GB439728A - Orthoscopic diaphragms for roentgen ray working - Google Patents

Abstract

439,728. R÷ntgen - ray screens. SIEMENS - REINIGER - WERKE AKT.- GES., 31, Karlstrasse, Berlin. Jan. 25, 1935, Nos. 2517 and 2518. Convention dates, Feb. 5, 1934 and Dec. 28, 1934. [Class 98 (i)] An orthoscopic screen for intercepting secondary radiation comprises an assembly of minute solid or tubular rods or needles, as of prismatic, cylindrical, truncated pyramidal, or conical form, made of ray-impermeable material such as lead, distributed irregularly but approximately uniformly over the area of the screen, the lengths of the rods or needles being substantially normal to the screen and directed towards a common point or line at a finite or infinite distance from the screen. Such a screen may be formed by cutting a disc of wood across the grain and filling its vessels as with metal, an alloy, or a lead compound ; or by perforating a plate with minute holes and filling them as with lead ; or by strewing pre-formed needles on a plate as of metal coated with a binding medium as of gelatin, erecting the needles by an electric field, warming the binder, cooling it again to fix the needles in erected position, and filling the interspaces with a ray-permeable liquid which sets ; or by pressing molten metal or alloy, or a paste containing lead, through the holes of perforated plate, hardening the extruded needles, and applying a filler; or by electrodeposition of needles on a metal plate and applying a filler ; or by forming by extrusion one or more fine wires as of lead coated with a binder as of gelatin, cutting into short lengths, assembling these in parallel juxtaposition and uniting them by heat, pressure, or application of a binder. Screens may also be formed by embedding needles e, Figs. 2 and 3, made for example of tungsten powder in a cellulose ester binder, transversely and irregularly in a carrier strip a as of unsized calendered paper, which may be coiled or doubled upon itself. The middle portion b of the coiled diaphragm may be a small disc cut eccentrically from another similar coil. Each face of the finished screen may be coated with waterproof varnish. The above methods produce screens with parallel elements, but curved screens may also be formed, as by bending in a steam bath a wooden screen produced as above. If such a screen is bent into the form of a spherical cap a, as shown in Fig. 1, screens of disc or other form may be produced from it by parallel cuts, as at f. The needles b are directed by the bending operation towards the position c of the ray-source. Reference is made to the movement of the screen during the radiographic exposure.