US2204388A - Photoelectric tube - Google Patents

Description

' H. STEYSKAL PHOTOELECTRIC TUBE Jl me 11, 1940.

Filed Jan. 28, 1938 M I e e .0 0t m n t ft vw A hm W m e H H Patented June 11, 1940 i azoisss PATENT" orrics I 2,204,388 i PHO-TOEL CTRIUTUBE HerbertySteyska-LlBerlin, Germany, assignor to General Electric. Company, a corporation of NewYork 1 ApplicationJanuary2 8, 1938, Serial No. 187,521

1 Ill Germany March 3, 1937 rea s. 01...2504166) t i The present invention'relates to photoelectric tubes and more particularly to ligh't se'nsitive tubes-which-depend'on secondary electrons for their operation. 7 In the prior tubes ofthis generaltype, -the anode is usually interposed between the primary and secondary cathodes, and is maintained at a potential more pos'itivewith respect to the primary cathode than the secondary emission cathode. anated by the primary cathode when exposed to light necessarily move in the general direction of the anode on their'way to the secondary cathode and in many cases, actually strike the anode. All of the electrons emittedby the primary cathode theref'ore'do not reach'the secondary cathode for the production of secondary electrons and a part of the'amplification which the tube should have islost.

An object of the present invention is to pro vide a phototubeof the secondary emission type and having an electrode structure in which the primary electrons, in their travel toward the secondary emission electrode, do notstrike the anode. Another object is to provide a tube of this character in which the secondary electrons, in their travel toward the'anodetake a'difierent path from the primary electrons in their move ment toward the secondary emissionelectrode. A further object is to provide a phototube of the secondary emission type in which the'anode is interposed between theprimary and secondary cathodes, and the anode field is controlled in such amanner as to cause the anode to attract the secondary electrons butnot the primary electrons. A still further object is to provide a phototube in which. the photoelectrons emitted by the cathode are electrically and physically constrained from impinging on the anode, and only i the secondaryelectrons emitted by'the secondary emitting electrode are permitted-to reach the anode. These objects are attained in brief by providing a shield meniber between the anode and theprimary cathode, the shield being charged to such a potential as to directthe primary electrons away from the anodebut still permit the secondary electrons emitted by the secondary cathodeto reach the anode; The invention will be better understood in connection with the following description and the accompanying draw ing in which'Fig. 1 shows a sectional view" or" a phototube improved in accordancewith' the present invention and connected in arr-energizing circuit. Figs. 2 and- 3 are perspective-views of modifiedformso-f the-improved tube; l igJrshows Consequently, the photoelectrons em- I a still further tube modification; Figs. 5 and 6 are fragmentary sectional views taken along lines 5-5, 65respectivelyin Fig. 1; Figs. 7 and 8 arefragmentarysectional views taken alonglines ducting material, for example copper, mounted in 7 position in'any suitable manner. The interior surface of the electrode 2 is coated with lightsensitive material such as caesiumoxide on silver,

as is shown inv Fig. 6, and applied in any suitable and well-known manner. This electrode when exposed to an external light source (not shown) serves the function of a primary cathode in providing'photoelectrons. As shown in Fig. 5, the inner surface of the electrode 3 may be coated in any suitable and well-known manner with a material such as barium oxide on nickel which profusely emits secondary electrons when struck by primary electrons traveling at a high velocity. The anode of the tube is composed of a metallic body 4 of essentially punctiform character which is supported at a position central of the envelope.

=When the secondary cathode 3 is maintained at a high potential with respect to the primary cathode 2 by means of a battery 5, and the anode is maintained at a still higher potential with respect to the cathode ZQphotoelectrons produced at the inner surface of the electrode 2, when light impinges on this surface, are strongly attracted by the anode and the secondary cathode. The

light may be directed through the opening 6 in the secondary cathode 3, or through the space between the electrodes 2, 3. Those electrons which reach'the electrode 3 give rise to secondary prior art tubes, all of the photoelectrons generated at the electrode Tdo not'reach the secondary emitter electrodefi but instead; some of them go directlyto the anode 4, the amplification obtained is not an'optimum. This diversion of electrons iseliminatedorat least substantially reduced in accordance with the present invention by providinga-shield member or patio 8 rigidly supported in the envelope in any suitable manner While the shield member may take anysuitable shape,- it is preferred to give it and positioned-between the anode and the pri- 'mary cathode.

a configuration similar to that of the primary cathode. The shield may be given any suitable potential, positive or negative with respect to the primary cathode and for this purpose, may be connected to the common source of potential 5. If desired, the shield member may be connected directly to the cathode 2. The electrical effect on the primary electrons introduced by the electrically charged shield member 8 is shown roughly by the dotted line a which indicates the path of a primary electron being diverted from the anode by the shield and moving toward the secondary cathode 3. As stated hereinbefore, for every electron which strikes the secondary cathode, more than one secondary electron may be generated, and the path of these electrons is indicated by the dotted line b which leads directly to the anode 4.

