GB1067753A - Improvements relating to beam defining structures - Google Patents

Abstract

1,067,753. Beam - defining mechanisms. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Feb. 4, 1964 [March 19, 1963], No. 10873/63. Heading H5R. Apparatus for defining a beam of, e.g., X-rays from a point source 26 (Fig. 4), comprises one or more pairs of shutters 1, 2 whose surfaces 31, 32 are arranged always to extend radially from the point 26, each shutter being connected to the fixed frame 3 by a pair of link members 4, 5 or 6, 7 pivotally attached to both the frame and the respective shutter. The full absorption thickness of the shutters 1, 2 is thereby utilized at different positions of adjustment and a beam with sharp edges obtained. The mechanism described is equivalent to but more compact than a beam defining arrangement in which shutters are carried on arms N (Fig. 2, not shown), which are radially located with respect to the radiation source, but only provided that the shutter movement is small and that the angles through which each of the inner links 5, 7 moves, about its pivot to the fixed frame 3, is small. The outer links 4 and 6 have corresponding link members on the other side of the shutter to which they are joined by cross-members 41, 42. To move the shutters 1, 2 apart or together, rotation of the shaft 17 by a motor of by hand is transmitted by a universal joint 16 to shaft 15 carrying a worm 14 engaging a quadrant attached to the link 5. The links 5 and 7 are interconnected by quadrants 8 and 9. A pinion 11 is driven by the quadrant 9 to operate a pointer. The pivots of the linkages may be adjusted to set the inclinations of the surfaces 31, 32 initially. Shutter pairs may be arranged so that, e.g., rectangular or hexagonal beam cross-sections are obtained. The beam defining mechanism is mounted on a container 25 for the source with a surrounding mass of radiation absorbent material 28. The shutters may be of lead encased in steel.