Patent Number: 
Section: claims

1. A method for X-ray wavelength measurement carried out by using a first channel-cut crystal for wavelength measurement in which two opposing cut planes are formed and the lattice constant of which is known, said method comprising the steps of:rotating, by utilizing a turntable, said first channel-cut crystal with respect to an incident X-ray beam direction in respective arrangements of (−, +) and (+, −) with said first channel-cut crystal, wherein (+) or (−) is defined as a crystal arrangement which causes a same or opposite X-ray bending direction to a first X-ray bending direction of diffraction; anddetermining an absolute wavelength of X-ray from a difference between crystal rotation angles in said respective arrangements. 2. The method for X-ray wavelength measurement according to claim 1, further comprising the steps of: collimating X-rays to be parallel light by a collimator arranged on an X-ray incident side of said first channel-cut crystal and then guiding the parallel light into said first channel-cut crystal to carry out wavelength measurement. 3. The method for X-ray wavelength measurement according to claim 1, wherein a second channel-cut crystal is placed for collimator which is arranged on an X-ray incident side of said first channel-cut crystal and in which two opposing cut planes are formed, said method further comprising the steps of:diffracting X-ray at a crystal plane having the same index as that of a crystal plane at which said first channel-cut crystal diffracts X-ray at respective cut planes of said second channel-cut crystal; andguiding the diffracted X-ray into said first channel-cut crystal to carry out wavelength measurement. 4. An X-ray wavelength measurement apparatus, comprising:a first channel-cut crystal for wavelength measurement in which two opposing cut planes are so formed that at least a part of mutual projections thereof overlap with the cut planes; a detector for detecting the intensity of X-ray spectrally reflected by said first channel-cut crystal; andturntable for rotating said first channel-cut crystal with respect to an incident X-ray beam direction such that a rotation center of said first channel-cut crystal is set to be capable of diffracting X-ray in respective arrangements of (−, +) and (+, −), wherein (+) or (−) is defined as a crystal arrangement which causes a same or opposite X-ray bending direction to a first X-ray bending direction of diffraction. 5. The X-ray wavelength measurement apparatus according to claim 4, further comprising a collimator arranged on an X-ray incident side of said first channel-cut crystal, wherein X-rays are collimated to be parallel light by said collimator and then guided into said first channel-cut crystal carry out wavelength measurement. 6. The X-ray wavelength measurement apparatus according to claim 4 wherein:the rotation center of said first channel-cut crystal is set between said two opposing cut planes of said first channel-cut crystal or between extended planes of said two opposing cut planes; anda cut plane on which X-ray is incident when said first channel-cut crystal diffracts the X-ray in the arrangement of (−, +) differs from that on which X-ray is incident when said first channel-cut crystal diffracts the X-ray in the arrangement of (+, −). 7. The X-ray wavelength measurement apparatus according to claim 4 wherein:the rotation center of said first channel-cut crystal is set in a position that allows X-ray to enter an identical plane of the opposing cut planes when said first channel-cut crystal diffracts X-ray in each of arrangements of (−, +) and (+, −). 8. The X-ray wavelength measurement apparatus according to claim 7, further comprising a rotation control mechanism for controlling the rotation of said first channel-cut crystal, whereinsaid rotation control mechanism includes an angle detector having self-calibration function for detecting displacement of a scale position of a rotation angle. 9. The X-ray wavelength measurement apparatus according to claim 4 inclusive, further comprising a rotation control mechanism for controlling the rotation of said first channel-cut crystal, whereinsaid rotation control mechanism includes an angle detector having self-calibration function for detecting displacement of a scale position of a rotation angle. 10. An X-ray wavelength measurement apparatus, comprising:a first channel-cut crystal for wavelength measurement in which two opposing cut planes are so formed that at least a part of mutual projections thereof overlap with the cut planes;a second channel-cut crystal for collimator which is arranged on the incident side of said first channel-cut crystal and in which two opposing cut planes are formed;a detector for detecting the intensity of X-ray spectrally reflected by said first channel-cut crystal; anda turntable for rotating said first channel-cut crystal with respect to said second channel-cut crystal such that a rotation center of said first channel-cut crystal is set to be capable of diffracting X-ray in respective arrangements of (−, +) and (+, −), wherein (+) or (−) is defined as a crystal arrangement which causes a same or opposite X-ray bending direction to a first X-ray bending direction of diffraction; andsaid second channel-cut crystal diffracts X-ray at a crystal plane having the same index as that of a crystal plane at which said first channel-cut crystal diffracts X-ray, to guide the diffracted X-ray into said first channel-cut crystal. 11. The X-ray wavelength measurement apparatus according to claim 10, wherein said second channel-cut crystal is placed for fixing the rotation for incident X-ray upon carrying out wavelength measurement. 12. The X-ray wavelength measurement apparatus according to claim 11 wherein:the rotation center of said first channel-cut crystal is set between said two opposing cut planes of said first channel-cut crystal or between extended planes of said two opposing cut planes of said first channel-cut crystal; anda cut plane on which X-ray is incident when said first channel-cut crystal diffracts the X-ray in the arrangement of (−, +) differs from that on which X-ray is incident when said first channel-cut crystal diffracts the X-ray in the arrangement of (+, −). 13. The X-ray wavelength measurement apparatus according to claim 11 wherein:the rotation center of said first channel-cut crystal is set in a position that allows X-ray to enter an identical plane of the opposing cut planes of said first channel-cut crystal when said first channel-cut crystal diffracts X-ray in each of arrangements of (−,+) and (+,−). 14. The X-ray wavelength measurement apparatus according to claim 10 wherein:the rotation center of said first channel-cut crystal is set between said two opposing cut planes of said first channel-cut crystal or between extended planes of said two opposing cut planes of said first channel-cut crystal; anda cut plane on which X-ray is incident when said first channel-cut crystal diffracts the X-ray in the arrangement of (−, +) differs from that on which X-ray is incident when said first channel-cut crystal diffracts the X-ray in the arrangement of (+, −). 15. The X-ray wavelength measurement apparatus according to claim 10 wherein:the rotation center of said first channel-cut crystal is set in a position that allows X-ray to enter an identical plane of the opposing cut planes when said first channel-cut crystal diffracts X-ray in each of arrangements of (−,+) and (+,−). 16. The X-ray wavelength measurement apparatus according to claim 10, further comprising a rotation control mechanism for controlling the rotation of said first channel-cut crystal, wherein said rotation control mechanism includes an angle detector having self-calibration function for detecting displacement of a scale position of a rotation angle.