GB536449A - Improvements in or relating to secondary ray diaphragms for ray investigation - Google Patents

Abstract

536,449. R÷ntgen-ray apparatus. ITEN, J. Nov. 9, 1939, No. 29765. [Class 98 (i)] A secondary ray diaphragm for use in X-ray photography comprises a screen adapted to be moved between the source of rays and the sensitive surface and formed of a number of narrow sections, each formed of a number of laminae, the planes of the laminae being always directed towards the ray source. The apparatus shown comprises a casing 10 having a slot (not shown) at one end for the insertion of the film cassette, which is supported on a plate 12, and containing a secondary ray screen in the form of an endless belt composed of narrow laminated screen sections 24 mounted at their ends by pins 22 on a pair of chains 20. carried by sprockets 19 on hollow shafts 14, 14<SP>1</SP> which are rotated by a motor. At one end each screen section 24 carries a plate 25 on which a pin 26 co-operates with a spring 27 to tend to hold the section with the laminations vertical. The lower and upper ends of these plates contact respectively with inclined guide rails 29, 30, each extending over half the length of the screen the effect being to incline the segments in reverse directions on each side of the centre of the screen and with increasing inclination towards the ends so that the planes of the laminae are always directed towards the source of the rays. The rails 29, 30 are pivoted at 31 and may be simultaneously adjusted as regards their inclination by screws 33 operated by an external control, in order to adjust the apparatus for different distances between the source of rays and the film. In other forms the sections are secured to a fabric or rubber band which is guided over rollers or carried by a link chain or a metal band or cable, the screen elements having at their ends bosses which bear on curved guide rails by which the inclination of the elements is controlled. Forms in which the upper run of the screen is curved, intended especially for the examination of welded seams of tanks and boilers are illustrated. The screen elements may also be mounted in a reciprocated frame. Fig. 16 shows a section of a screen element consisting of alternate ray-permeable strips 45 and lead strips 44 enclosed in a tube 48 of paper or light metal and having at the bottom a strip of tin 46 to filter out radiation from the lead, and a strip of copper 47 those from the tin, radiation from the last being removed by the aluminium casing of the cassette. Alternatively, the tin-copper-aluminium filter may form the top and bottom of the cassette or be applied to it. The lead strips 44 may be replaced by tin, in which case the filter is unnecessary, but thicker strips must be employed, which weaken the primary rays. The tin strips may therefore be of stepped or wedge section with the thicker edge at the bottom. In order that the distance between the object and the film may be as small as possible the edges of the strips may be rounded, the outer two laminae at side of the section being of less height than the remainder. A modified form of section comprises an upper and lower layer of laminae the laminae in the one layer extending transversely to those in the other.