US2715196A - Electron emitter - Google Patents

Description

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E umm w j 2 7 w Aug. 9, 1955 J. D. REID ELECTRON EMITTER Filed Feb. 21, 1946 United States Patent O ELECTRON EMITTER John D. Reid, Oak Ridge. Tenn., assgnor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application February 21, 1946, Serial No. 649,404

1 Claim. (Cl. 313305) This invention relates to electron emissive and related devices, and it is particularly concerned with a secondary electron emitter, that is, a secondary emitter which is rendered emissive by being heated as a result of being bombarded by electrons emitted from a primary emitter. The invention finds particular adaptability in ion sources ordinarily used in calutrons, that is, in the electromagnetic type of apparatus which is used for separating isotopes. ln this type of ion source, a vapor of a material the isotopes of which are desired is bombarded in an ionization chamber by electrons emitted by an emissive device. In calutrons it is often desirable to use a primary and secondary emitter. The secondary emitter produces the stream of electrons which bombards the vapor in the ionization chamber. The secondary emitter is subject to conditions which experience has shown tends to make it very short lived requiring frequent replacement and renewal.

The primary object of my invention is to provide a secondary emitter having characteristics calculated to give it longer life and to make the emitter extremely easy of replacement and renewal.

Another object of my invention is to provide a secondary emitter of the type referred to above so constructed and arranged as to provide for the maximum of ease in assembly and disassembly.

Another object of my invention is to provide a secondary emitter having very simple, convenient, efficient, and easily fabricated means for insulatively mounting the emitter.

Another object of my invention is to provide a secondary emitter comprising a yoke having apertures in the arms thereof with a transverse member having its ends tted into the apertures, the arrangement providing for removal and replacement of the transverse member by springing apart of the arms of the yoke.

Another object of my invention is to provide an arrangement as in the preceding object wherein the yoke is made of molybdenum and the transverse member is of tantalum.

Another object of my invention is to provide a mounting for a secondary emitter or the like consisting of screws and Lavite nuts, the nuts being countersunk in the base member upon which the emitter is mounted.

Further objects and numerous of the advantages of my invention will become apparent from the following detailed description and annexed drawing wherein Fig. l is a front View of the emitter of my invention. Fig. 2 is a sectional side elevation of the emitter of Fig. l taken along line 2-2 of Fig. l, and Fig. 3 is a diagrammatic perspective view showing a primary emitter, the secondary emitter of my invention and an anode in the relative positions which they would normally occupy.

Referring to Fig. 1 of the drawing, the emitter comprises a stainless steel strip of metal 3 which is bent at its upper end as shown in Fig. 2, and attached to the upper end of this strip by soldering or the like is a U-shaped yoke member 2 which is made of molybdenum.

2,715,196 Patented Aug. 9, 1955 ICC The arms of the yoke member have apertures as shown at 9 and fitting in these apertures are the ends of a transverse rod member 1 the ends of which are tapered. The rod 1 constitutes the electron emissive element, it being made of tantalum. It will be noted that one end of the rod 1 has a slightly longer taper than the other end, and the arms of the yoke 2 are suiciently resilient to permit of springing them apart for easily removing the rod 1 and replacing it with a new one.

The plate 3 is attached to a base or panel 10 by means of a flat-headed screw 6 and a round-headed screw 7, the flat-headed screw 6 extending through an elongated opening 11 as may be seen on Fig. l. The round-headed screw 7 extends through an enlarged opening 12 and a washer 13 is between the head of the screw and the plate 3 as shown. Due to the opening 12 being larger than the screw 7 and the opening 11 being elongated, when the screw 7 is loosened, the plate 3 can be adjusted up and down and then resecured. The screws 6 and 7 screw into nuts 5 and 14 which are made of a suitable insulating material and each of which is in the shape of a truncated cone, the nuts being counter-sunk in correspondingly shaped countersinks in base or panel 10. Numeral 8 designates a strip of insulating material which is interposed between the plate 3, the panel 10 having openings therein through which the screws 6 and 7 pass. In this manner the plate 3 of the emitter is securely attached to the base 10 and is kept insulated therefrom, there being no protruding parts, particularly parts of insulating material protruding from the face of the panel 10. That is, the nuts 5 and 14 fit completely into the countersinks and are therefore protected from breakage.

Referring to Fig. 3, the secondary emitter of my invention is shown adjacent the primary emitter 15, that is, a iilamentary cathode which has a voltage V impressed across the terminals thereof. A grid in the form of a plate 18 having a slot as shown is between the primary and secondary emitters. Primary emitter 15 emits a stream of electrons which bombards the tantalum rod 1 of the secondary emitter after passing through the slot of grid 18, thereby raising the temperature of rod 1 suiciently to render it emissive, and it in turn emits a stream of electrons which, in the diagrammatic representation of Fig. 3, bombards an anode or anode plate 16 supported by a stem 17. In applications where the secondary emitter is subject to severe conditions of usage resulting in rapid erosion and short life of the emitter, my invention is particularly useful for the reasons pointed out in the foregoing in that the replacement and renewal is extremely easy, being eected simply by spreading the arms of the yoke 2 apart, removing the eroded rod 1 and replacing it with a new one.

Both the vertical and horizontal adjustment of the secondary emitter can be conveniently made, simply by loosening the screws 6 and 7 and then moving the strip 3 upwardly for vertical adjustment or rotating it about the screw 6 for horizontal adjustment.

From the foregoing those skilled in the art will observe that I have provided a very convenient and efficient device adapted for use as a secondary emitter or in other ways as an electron emissive device. The arrangement of my invention provides for quick and convenient replacement and is mounted in a manner providing for very effective insulation of the emitter and adjustment thereof.

The embodiment of my invention disclosed herein is representative of its preferred form. The disclosure is to be interpreted in an illustrative rather than a limiting sense, the scope of the invention being determined Ain=V accordance with the claim appended hereto.

I claim:

In electromagnetic isotope separating apparatusgxion-` 3 4 producing rmechanism vcomprising an electron emissive 849,159 Parker Apr. 2, 1902 filame'ntiny the form of a cylindrical tantalu'r'n rod hav- 1,816,194 Power July 28, 1931 ing tapered ends, the taper on one of said ends being 2,030,435 Fehse et al. Feb. 11, 1936 longer than the taper onthe other of said ends, means 2,171,238 Gustin Aug. 29, 1939 v for rbombardi'ng said filament with 'electrons to heat said 5 2,350,270 Atlee May 30, 1944 filament to electron emissive temperature, and a yoke member of molybdenum having apertures in Vthe legs REFERENCES thereof forreceivng the tapered ends of said filament, General EleCUC RCVIeW, M3rCh1923, PP- 154-160- said yoke'rnember being resilient to provide for springing'. apart the legs thereof to facilitate removal and re- 10 placement of said rod.

References Cited in the le of this patent UNITED STATES PATENTS 258,976 Bernstein June 6, 1882

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