims

1. An X-ray optical device for small angle scattering system, comprising a multilayer mirror providing a divergent angle xcex4 of reflected X-rays, and an X-ray source to radiate X-rays, wherein the multilayer mirror has at least the following conditions (a) and (b): (a) reflection faces are formed elliptically to have two focal points A, B; and  (b) a distance from a center of the reflection faces to the focal point B is set to provide a convergent angle xcex8c of X-rays at the focal point B that is nearly twice as great as the divergent angle xcex4, when the X-ray source is arranged at the focal point A to irradiate X-rays to the reflection faces. 2. The optical device according to  claim 1 , wherein the reflection faces are formed of a first reflection part and a second reflection part that are orthogonal to each other and have a multilayer structure, and the multilayer mirror is configured to converge X-rays reflected at each reflection part on the focal point B. claim 1 3. The optical device according to  claim 2 , wherein the first reflection part and the second reflection part have a multilayer structure in which thin layers formed of a material having a large atomic number and thin layers formed of a material having a small atomic number are alternately laminated on a surface of a substrate. claim 2 4. The optical device according to  claim 1 , wherein a sample is arranged at the focal point B of the multilayer mirror. claim 1 5. The optical device according to  claim 4 , wherein a first slit and a second slit are arranged along an optical axis of X-rays reflected at the multilayer mirror to prevent the diverging X-rays, and a third slit is arranged near another focal point B of the multilayer mirror to shield parastic scattering from the multilayer mirror. claim 4 6. A multilayer mirror for small angle scattering, providing a divergent angle xcex4 of reflected X-rays and having at least the following conditions (a) and (b): (a) reflection faces are formed elliptically to have two focal points A, B; and  (b) a distance from a center of the reflection faces to the focal point B is set to provide a convergent angle xcex8c of X-rays at the focal point B that is nearly twice as great as the divergent angle xcex4, when X-rays are irradiated from the focal point A to the reflection faces. 7. The multilayer mirror according to  claim 6 , wherein the reflection faces are formed of a first reflection part and a second reflection part that are orthogonal to each other and have a multilayer structure, and the multilayer mirror is configured to converge X-rays reflected at each reflection part on the focal point B. claim 6 8. The multilayer mirror according to  claim 7 , wherein the first reflection part and the second reflection part have a multilayer structure in which thin layers formed of a material having a large atomic number and thin layers formed of a material having a small atomic number are alternately laminated on a surface of a substrate. claim 7