GB677981A - Improvements in or relating to magnetic induction accelrators for producing x-rays - Google Patents

Abstract

677,981. Magnetic induction accelerators; X-ray tubes. ILLINOIS, BOARD OF TRUSTEES OF THE UNIVERSITY OF. May 30, 1945 [May 4, 1944], No. 13624/45. Class 39 (i). A magnetic induction accelerator for producing X-rays which is operated so that a beam of positively or negatively charged particles travels in a generally ring-shaped orbit and is displaced either radially or axially on to a target and also has an oscillatory motion in a direction at right angles to such radial or axial displacement, has a target whose width, measured in the direction of the oscillatory motion of the beam particles, is appreciably less than the amplitude of the oscillatory motion. The dimension of the target in the axial direction of the orbit may be less than 1 mm. or not greater than 0.01 inches and the surface of the target presented to the beam is convex. The accelerator comprises a magnetic frame 12, Fig. 1, having upper and lower polepieces 13 and 14, Fig. 4, disposed centrally of the rectangular yoke 15. The polepieces 13 and 14 are formed of sectorshaped laminated components, and the yoke 15 is also laminated. A pair of spaced laminated discs 16 controls the flux density through the central part of the polepieces to maintain the equilibrium orbit of particles in the evacuated electron tube 17. The walls of the tube 17 and the base of the laterally extending neck 20, Fig. 6, is made of a unitary piece of porcelain, a glass extension 21 being sealed to the neck 20. The inside of the tube is preferably silvered to produce a high resistance conductive coating which is connected to earth. Circular exciting coils 18, 19 surround the polepieces 13 and 14. The electron gun 22 comprises a tungsten filament 23 supported upon terminal leads 24, 25 which pass through the pinched glass seal 26 formed on the inner end of the inner tube 27 which has flanges 2.8 sealed at 29 to the glass extension 21. A channel-shaped molybdenum grid focuses the electrons from the filament 23 through the slot or opening 30 in the front wall of the rectangular box-shaped molybdenum plate 33 supported upon the molybdenum lead 37 fixed in a portion 38 of the glass tube and electrically connected to a lead 39 extending through the tube 27 at 40. The focusing grid 32 is supported upon an electrode lead 42. The target 45 is attached to the outer wall of the plate 33 and consists of a minute solid body of a heavy metal such as tungsten, platinum, gold, thorium or uranium and is preferably connected to earth. The target 45 is shaped as shown or may consist of a semi cylindrical piece of metal with the convex side tangential to the orbit of the beam. The target may be disposed so that the beam is spiralled radially outwardly or radially inwardly on to it. As shown in Fig. 11, the beam 46<SP>1</SP> may be spiralled inwardly on to a target 45<SP>1</SP>. By adjustment of the magnetic field the beam may be depressed below the median plane x<SP>1</SP>-x of the beam, i.e. axially spiralled, and may then be spiralled outwardly to bring the electrons into engagement with the target 45<SP>11</SP>. Fig. 14 shows a pair of electron guns 22<SP>1</SP>, 22<SP>1</SP>, the beam 46<SP>1</SP> being spiralled outwardly to impact the target 43 supported independently between the electron guns.