US2789240A - Cold cathode electron discharge devices - Google Patents

Description

April 16, 1957 M. J. COHEN COLD CATHODE ELECTRON DISCHARGE DEVICES Filed Nov. 22, 1952 INVENTOR. RIIN .1 E UHEN JTI'ORNEY United, States Patent COLD CATHODE ELECTRON DISCHARGE DEVICES Martin J. Cohen, Princeton, N. J assignor to Radio Corporation of America, a corporation of Delaware Application November 22, 1952, Serial No. 322,012

Claims. (Cl. 313-54) This invention relates generally to cold cathode electron discharge devices and particularly to new and improved evacuated cold cathode discharge devices.

Previously, a number of cold cathode electron discharge devices such as cold cathode rectifiers, amplifiers, and the like have been proposed. Many of these devices are structurally complex. Moreover, for their operation, some of these devices require one or more of a gas-filled envelope, a secondary emitter, and means for producing either high magnetic or high electrostatic fields for ionizing the gas. A device of this general type is described in U. S. Patent No. 2,616,986, entitled Cold Cathode Gas-Filled Amplifier Tube and granted to John H. Coleman on November 4, 1952.

While these devices generally are satisfactory, a simpler and advantageous cold cathode device is desirable which requires no gaseous medium or complicated structure associated therewith.

An object of the invention is to provide an improved and simplified cold cathode electron discharge device.

Another object of the invention is to provide an improved and simplified vacuum-type cold cathode electron discharge device.

Another object of the invention is to providean improved v-acuum-type cold cathode electron discharge device for rectifying or amplifying signals input thereto.

Another object of the invention is to provide an improved vacuum type cold cathode electron. discharge device useful for detecting nuclear or other high energy radiations.

A further object of the invention is to provide a new and improved cold cathode for use in devices of the type herein disclosed.

A further object of the invention is to provide a new and improved photoemissive cold cathode.

A still further object of the invention is to provide a new and improved cold cathode device employing a radioactive isotope.

According to the present.invention a cold cathode electron discharge device is hereinafter disclosed and claimed which is operative in a vacuum and does not require the use of magnetic or other deflection circuitry. One feature of the invention is directed to a cold cathode electron discharge device employing 'a photoemitter, initially activated either by dark current signals or by a light source, which cooperates with a phosphor or scintillation crystal positioned in the travel path of the liberated photoelectrons. These electrons are urged in the direction of the phosphor by an accelerating field whereby the phosphor or crystal produces photons of light when bombarded by these photoelec'trons. The light emission induces the liberation of further electrons from the photoemitter. Thus the cooperative action of the photoemitter and the phosphor (or scintillator) results in a regenerative discharge which substantially re- (hides the impedance of the device. Another feature of the invention is directed to a novel cold cathode employing a radioactive isotope which cathode is especially useful in a device of the type described above. The cathode by a physical mixture of radioactive and scintillator 2,789,240 Cfi Patented Apr. 16, 1957 2 material or by a homogeneous scintillator crystal or solid containing a radioactive nuclide -as-a constituent part of its atom. 7

Other features and advantages of the invention will be described in connection with the accompanying drawing in which:

Figure l is a schematic circuit diagram of a vacuumtype cold cathode rectifier, according to the invention;

Figure 2 is a schematic circuit diagram of a further embodiment of the invention wherein signal amplification or radiation detection may be achieved;

Figure 3 is a schematic diagram of another embodiment of the invention similar in part to apparatus illustrated in Figure 1 and employing a novel photocathode; and

Figure 4 is a modification of the photocathode shown in Figure 3.

Similar reference characters are applied to similar elements throughout the drawing.-

Figure I of the drawingshows a cold cathode rectifier device embodying the invention. An evacuated envelope, glass, for example, contains a photoemitter 13 supported by a conductive support member 15. A second conductive member 17 is spaced from the photoemitter 13 and supports, on a surface thereof facing the photoemitter 13, a material 19 which produces light emission when subjected to electron bombardment. The photoemitter '13 may comprise, for example, cesium antimonide or cesium silver oxide. The light emission material 19 is selected to be a material which produces photon energy within the, range of light sensitivity of the photoemitter 13. This material 19 may be a phosphor such as zinc activated zinc oxide, calcium tungstate, zinc sulfide, cadmium sulfide, or alternatively a suitable scintillation crystal, such as anthracene.

To achieve signal rectification one terminal of a source 21 of signals 23 to be rectified is connected via lead 25 to the conductive member '17 which supports the phosphor or crystal 19. The remaining source terminal is connected to ground potential. Initially electrons are liberated from the cathode 13 by some such phenomena as spurious dark current emission within the envelope. in the time intervals during which signals 23 cause support member 17 to swing to a potential positive with respect to the potential of support member '15, an electric field is established between the support members 15 and 17 which causes electrons liberated by the photoemitter 13 to be accelerated toward and bombard the photon emitting material 19. Material 19, in response to this electron bombardment, produces light emissions which further activate the photoemitter 13 and cause additional electron emission therefrom and a voltage to be developed across a load resistor 27 connected between the photoemitter support member 15 and ground.

The cooperative and cyclical action of the photoemitter 13 and the photon emitter 19 result in a regenerative electron discharge within the device and a lowering of its effective impedance during these intervals. In inter vals during which signals 23 cause support 17 to swing to a potential negative with respect to the potential of support member 15 no accelerating field is produced which results in electron bombardment of material 19, the spuriously emitted electrons produced by the photoemitter 13 return to its surface, and the impedance of the discharge device is high. Thus rectification is achieved since during positive potential swings of support member 17 electrons flow from the photoemitter 13 to the support member 17 and the potential across load resistor 27 swings positively; during negative potential swings of support member 17 no electrons leave the photo emitter13 andthe potential developed cross resistor 27 is substantially zero.

