Patent GB-816772-A (GB)
Title: Method and apparatus for electromagnetically separating isotopes
IPC: B01D59/48
Filed: 1945-10-22
Abstract: 816,772. Mass separators. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Oct. 22, 1945 [Oct. 9, 1944], No. 27833/45. Class 39(1). In a method of electromagnetically separating isotopes, e.g. U238 and U235, on a large scale, the space charge of the beam is neutralised by providing in and adjacent the beam sufficient quantities of charged particles of opposite electrical sign. The ion beam has a current value of at least 100 milli-amperes and the gas pressure is preferably in the range 10-3 to 10-5 mm. Hg. The atmosphere may be air. The charged particles for neutralizing the space charge may be produced by ionization of the gas in the path of the beam or by collisions of ions with the chamber walls. The isotopes are producing by ionising a gas or vapour, e.g. uranium tetrachloride, in an arc discharge and then accelerating the ions to an energy at least 4,000 times that of their initial thermal energies. An electrically conducting liner may be provided within the vacuum tank and the vacuum tank may be at the potential of the ion collectors or at the potential of the ion source. The instrument is termed a "calutron" and two constructions are described in detail. One construction utilizes a 37-inch cyclotron magnet and the other an 184-inch cyclotron magnet. General arrangement of " 37-inch " calutron, Figs. 3, 5, 17 and 19.-The vacuum tank 121, Fig. 3, is mounted on tracks 128, 129 so that it can be easily moved. Within the tank are an ion source block 299, a pair of accelerator plates 357, 359, pairs of beam defining and focusing plates 387, 388 and an ion collector 410. Ion source.-The ion source block 299, Fig. 5, has a charge cavity 302. a vapour exit slot 326, and a cavity 306, containing a heater 307. The slot 326 is enlarged at 346 to form an arc chamber. Electrons are projected into the arc chamber from a filament 328. The filament leads 337, 338 are water cooled. Adjustments of ion source block.-The ion source block 299, Fig. 3, is mounted at the end of an adjustable stem 295 which is carried, at the end of a tubular insulator 206, in a framework consisting of a bellows 263 and a pair of arms 228 pivoted on studs 226. The framework is biased angularly counter clockwise by a spring within a sleeve 289 to bear against a rod 281, and the adjustment is controlled by a screw shaft 271. Axial movement is controlled by a gear which engages a threaded sleeve at the end of the bellows 263. Adjustments of accelerator plates and beam defining plates.-One of the accelerator plates, 359 can be rotated slightly to vary its spacing from the other accelerator plate 357, by means of a lever-plate 368, pivoted at 368, and a crank shaft 379. The beam defining plates 387, 388 are mounted on wheels which run on tracks 393, 396. The plates 387, 388 can be moved by means of axially movable rods 399. Ion collector.-An ion collector 410, primarily for testing, consists of a cylindrical shell 411, Fig. 17, which is provided with differently sized slots 412, 432, one or other of which can be placed in the path of the ion beam by rotation of the shell through 180 degrees. The ions are collected on plate 413. In an alternative collector, Fig. 19, slot 488 and plate 488 are for testing a restricted portion of the ion beam, while slots 496, 497 and pockets 498, 501 are for collecting and retaining material. Modification utilizing a "cold" or grounded ion source.-In a modification utilizing a " cold " or grounded ion source, Figs 22 and 23 (neither Fig. shown), the ions travel through a C-shaped tank liner which is at the same potential as the accelerator electrodes and the ion collector. General arrangement of "184-inch" calutron, Figs, 26 &c.-A C-shaped tank 711 Fig, 26, contains an ion source unit 751, an accelerator mechanism 1461, a collector unit 723 enclosed in a houisng 722, and a liner 1666 which encompasses a transition liner 1676 at its ion source end. Observation windows 742 are provided in the tank. Ion source.-The ion source unit 751 consists of a block 812, Fig. 30, made up of a furnace block 853 containing a charge chamber 858 and heaters 868, a plate 851 containing a vapour distribution chamber 902 and a heater 911, and a plate 813 containing an arc chamber 921. Pipes 881, 886 are also provided for circulating cooling or heating fluid. A quartz baffle 926 is provided within the arc chamber 921. Ions generated in the arc chamber leave the chamber through an exit slit 1309. The slit 1309 is defined by a pair of plates 1307, 1308, and by a further pair of plates 1311, 1312 which are adjustable on the plates 1307, 1308. Supplementary beam defining plates 1401, 1402 are provided in advance of the slit 1309. The accelerator mechanism 1461 comprises a pair of plates 1462, 1463. An electron stream for generating the ions within the arc chamber is derived from a filament 931, Fig. 29, and enters the chamber through a confining aperture. The electron stream is received on an anode plate 1301 secured to the bottom of the plate 813, Adjustments of the ion source block.