US2431507A - Electron multiplier - Google Patents

Description

Nova 25, 1947. l R. D. REILLY 2,431,507 ELECTRON MULTIPLIER A K Filed April 3, 1944 INVENTOR ROBERT D. REILLY ATTORNEY vsurface thereof.

Patented Nov. 25, j 1947 UNITEDVSTATES PATENT OFFICE ELECTRON MULTIPLIER Robert David Reilly, Fort Wayne, Ind., assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application April 3, 1944, Serial No. 529,299

(Cl. Z50-175) 4 Claims.

Y 1 This invention relates to electron multipliers and particularly to devices of this character employed with phototubes.

It is customary for numerous purposes to vemploy phototubes for the purpose of developing electrical energy in response to and in correspondence with received light energy. Despite substantial improvements made in the electron emissivity of such devices, the developed electhereof. A frequently employed amplifying apparatus is an electron multiplier, preferably one having a plurality of secondary electron emissive electrodes.

As is well known in the art, however, it is necessary to locate the first of a series of such multiplier electrodes adjacent to the photosensitive surface of the phototube cathode. Where the surface of the cathode is relatively small and is not required to intercept light from an appreciably wide angle, it is usual to locate the entrance opening of the first multiplier electrode adjacent to the peripheral edge of the cathode. Where the photosensitive surface of the cathode is of considerable area, however, such an arrange'- ment is not completely satisfactory for the reason that a substantial portion of the cathode surface is too remote from the multiplier electrode to enable the acceleration of electrons emitted therefrom toward the multiplier electrode without employing abnormally high accelerating voltages between the cathode and the multiplier electrode.

Such a difficulty is overcome by the use of a A centrally apertured cathode and a multiplier electrode disposed adjacent to the cathode aperture in the space contiguous to the photosensitive Such a structure forms the subject matter of a copending application" of L. G. Wolfgang, Serial No. 537,953 filed May 29, 1944, and entitled Photocell multiplier tube.

The structural arrangement disclosed in the copending Wolfgang application referred to is a substantial improvement over devices previously used. However, for some uses of phototube vmultipliers it has the disadvantage that the multiplier electrode is in a position to obstruct some light directed toward the phototube at an angle tothe cathode surface. It sometimes is rnecessary to y employ a phototube multiplier capable of responding `to light received from any source within a substantial angular zone with respect to the phototube. In order that such a device be capable of producing a maximum response to the received light it is necessary that the phototube multiplier be constructed so that none of the received light is prevented from reaching the photosensitive surface of the cathode.

It is an object of the present invention, therefore, to provide a phototube multiplier having a novel structural arrangement of the component electrodes, whereby substantially all of the light received from a zone angularly related to the device is utilized to actuate the device.

In accordance with the invention, there is provided a phototube device having a cathode in which is formed an aperture. An electrode which bears an anodic relationship to the cathode is disposed on the side of the cathode which is remote from the photosensitive surface thereof. This anodio electrode is provided with an auxiliary electron and light pervious electrode which is electrically connected thereto and which extends through the cathode aperture into the space contiguous to the photosensitive surface of the cathode.

For a better understanding of the invention. together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

The single figure of the drawing is a longitudinal cross sectional view of a phototube multiplier embodying one form of the invention.

Referring now to the drawing, the phototube multiplier is enclosed in an evacuated envelope i. A cathode 2, having a concave photosensitive surface of considerable area is mounted in the envelope in such a manner that the photosensitive surface is adjacent to and faces a transparent end wall of the envelope. The cathode is provided Ywith a centrally disposed aperture 3. The eleodesired shape, such as a substantially cylindrical:

configuration, as shown.

An electron collecting electrode 'I is located-adjacent the exit opening of the .other Vend one 5 The.

of the plurality of multiplier electrodes. collecting electrode may have any desired shape, such as the disk configuration shown.

The cathode, the multiplier electrode and theI collecting electrode are connected electrically iny a Well known manner to a, conventional source lof' energy (not shown). These connections are made lthrough the press portion 8 of the tube envelope. If desired, the 4conductors extending `through the tube press to the tube electrodes may be of relatively heavy gage Wireso that they serve also as the supporting means for the electrodes.

If desired, the ,cathode 2 may also be provided with a screen 9, which is electrically connected to and supported by the peripheral edge of the .cathode.