The cascade discharge mentioned above may be controlled as desired either by suitable selection of a load resistor by choosing a phosphor or photoemitter which saturates in its light or electron emission at a givenpoint. Also,' in theevent that a more rapid build-up. of thecascade discharge is desired a light source 29 external the envelope 11 may beutilized to enhance electron emission from the photoemitter 13.

Figure 2 shows a cold cathode amplifier embodiment of the invention having a cylindrical configuration. In this arrangement the photoemitter 13 is supported on a conductive rod 15 and is surrounded by a cylindrical conductive member 17 on the inside surface of which the phosphor or scintillator material 19 is disposed. Electrode 17 is connected to a source of positive potential via a resistor 31. A control electrode 33, such as a mesh grid'or other structure, is positioned intermediate the photoemitter 13 and the phosphor 19 and is biased negatively with .respect to the photoemitter support member '15 by a bias battery 35.

In operation the bias potential applied to the device is selected so that a moderate quiescent electron. current flows from the photoemitter 13 to the support member 17. Input signals 37 to be amplified are coupled from a source (not shown) through a coupling capacitor 39 and are developed across a grid leak resistor 41. These input signals 37 modulate the electric field established within the device by the positive potential applied to support 17 and cause the quiescent electron current to be modulated. accordingly. During positive potential swings of the control electrode 33 the device current increases .and the instantaneous potential developed across resistor 31 is large. Conversely, during negative potential swings of the control electrode the device current is reduced and the instantaneous potential developed across resistor 31 is small. An external light source 29 may be utilized in the event that spurious or other light emission is ineffective in initially activating the photoemitter 13.

Although the above device has been illustrated and described as a triodc amplifier, it will be recognized that additional electrodes may be added whereby the device operates as a tetrode, pentode, or the like.

Figure 3 shows a further embodiment of the invention which is similar in part to the apparatus described with respect to Figure l and includes a novel cold cathode. In this example the photoemitter support member and the external light source 29, illustrated in Figures 1 and 2, may be omitted and replaced with a photon source 43 including a radioactive isotope and a scintillation material. The photon source 43 may comprise a homogeneous scintillation crystal or a solid having a radioactive nuclide as a constituent atom thereof, for example, radioactive carbon in anthracene. Alternatively, the photon source may comprise a physical mixture, as shown in Figure 4, comprising a plurality of radioactive emitters 45 having a plurality of layers 47 of scintillation material interspersed with and in contact with the radioactive emitters. The radioactive emissions excite the scintillator to produce photons of light which, in turn, activate the photoemitter 13. The combination of the photon source 43 and the photoemitter 13 thus provide a new and useful cold cathode especially adapted for use in a dediations. In the devices of Figures 1 and 3, for example, a positive potential may be applied to support members 4 17 to establish an electric field within the device. The ambient radiation then excites the phosphor or scintillator 19 to either initiate or enhance the cascade discharge of the device. In this instance the resistor 27 may be replaced with a suitable voltmeter or other device for indicating the intensity of the incident radiation. In the deviceof Figure 2 the light source 29 and the input circuit capacitor 39 may be omitted and the device operated for radiation detection in the manner above described.

What is claimed is:

1. A cold cathode electron discharge device comprising, an evacuated envelope, at photoemitter contained within said envelope, a photon source within said envelope for activating said photoemitter to produce electron emission therefrom, said source including a scintillation material and a radioactive isotope, an element spaced from said photoemitter and responsive to electron bombardment for producing light emissions within the light sensitivity range of, said photoemitter, and an electrode responsive to a potential impressed thereon for accelerating electrons emitted by said photoemitter to bombard said element, said bombarded element thereby producing light emissions causing further electron emission from said photoemitter. 1

2. A cold cathode electron discharge device compris ing, an evacuated envelope, a photoemitter contained within said envelope, a photon source within said envelope for activating said photoemitter to produce electron emission therefrom, said source including a homogeneous scintillation crystal having a radioactive nuclide as a constituent a'tom thereof, an element spaced from said photoemitter and responsive to electron bombardment for producing light emissions within the light sensitivity range of said photoemitter, and an electrode responsive to a potential impressed thereon for accelerating electrons emitted by said photoemitter to bombard said element, said bombarded element thereby producing light emissions causing further electron emission from said photoemitter.

3. A cold cathode electron discharge device comprising, an evacuated envelope, a photoemitter contained within said envelope, a photon source Within said envelope for activating said photoemitter to produce electron emission therefrom, said source including alternate interspersed layers of radioactive and scintillation materials, an element spaced from said photoemitter and responsive to electron bombardment for producing light emissions within the light sensitivity range of said photoemitter, and an electrode responsive to a potential impressed thereon for accelerating electrons emitted by said photoemitter to bombard said element, said bombarded element thereby producing light emissions causing further electron emission from said photoemitter.

4. A cold cathode comprising, in combination, a photoemitter, and a homogeneous scintillation crystal having a radioactive nuclide as a constituent atom thereof for producing photons of light for activating said photoemitter.

5. A cold cathode comprising, in combination, a photoemitter, and a photon source including a plurality of radioactive emitters and a plurality of layers of scintillation material interspersed with and in physical contact with said emitters, said radioactive emitters bombarding said scintillation materials with high energy emissions to produce photons of light for activating said photoemitter.

References Cited in the file of this patent UNITED STATES PATENTS Maurer Oct. 15, 1940

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