If the anode lead-in connection presents a conductive area comparable to that of the anode proper, it is in some cases advantageous to shield it also. This may be done either by covering it with a layer of insulating material or by providing an extended portion of the shield 8 adequate for the purpose stated.

Fig. 2 shows the application of the improved shields to an elongated cylindrical form of phototube provided with two or more centrally positioned anodes l0. Shields H of a hemispherical configuration may be provided about each anode, as in the case of the single anode tube of Fig. 1. If desired, the anodes may be connected together within the tube to form a loop, in which case a single shield may be employed having such a shape as to be interposed between all parts of the loop and the primary cathode. The primary cathode [2 may take the form of a light-sensitive coating of any suitable material such as caesium oxide on silver. and applied directly to a limited portion of the envelope. The secondary cathode I3 may be of a size comparable to that of the light-sensitive coating l2 but positioned diametrically opposite from the latter. A foundation layer of metal may be applied directly to the glass, and secondary emission material such as barium oxide coated on the foundation layer. This secondary emitter member preferably has an aperture l4 through which light may enter the tube and impinge on the light-sensitive cathode 12. The light might also be directed through the space between the coatings or even through the secondary cathode if it is sufficiently transparent. As in the case of Fig. l, the shields II, when charged to the proper potential with respect to the primary and secondary cathodes, serve to redirect the photoelectrons away from the anodes and to cause them to strike the secondary emitter electrode. A circuit arrangement similar to that shown in Fig. 1 may be employed to provide the necessary electrostatic fields.

The tube shown in Fig. 3 is of the same general type as that illustrated in Fig. 1 except that the primary and secondary cathodes are applied directly to the envelope rather than being constituted of a coating on metal members mounted apart from the envelope. The light-sensitive coating I5 may be constituted of caesium oxide or any other light-sensitive material, and the secondary emitter coating I 6 may be composed of barium oxide or any other suitable secondary emission material. Leads are taken from these coatings to the exterior of the envelope through the reentrant stem [1. The anode may comprise a rigid rod I8 which terminates at the central position of the bulb. The shield l9 may constitute a hemispherical member, as in the case of Figs. 1 and 2, and connections from this member and all of the electrodes taken to a source of current such as a battery (not shown).

Fig. 4 represents a tube somewhat similar to that shown in Fig. 3 in that the primary and secondary cathodes I5, iii are constituted of coatings applied directly to the envelope but in this case, the anode and the electron shield or baflie are constituted of the well-known heater and sputter shield members which would normally be provided in tubes of this sort. In those tubes having a coating applied directly to the envelope, it is customary, as shown in the Ruggles Patent No. 1,568,694, to provide a heater for vaporizing the foundation metal and also to provide a sputter shield for preventing the deposition of the metal on undesired portions of the envelope. In case two separate coatings are employed, as shown in this figure, two heaters and two shields would normally be provided for the purposes mentioned. After the coatings have been applied, the heater and sputter shields could conveniently be used for the regular anode, also as an improved shield for intercepting or diverting the primary electrons away from the anode in accordance with the present invention. However, it would be noted that only the heater designated by the reference character 20 which is further removed from the cathode I5 is in the proper position to be shielded from primary electrons by the immediately adjacent shield l9 and hence, only this heater can be employed as the anode. As in the case of the previous figures, the primary and secondary cathodes l5, l6, also the anode 20 and the shield l9, may be connected to a common source of current which provides the necessary fields within the tube to cause the secondary electron emission and shielding efiects.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A discharge device including a primary cathode of relatively extensive surface area, a secondary emission electrode positioned in spaced relation to the primary cathode to receive electrons therefrom, an anode interposed between the primary cathode and the secondary emission electrode and effective during operation of the device to receive current from the secondary emission electrode, said anode being essentially punctiform so as to offer little physical obstruction to the passage of current from the primary cathode to the secondary electrode, and a baffle interposed between the anode and the primary cathode for shielding the anode from electrons emitted by the cathode.

2. A discharge device including a primary cathode in the form of a partial surface of revolution, a secondary emission electrode also in the form of a partial surface of revolution and positioned in opposite relation to the primary cathode to receive electrons therefrom, an anode interposed between the primary cathode and the secondary emission electrode and effective during operation of the device to receive current from the secondary emission electrode, said anode being essentially punctiform and being positioned approximately at the common center of revolution of said cathode, and secondary emission electrode, and a baflie interposed between the anode and the primary cathode, said baffle interceptingsubstantially all straight lines between the anode and the cathode, thereby to minimize collection by the anode of electrons said anode being essentially punctiform and being positioned approximately at the common center of curvature of the cathode and the secondary emission electrode, and a bafile interposed between the anode and the light sensitive cathode for deflecting electrons emitted from the cathode and proceeding. toward the secondary emission electrodefsaid bafiie being of materially smaller area than the cathode.

- HERBERT STEYSKAL.

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