1,190,555. X-ray spectrometer with blazed diffraction grating. CAMBRIDGE INSTRUMENT CO. Ltd. 13 Feb., 1968 [16 Feb., 1967], No. 7461/67. Heading H5R. [Also in Division G2] An X-ray spectrometer comprises an X-ray source S, a curved blazed diffraction grating P, and a detector D all being maintained on a Rowland circle of radius R, the grating P being movable on a path, which may be rectilinear, towards and away from the source S, the detector D being moved on a linkage or gearing so that it has twice the angular velocity around the circle, with respect to the source, of the grating, the grating being mounted on a support which has an additional point PSP1/SP also lying on the Rowland circle and spaced from the mid point P of the grating so that the distance P-PSP1/SP subtends at the centre of the Rowland circle an angle of twice the blaze angle of the grating, means being provided to keep the additional point PSP1/SP equidistant from the source S and detector D, the linkage or gearing that acts on the detector comprising an arm connected to the detector and pivoted on a point lying on the Rowland circle. The arm may be pivoted at the additional point PSP1/SP or it may also be pivoted at the mean point P of the grating. The means to keep the additional point equidistant from the source S and detector D may comprise a cord or tape E of thin flexible but inextensible material, e.g. metal strip, extending from the detector around the additional point PSP1/SP to a clamping point F on an extension of the straight line joining S to PSP1/SP, the clamping point being a fixed distance from the source. In the preferred embodiment the mean point P and the additional point PSP1/SP both follow rectilinear paths which (if extended) pass through the X- ray source which is fixed in space, the clamping point F being similarly fixed. The cord or tape E may be kept taut by a tension spring H or its equivalent. The X-ray source S may be a point source generated on a sample by a focused electron beam or it may be a beam collimated from a diffuse source of X-rays. The spectrometer mechanism may be mounted in a vacuum chamber, the centre of the Rowland circle lying outside the chamber in some or all of the operative positions of the spectrometer.
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