Patent GB-1426102-A (GB)
Title: Apparatus for x-ray crystallography
IPC: G01N23/20
Filed: 1973-01-29
Abstract: 1426102 X-ray crystallography SOC NATIONALE DES PETROLES D'AQUITAINE 29 Jan 1973 4403/73 Heading G1A X-ray crystallography of samples containing crystalline and amorphous elements is performed using apparatus comprising an X-ray source, a sample holder, an instrument for measuring the intensity ID of the diffracted radiation, an instrument for measuring the intensity I C  of the Compton scattered radiation, means for calculating the content of the crystalline component represented by the ratio I D /I C  and means for determining the ratio of the area between the scatter halo curve and the abscissa axis to the surface are between the diffraction peaks and the same abscissa axis to represent the mass ratio of the amorphous and crystalline elements. As shown, Fig. 3, an X-ray tube 1 illuminates a sample 3 mounted on a rotatable holder 4 the diffracted radiation being detected by an instrument 6 mounted on a goniometer arm which rotates at twice the speed of the sample holder 4. The instrument 6 comprises a monochrometer utilizing a curved diffracting crystal 9 and a detector 10. The angle of the detector and crystal are adjusted to select radiation of a wavelength corresponding to the element of interest. The Compton scattered radiation is received by a second identical instrument 11 positioned adjacent to the tube 1 and adjusted to select radiation of a Compton scattered wavelength corresponding to the incident wavelength of the element. The apparatus is operated by starting at a small diffraction angle and counting the number of pulses over a short interval of time determined by a quartz clock. The contents of counter 17 are transferred to a store 18 and thence to a recording medium 19 which may be a graph recorder, a punched card or magnetic tape. A sequence of measurements are taken at intervals determined by a clock fed from the goniometer power supply to ensure that the measuremerits are made at accurately known positions of the goniometer arm and hence diffraction angle. When the goniometer arm reaches the position of maximum diffraction angle the Compton scattering measurement is made. The recorded data are processed to calculate the concentration of the selected element and also to draw a graph of I D /I C  versus the diffraction angle from which the mass ratio of crystalline to amorphous material can be determined. If the sample is small it may be supported on a thin film of a material having a low scatter coefficient, e.g. polypropylene. Control  circuitry is provided to change the sensitivity of the counting circuitry and to increase the time constant during the Compton measurements and the exit slit 2 of the X-ray tube is also opened. The scattered radiation measurement may be limited to the area of the target by means of a diaphragm having an aperture of suitable size and shape. In a modification, Fig. 4 (not shown), the waveband selection for the Compton scattering measuring instrument 11 comprises a double Ross filter. Measurements are made sequentially through two filters of materials having spaced absorption edges and the resulting counts subtracted to give the intensity of the radiation at wavelengths between the absorption edges of the filters. The filters may be arranged in a slide moved by means of a solenoid, or in a rotatable wheel. The scatting measurement is made at a small diffraction angle (7¢ degrees to 17¢ degrees) without increasing the size of the source slit 2.