高エネルギーアンジュレータビームラインにおけるタンパク結晶構造解析のための波長可変型二次元集光モノクロメータの開発

Protein crystal stmcture analysis is a powerful tool for revealing threedimensional stmctures of biological macromolecules at atomic resolution, In order to collect reflection data rapidly from sample crystals and to resolve phase problems resulting from anomalous dispersion effects, synchrotron radiation with high intensity and a wide range of accessible energies is very useful in protein crystallography. In second-generation synchrotron radiation facilities, however, X-ray energies applicable to protein crystallography have been limited to below 20 keV since the bending magnets in these facilities generate X-rays with a sufficiently high flux only at energies below 20 keV. In the third-generation facilities, such as the SPtmg-8, high-brilliance X-rays have become available in a wide energy range of 6-40 keV from an in-vacuum undulator having fundamental and third-harmonic emissions. High-intensity X-rays in the region between 20 and 40 keV, which are not available in the second-generation facilities, are desired in protein crystallography since errors caused by absorption of X-rays by a protein crystal are essentially eliminated. However, there exist no optical elements suitable for converging high-energy X-rays in horizontal and vertical directions. Total reflection mirrors cannot be used because the critical angles are so small that the radii of curvature are very large. The triangular bending monochromator must be combined with another focusing element such as a total reflection mirror in order to realize two-dimensional focusing. The sagittal focusing monochromator is, in general, used to obtain a pseudo-twodimensional focal point. However, its application to X-rays from an undulator is not feasible since the size of the X-rays is too small for convergence using the sagittal focusing geometry. There are also various types of two-dimensional focusing monochromators fabricated by simultaneous bending in two directions. None of these, however, are tunable in the X-ray energy range. Because tunability is an indispensable function of monochromators used in protein crystallography, these monochromators cannot accommodate the present purpose. It is clear that reliable two-dmensionally tunable focusing monochromators must be developed in order to effectively utilize high-energy and high-intensity X-rays, that are extracted from the undulator beamlines in the third-generation facilities. In this dissertation, a newly developed two-dimensionally tunable focusing monochromator will be described. It consists of a silicon wafer which has an oblique-cut angle between the Bragg net plane and the crystal surface and is adhered onto a tablelike copper block. The radii of curvature are varied independently in sagittal and meridional directions by expanding the spaces between the table legs. The versatilities of the meridional and sagittal curvatures were confirmed from the results of X-ray experiments and three-dimensional shape measurements, respectively. The two-dimensional focusing ability was demonstrated using high-energy X-rays of 3777 keV emitted from a bending magnet source of the Photon Factory. A quasi-isotropic profile of converged X-rays was achieved near the focal position. The apparent gain of photon flux was 21. Owing to these excellent characteristics of the monochromator, a diffraction pattern of hen egg white lysozyme crystal was successfully obtained using high-energy X-rays. If the present monochromator is used in the SPring-8 undulator beamline, the high-energy X-rays between 20 and 40 keV may have 105 times higher intensity than that of X-rays obtained from the Photon Factory bending magnet beamline. In addition, heavy elements from cadmium to iodine are applicable to phase determination. This monochromator will contribute much to the elucidation of the structures of biological macromolecules in the near fuure.