Application of synchrotron radiation to anomalous scattering for structure analysis with a four-circle diffractometer

A newly built four-circle diffractometer for X-ray structure analysis with synchrotron radiation and particularly with the use of anomalous scattering due to a relatively heavy atom or atoms is described. This system is installed on beam-line 10A in the Photon Factory (PF) in the National Laboratory for High Energy Physics, and its 2theta arm is rotated in the plane perpendicular to the floor. In this system, a one-crystal monochromator of the horizontal dispersion type is used. When the 111 reflexion from a Si monochromator is used, the energy resolution is about 14 eV for X-rays of about 10 keV. The four-circle diffractometer, a monochromator and an alignment carriage for the four-circle diffractometer can be controlled by a computer and, therefore, once the optical system has been adjusted for X-rays of a certain wavelength then the diffraction intensity values from a single-crystal sample can be automatically measured at any wavelength chosen. An NaI(Tl) scintillation counter is used for both the intensity measurements of the diffraction beam and the monitoring of the incident-beam intensity. With this diffractometer, diffraction intensities have been measured for a hemimorphite single crystal at two energy values on both sides of the Zn K absorption edge. (Auth.)