US2208938A - Divided stream electron multiplier - Google Patents

Description

July 23, 1940.

R. L. SNYDER DIVIDED STREAM ELECTRON MULTIPLIER Filed April 30, 1937 Z'F ig. L.

v IN V EN TOR RICHARD L. SNYDER.

BY v

A TTORNEYS.

Patented July 23, 1940 UNITED STATES PATENT OFFICE DIVIDED STREAM ELECTRON MULTIPLIEB.

tion of Delaware Application April 30, 1937, Serial No. 139,949

4 Claims.

My invention relates to electron multipliers, and more particularly to an electron multiplier wherein the electron stream is divided.

Among the objects of my invention are: To

provide an electron multiplier wherein electrons are separated into two divergent streams in order to reduce space charge effects; to provide an electron multiplier of symmetrical structure; to provide an electron multiplier having a shielded input; to provide a means and method of electron multiplication to the end that space charge limitations are reduced; and to provide a simple and efiicient means and method of electron multiplication.

16 My invention possesses numerous other objects and features of advantage, some of which, together with the foregoing, will be set forth in the following description of specific apparatus embodying and utilizing my novel method. It is therefore to be understood that my method is applicable to other apparatus, and that I do not limit myself, in any way, to the apparatus of the present application, as I may adopt various'other apparatus embodiments, utilizing the method,

5 within the scope of the appended claims.

In the drawing:

Figure 1 is a longitudinal sectional view showing one preferred embodiment of my invention.

Figure 2 is a. circuit diagram showing one way in which the tube of Figure 1 may be connected for operation.

It is obvious that in all electron multipliers wherein electrons are serially directed against a plurality of surfaces capable of emitting secondary electrons at a ratio greater than unity upon electron impact therewith, that as the electrons progress from surface to surface the space between the electrodes ofhigher potential becomes crowded with electrons until space charge limi- 'tations prevent further multiplication. I have found that such limitations may be greatly re duced by dividing the electrons, preferably after the first secondary producing impact, into separate streams, and thereafter separately multiplying each stream. After the proper amount of multiplication has been secured the two streams may be separately collected and recombined in a single work circuit, or, if desired, utilized for different purposes. Each electron path therefore carries only one-half the total current of the device, and therefore the device will not be subject to space charge limitation as soon as if all the multiplied electrons were traveling the same general paths. One apparatus embodying my new method is illustrated herein.

In Figure 1 an envelope l is provided at one end with a reentrant stem 2 carrying an input assembly including a thermionic cathode 3 heated by a heater filament 4. Emission from the thermionic cathode 3 is controlled by a control grid 5 5, fined the control grid 5 is surrounded by shield gri A multiplying assembly is supported by a band 1 clamped to stem 2 by upright risers 8. This assembly comprises a tubular cathode 9, having 10 its inner surface sensitized toprcduce secondary electrons at a ratio greater than unity. This sensitization may take many forms, but for high emission ratios may be caesium on silver oxide. Tubular cathode 9 has a plurality of support ex- 1 tensions l0 adjacent each end thereof, sealed in glass beads ll. Also sealed to glass heads at each end of the open tubular cathode 9 are support extensions l2 of a pair of apertured collecting electrodes I4, one electrode extending across one 20 end of the tubular cathode and the other extending across the opposite end. Immediately back of each apertured collecting electrode is a disc cathode l5 sensitized as the tubular cathode, also provided with support extensions 16 extendg5 ing into beads ll. Thus, the tubular cathode, the collecting electrode, and the disc cathodes are locked in relative positionby beads II. The two collecting electrodes M are connected together by conductor link 20 and the two disc cathodes are to connected together by connecting link 2|. Outside connection is made to the combined collecting electrodes through output lead 22 sealed through a stem 23 at the upper end of the envelope, and a disc cathode lead 24. is sealed as through the samestem.

At one end of the cylinder the appropriate electrode l4 and the adjacent disc cathode I5 are provided with central apertures 25 through which leads 26 to the input assembly may pass, thus y positioning the input assembly co-axially with respect to the tubular cathode 9.

In operation the device may be operated in one manner as shown in Figure 2. Here the heating source for heater filament 4 is not shown, 45 but the connections thereto are well known to those skilled in the art. The thermionic cathode 3 is connected to ground through lead 30. Input grid 5 is supplied with signal energy from input lead 3|. Screen grid 5 is provided with a posiac tive potential from source 32 through lead 34. The tubular cathode 9 is still more positively energized by additional source 35 through lead 35. The two disc cathodes l5 are energized to a still higher positive potential by additional source 63 31 through lead 39, and output electrodes M are held still higher in potential by final source 40 connected to the output electrodes l4 through output resistor M, the output of the device being made available in a work circuit through output lead 42. If separate output circuits are desired for each collecting electrode, separate leads. are brought out to source 40 and an output resistor is placed in each lead.

In operation, electrons are emitted from cathode 3, and are accelerated through the grids to impact the interior surface of the tubular electrode. Upon hitting the interior surface of the tubular cathode secondary electrons are emitted at a ratio greater than unity, and this stream of secondaries divides. Those secondaries near the open ends of the tubular electrode are acceleraated out through the adjacent ends and through the apertured collecting electrode to impact the disc cathodes l5 and thereby generate more secondaries which are collected by the adjacent collecting electrodes. The electrons impacting the tubular electrode near the center thereof may go in either direction, as shown by electron path line 44 in Figure 2. By thus separating the secondaries produced in the interior of the tubular electrode I'greatly reduce space charge effects in the succeeding multiplying stages.

It is obvious, however, that while I have shown only one additional multiplying stage following the tubular cathode, that any number of stages may be operated utilizing the electrons leaving opposite ends of the tubular cathode 9, and any of the well known series of multiplying surfaces may be utilized thereafter.

Such variations in the practice of my new method, and in apparatus equivalents will be immediately apparent to those skilled in the art, and will be deemed to fall within the scope of the appended claims.

I claim:

1. An. electron multiplier comprising an envelope containing a tubular cathode capable of emitting secondary electrons at a ratio greater than unity upon electron impact therewith and having open ends, an apertured electrode adjacent and extending across each open end, a secondary emlsslve cathode back of and parallel to each apertured electrode, said tubular cathode, secondary emissive cathodes and apertured electrodes being energized in the order recited to increasingly higher potentials, and means for liberating primary electrons along the axis of said tubular cathode.

2. An electron multiplier comprising an envelope containing a source of electrons, means for modulating electrons from said source in accordance with desired signals, an electrode having a surface capable of emitting secondary electrons at a ratio greater than unity upon electron impact therewith, means for directing modulated electrons from said source against said electrodeto produce secondary electrons, means emitted from each of said intermediate electrodes, and a single work circuit connected to utilize all of the collected electrons.

3. An electron multiplier comprising an envelope containing a hollow open ended cathode having the interior surface thereof capable of emitting secondary electrons at a ratio greater than unity upon electron impact therewith,

means for liberating primary electrons along the axis of said cathode, and means for accelerating secondary electrons produced by primary electron impact with the interior surface of said cathode simultaneously out of both ends of said cathode.

4. An electron multiplier comprising an envelope containing a hollow open ended cathode having the interior surface thereof capable of emitting secondary electrons at a ratio greater than unity upon electron impact therewith, means for liberating primary electrons along the axis of said cathode, and means for accelerating secondary electrons produced by primary electron impact with the interior surface of said cathode simultaneously out of both ends of said cathode, in substantially equal amounts.

RICHARD L. SNYDER.

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