SEPARATION OF OBSERVED INTEGRATED INTENSITIES INTO COHERENT AND INCOHERENT COMPONENTS. T. Takama, T. Nishide and *A. Onodera, Department of Applied Physics, Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060, Japan and *Department of Physics, Faculty of Science, Hokkaido University, Kita-ku, Sapporo 060, Japan.

The statistical dynamical theory of diffraction by Kato (Acta Cryst. A36, 1980, 763-778) has great potential to predict diffraction from perfect to imperfect crystals. The theory has been improved theoretically and tested experimentally. It is, however, far from satisfactory for practical applications to extinction correction and still in the development stage. The integrated intensity in the theory consists of the coherent and the incoherent terms (including the mixed term). The terms are related to crystal perfection, wavelength, crystal thickness and reflection plane. Therefore, one of the ways to advance the theory is to clarify the relations experimentally.

In the present study, the integrated intensities from Si single crystals with different perfection were measured and separated into the two terms. Dislocation-free Cz-Si single crystals with a thickness of about 0.5 mm were used for the experiment. Micro defects of SiO₂ with random distribution were introduced into the specimens by annealing at 1073 K for 4 h then at 1273 K for 1 to 32 hr in dry oxygen gas. The oxidized surface layers were removed by chemical etching. The integrated intensities on the symmetrical Laue case were measured by two separate methods using white X-rays as an incident beam. In one method, the intensities were measured as a function of wavelength and in the other for fixed wavelength as a function of crystal thickness. It was observed that both the intensities and the Pendellösung beats spacing increase and the amplitude of beats decreases depending on the annealing time and the reflection index. The coherent parts were separated from the intensities using the amplitude of the beats as a clue. The incoherent parts were obtained by subtracting the intensities due to the Borrmann absorption from the remainders. The two parts were compared with the model in which the correlation length of amplitude in the theory is assumed to be a free parameter (Takama and Harima, Acta Cryst. A50, 1994, 239-246). The result showed a fairy good agreement between the model and the present experiment.