Improved apparatus for plotting x-ray diffraction pole figures

摘要

916,720. Automatic plotting of X-ray diffraction patterns. UNION CARBIDE CORPORATION. July 14, 1961 [July 18, 1960], No. 25495/61. Class 40 (3). [Also in Group XIX] The invention relates to apparatus, Fig. 1, for automatically plotting X-ray diffraction pole figures in which a specimen is irradiated by a collimated X-ray source and a Geiger-Mueller tube is employed to detect and measure the intensities of the refracted rays, a scan over a hemisphere being effected in a spiral path by rotating the specimen about both horizontal and vertical axes. In accordance with the invention, the output of the detector is applied through an amplifier to a recorder generating a spiral trace in synchronism with the scanning pattern (i.e., as shown in Fig. 3, the angular rotation of the recorder is synchronized with the angular rotation # of the specimen about the vertical axis whilst the radial displacement from the outside of the record is synchronized with the angular rotation α about the horizontal axis), means being provided for producing an increased trace area per unit area of the recorder sheet as the signal from the detector increases in magnitude. The effect is to produce a record in which not only the diffracted ray angles but also their magnitudes may be readily seen. In a first arrangement, the detector output is applied to a device which produces an output signal of a frequency proportional to the amplitude of the input signal. This signal of varying frequency is then applied to the recorder in such manner as to vary the radial displacement and results in a record as shown in Fig. 2 where the apparent line density increases with X-ray intensity. In a second arrangement, the detector signal is quantized to a predetermined number of amplitude levels, e.g. four, and a pulse-type output signal is generated in which the mark-space ratio depends upon the signal amplitude. This pulse signal is then applied to control the recording, either directly where electro-sensitive paper is employed, or indirectly by operation of the pen-lift relay when pen recording is employed. This resulting record takes the form shown in Fig. 3 where for the first and lowest level of signals no record is made, for the second level there are short dashes, for the third level there are longer dashes and for the fourth and maximum level there is a continuous trace. A pulse signal of this character may be produced by an arrangement as shown in Fig. 4 where a potentiometer 12 is employed, the setting of the tappings of which (controlled by rotation of shaft 10) is retroactively controlled so as to balance the detector output. The shaft rotation is then employed by means of switch 14, 16, 18, 20 to select one of four switches 26 which are actuated by motor-driven cams 24 to produce different mark/space ratios. Where pen recording is employed the switch circuit is completed through the pen lift relay 28. Reference is made to the use in the invention of both a polar recorder and an X-Y recorder operated with a spiral time-base generator. Such a generator may conveniently comprise a conventional potentiometer whose shaft is positioned in accordance with angle α, Fig. 1, and whose output is fed to a sine-cosine potentiometer whose shaft is positioned in accordance with angle #. Where it is desired to produce a record of the type shown in Fig. 2 the variablefrequency signal is impressed across a resistor in the connection between the two potentiometers. Reference is made to records having both constant and non-constant spiral pitches. U.S.A. Specifications 2,798,957 and 3,008,791 are referred to.