Referring now tothe operation of the phototube multiplier embodying ,the present invention, it is assumed that the usual voltages are impressed upon the tube electrodes. For example, the multiplier electrode 4 and its auxiliary per- .forate electrode `l hasapplied thereto a voltage ofthe order of a hundred vo-lts positive with respect to the cathode 2 and the collecting, elec,-

trons from every unit area of the cathodein numv bers corresponding to the quantity of light fall'- ing upon the respective areas, These emitted electrons have relatively loW velocities. I n order to effect the impingement ,of these electrons upon the rst stage multiplier electrode, it is ,necessary tolcreate an ,accelerating field of suicient scope and strength to influence all of the electrons emitted from the cathode. Such a eld is produced by the auxiliary perf crate electrode 6. This electrode extends sufficiently Within the space ,contiguous `to the photosensitive surface of the cathode to attract electrons emitted Ifrom any portion of the Cathode surface. The emitted `electrons, therefore, are accelerated toward the perforate electrode and substantially all of them pass through the meshes or perforations lof this electrode. Thence they are dravvn toward the secondary electron emissive ,surface of the first stage multiplier electrode 4 upon which they imtrons ultimately is collected by the collecting electrode 'I to which may be connected any desired utilization circuit.

By reason of the novel structural arrangement of the phototube multiplier in accordance with this invention, there is produced a. device which has large light gathering proper-ties and one in which maximum. utilization is made of the received light, The large surface area of the phototube cathode provides the device with large light Igathering properties. The disposition of the electron multiplying apparatus on the side of the cathode remote from the photosensitive surface thereof insures that none of the incident light tvililaloe obstructed thereby- The provision of the perforate electrode 6 enables the use of substantially a-ll of the photoelectrons emitted by the cathode, Also, by reason of its perforate configuration, it offers substantially no obstruction to light, despite the fact that it is located vin the space contiguous to the photosensitive surface of the cathode.

While there has been described what, at present, is considered the preferredv embodiment o f the invention, it will be obvious to those skilled in theart that various changes and modifications maybe made therein Without departing from the invention, and therefore, it is aimed in the appendedclaims to cover all such changes and modifications as Vfall within the true spirit and scope of the invention.

`What is claimed is:

1 A phototube multiplier comprising, a cathode having a concave photosensitive surface and a ,centrally disposed aperture formed therein, a .secondary electron ,emissive multiplier electrode disposed -on the side of said cathode remote from the photosensitive surface thereof adjacent t0 said cathode aperture, a perforateelectrode electrically connected to said multiplier electrode and extending through said cathode aperture into the space contiguous to the photosensitive surfacecf s aid cathode, and an electron collecting electrode disposedin spaced relation to said multiplier electrode and adapted to receive electrons .emitted under the control of said multiplier electrede.

2. A phototube multiplier comprising, a. cathode. having a concave photosensitive surface and a centrally disposed aperture formedtherein, a ,box-type secondary electron emissive multiplier electrode disposed on the side of said cathode remote from the photosensitive surface thereof adjacent to said cathode aperture, a field producing yscreen electrically connected to said multiplier electrode and extendingA through said cathode aperture into the space contiguousy to the photosensitive 4surface of said cathode, and an electron collecting yelectrode disposed in spaced relation to said multiplier electrode and adapted tiplier electrode and extending through said cathode aperture into the space contiguous to the photosenstive surface of said cathode, said screen electrode serving to produce a field for attracting cathode-emitted electrons toward said aperture, and an electron collecting electrode disposed adjacent to said second multiplier electrod@ and adapted to receive electrons therefrom.

4. A phototube multiplier comprising, a cathode having a concave photosensitive surface of considerable area and a centrally disposed aperture formed therein, a plurality of box-type secondary electron emssive multiplier electrodes serially arranged on the side of said cathode remote from the photosensitive surface thereof, first and second ones of said multiplier electrodes being disposed respectively at opposite ends of said serial arrangement, said first multiplier electrode being disposed adjacent to said cathode aperture, a substantially cylindrical screen electrically connected to said first multiplier electrode and extending through said cathode aperture into the space contiguous to the photosensitive surface of said cathode, said screen 6 serving to produce a field for accelerating cathode-emitted electrons toward said rst multiplier electrode, and an electron collecting electrode disposed adjacent to said second multiplier elec-,- trode and adapted to receive electrons therefrom.

ROBERT DAVIDr REILLY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,198,233 Snyder, J1'. Apr. 23, 1940 2,227,095 Liebmann Dec. 31, 1940 2,171,233 Ericksen Aug. 29, 1939 2,218,744 Colberg Oct. 22, 1940 2,163,966 Snyder June 27, 1939 FOREIGN PATENTS Number Country Date 499,661 Great Britain Jan. 26, 1939

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