-The ion source block 812, Fig. 29, can be moved about an axis 757 from outside the face plate 712 of the vaccum tank. The block is supported by screws 806 on a pair of arms 802, the arms 802 being fixed to a plate 756. The plate 756 is constrained against all motion except a limited rotation about the axis 757. The plate 756 is moved by a pin 761 which slides in a block 758 attached to the plate. The pin 761 is translated sideways along a screw shaft 766. The screw shaft 766 is turned by means of a worm wheel mechanism 776. A vacuum-tight seal around the shaft 782 includes a plug 787, sealing gasket 789 and conical washers 791. The ion source block can also be tilted about the axis of support screws 806 by means of a flexible rod 816 which is secured to the front plate 813 of the ion source block. Adjustment of the beams defining plates.- The ion exit plates 1307, 1308, Fig. 30, together with the plates 1311, 1312, can be moved to vary the width of the ion exit slit by swinging support arms 1327, 1333, about a hinge rod 1326 (axis 1319 in Fig. 29). A shaft 1349, Fig. 29, threaded in opposite directions can be rotated by a worm wheel 1362 and worm 1364 to displace the support arms 1327, 1333 simultaneously in opposite directions. The worm 1364 is operated by a mechanism including the universal joints 1376, 1377. The supplementary beam defining plates 1401, 1402, Fig. 30, are carried by arms 1406, 1414 which are tied to the support arms 1327, 1333 so as to be moved at the same time. In addition, the plates 1401, 1402 can be adjusted separately about the hinge rod 1326 by means of rotatable shafts 1425. The shafts 1425 are driven by mechanisms including universal joints 1433, 1435, Fig. 29. Electron emitting filament and adjustable supports.-The electron emitting filament 931, Fig. 29, may be circular or rectangular in cross-section. The filament is supported by clamps 932, 943, Fig. 37, which are mounted on cooling pipes 942, 943. The pipes 942, 943 are within a casing 944 which is mounted for lateral movement by means of a gimbal mechanism 1077, 1062 and a bellows 1079. Motion is imparted to the ring 1077 by a tube 1082. The tube 1082 can be shifted laterally in two directions at right angles by mechanisms each including a rod 1152, Fig. 36, worm wheel 1172, and worm 1174. A spring 1183 acts on the opposite side of the tube 1082. The tube 1082 can be moved axially by means of screws 1247, 1248. A valve 1271 is provided so that the casing 944 can be withdrawn and the filament changed without letting down the vacuum. Adjustments of accelerator mechanism.-The accelerator assembly 1461, Fig. 41, is mounted for universal movement on tubes 1511, 1512 carried by bellows mechanisms 1553. The tubes 1511, 1512 can be moved axially in unison by worm wheels 1578 supported on the bellows 1586. The assembly 1461 can be rocked about axis 1502, and the accelerator plates 1462, 1463 moved individually towards or away from each other by mechanisms 1609, 1648. The mechanisms 1609, 1648 are driven from within the support tubes 1511, 1512. The accelerator plates 1462, 1463 are mounted on leaf springs 1479. Shield plates 1495 are provided. Tank liner.-The tank liner 1666, Fig. 51, has a cooling pipe 1778 which is shaped to cool overheated areas. Leakage at the fittings is drawn off to the vacuum pumps through interior passageways. The liner is adjustable within the tank, Fig. 53 (not shown). Exploratory ion collector.-An ion collector 1801, Fig. 55, principally for testing, consists of a pair of plates 1948, 1949 defining a slot 1950 and has a first target 1961, with a slot 1971 of limited length, which is backed by a second target 1972. Plates 1948, 1949 and 1961 are mounted on individual cooling pipes. The receiver is mounted on a universal bellows mechanism 1836 and can be moved axially by means of screws 1874, 1876. The support tube 1851 may also be rotated slightly, Fig. 62 (not shown). Main ion collector.-The main ion collector which is introduced in place of test collector 1801 consists of a slotted face plate 2029, Fig. 60, backed by lined pockets 2066, 2078. Separate cooling pipes are provided for the face plate 2029 and for the interior plates 2072, 2083. A supplementary ion collector for correctly positioning the main collector is formed by a slotted plate 2117 and the face plate 2029.