A new diffraction method has been developed in which the intensity of Bragg re¯ections is measured while changing continually the wavelength of the radiation over a range in the vicinity of the absorption edge of an atom contained in the crystal. It is shown that the intensity gradient with respect to the wavelength of the hkl re¯ection is in a simple relation to the real and imaginary parts of the structure factor of that re¯ection and, if the positions of the anomalously scattering atoms are known or properly assumed, the phase of F(hkl) can be derived by solving simultaneous linear equations. The procedure is particularly simple when the crystal is centrosymmetric. The method, called the wavelengthmodulated diffraction (WMD) method, is free from the problem of intensity scaling encountered in other methods of phase determination. Synchrotron radiation is most suited to WMD measurements. Suggestions on how to measure the intensity gradient are given and the possible errors involved are discussed.

A compact superconducting storage ring installed at Ritsumeikan University is operated at an electron-beam energy of 0.575 GeV and an initial beam current of 300 mA. The radius of the circular electron orbit is as small as 0.5 m, suggesting that the radiation emitted contains short-wavelength components. With an imaging plate as a detector, X-ray precession diffraction patterns were recorded for organic single crystals within a reasonable period of time using radiation of wavelength 0.155 nm (8 keV) to 0.248 nm (5 keV). The use of the radiation in the structural study of organic crystals containing 3d metal atoms using the phenomena of anomalous scattering is described. If appropriately planned, Xray diffraction and/or scattering experiments can be made at the compact ring without recourse to a large-scale ring.

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A new diffraction method has been proposed in which Bragg reflections are recorded with changing continually the wavelength of synchrotron radiation in the vicinity of the absorption edge of an atom contained in a crystal. It is shown that the intensity gradient with the wavelength of the h k l reflection is in a simple relation to the real and imaginary parts of the structure factor of that re-flection and, if the positions of the anomalously scattering atoms are known or properly assumed, the phase of F(h k l) can be derived by solving two simultaneous linear equations. The procedure is particularly simple when the crystal is centrosymmetric. The method, called the wavelength-modulated diffraction method, is free from the problem of intensity scaling encountered in other methods of phase determination.