GB865033A - Improvements in or relating to spectrometers - Google Patents

Abstract

865,033. Spectrometers. ONTARIO RESEARCH FOUNDATION. March 24, 1959, No. 10149/59. Classes 97(1) and 98(1) A spectrometer comprises a fixed source of radiation, a detector, and a plurality of diffraction elements on the Rowland circle including said source and detector; means are provided for selecting only that portion of the radiation beam from the source which falls on a particular diffraction element, and means are also provided for changing the positions of the detector and. the diffraction element with respect to each other and the source, while remaining on the Rowland circle passing through the source. The diffraction elements may include crystals having different lattice spacings, and also an optical grating, so that between them they can cover a spectrum band ranging from 0,01 to 150,000 Angstroms, i.e. X-rays, ultra-violet, visible, and infra-red. The principle of the invention is shown diagrammatically in Fig. 1. Radiation from the source S enters the spectrometer through aperture S<SP>*</SP>, spreading into a cone of angle 2w. The diffraction crystal K 1 and detector D 1 lie on the Rowland circle (centre M and radius R R ) passing through S<SP>*</SP>. The surface of the crystal is ground to coincide with the Rowland circle, and the lattice plane passing through K 1 has a radius of curvature of 2R R (i.e. centred at K<SP>1</SP>). This position corresponds to a reflected wavelength of A second position of the crystal and detector, corresponding to a wavelength of # 2 , is shown at K II and D II respectively. These still remain on the Rowland circle passing through S*, so that the whole Rowland circle has in effect been swung about S*. Fig. 2 shows how selection of a particular part of the beam of radiation is made, by means of a movable slotted plate B1, which allows only a part of the beam to pass. Thus any particular spectral range is selected by shifting plate B1 to allow radiation to fall on one of the crystals K, or the grating. A practical form of the apparatus is shown in Figs. 4 and 8, which for simplicity has one crystal only (11). The detector is a chamber 14 having a slit plate 15 at its entrance, the slit lying along an axis y<SP>1</SP>. The chamber can swing on pivots C at the ends of arms 16; the other ends of arms 16 swing on a pivot 8 which is the centre of a cam follower 12. This rides on a fixed cam 13 so that pivot 8 always moves in a circle of radius R R centred at S*. Thus when pivot 8 is stationary, detector 14 (which is carried by rails 18 pivoted at B) moves along the Rowland circle shown (Fig. 4). When pivot 8 rolls along cam 13, this is the equivalent of swinging the whole Rowland circle about S<SP>*</SP>, as described with reference to Fig. 1. All the diffraction elements are mounted at one end of sectors 7 attached to pivot 8; this end is secured to a slide 4 mounted on a leadscrew 3 which can be turned by a wheel 5, thus causing the slide to move up and down the leadscrew as required, so altering the position of the crystal 11. To maintain the relation BS<SP>*</SP>= BC, a cord attached to an axle F passes round rollers j, k fixed to parts 4, 7 respectively. Since vacuum conditions are required for certain parts of the spectrum range covered by the apparatus, it is enclosed in an evacuated chamber 1. This is connected to the atmosphere at S by a pressure stage stretch 2.