DE2456596A1 - ELECTRON DISCHARGE ARRANGEMENT - Google Patents

Description

775ο - 7k / Dr, G / Kr

RCA 63 552

Convention Date: November 29 »1973

RCA Corporation New York N.Y. V.St.A.

· »Unloading arrangement

The present invention relates to electron discharge assemblies having at least two electron-optically aligned Electrodes, wherein at least one first electrode having an electron-emitting surface region and an anode is provided, and means around the electrons emitted from each of these surface areas to accelerate in a stream of electrons, which in a non-repeating sequence from the first electrode to the following, aligned electrodes and finally flows onto the anode for collection. In particular concerns describe the present invention arrangements using electron multipliers.

Electron multipliers are commonly used in electronic Image pickup tubes and used as amplifiers in photomultiplier tubes located in the tubes. An electron multiplier is an arrangement in which secondary electron emission is used to reduce the from an electron source, for example a photo or

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To amplify or multiply the electron current generated by the hot cathode. The usual electron multiplier has a Row or a series of secondary emission electrodes or dynodes, which between an electron source and one accept the multiplied electrons Collective electrode are arranged. The dynodes consist of secondary emitting material or are made with secondary emitting material The material is coated and subjected to higher voltage values from dynode to dynode.

Electron multipliers are particularly well suited for amplifying electron currents caused by weak signals ) can be generated, for example, by light or by nuclear radiation. Photomultiplier tubes therefore use electron multipliers, to amplify the electron currents resulting from weak light input signals. With these Arrangements, however, it is only possible to a limited extent to focus the information-essential partial signals and on different parts of the entrance area hit, intensify evenly. For example, the effective photosensitive areas can be determined Photomultiplier tubes, for example in the case of tube housings with a round cross-section, are only parts of the total area available be the photocathode. Bad collecting properties at the The first electrode of such a device can contain the information-essential partial signals of the input signal destroy. In addition, electron multipliers can be used in because electrons skip steps, undesired photoelectronic partial pulses occur in the output signal.

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To those skilled in the art of electron discharge devices various design options for electron multipliers are known. In such arrangements, for example the dynodes can be arranged in a housing with a round cross-section, as shown in FIG. 1 of the present documents is shown, but the dynodes can also be arranged as staggered or staggered longitudinal rows of dynodes, as shown in U.S. Patent No. 2,908,840. In the same Various other arrangements of the photomultiplier tubes are also wise known. For example, such tubes can be those shown in FIG. 1 of the present document Have a "front" structure in which the light is "frontal" is focused and is noticeable on the circular part of the array; or the tubes can have the "side" construction, at which the light is focused "laterally" and through a transparent side of an evacuated housing passes through and then on a photo-emitting surface (the can be applied to an electrode corresponding to electrode 20 in FIG. 1 of the present documents), as shown in U.S. Patent 2,702,865 issued February 22, 1965 is.

In general, the known electron discharge arrangements, as described above, either a curved or a flat electron-emitting electrode, on the electrons coming from an electron source focused, or on which light is directly focused. Regardless of the way in which the electron emission process in this electrode (hereinafter referred to as "first Electrode "designated) is triggered (i.e. regardless of whether there is photo emission or secondary electron emission), was in the output signal of the respective known arrangement,

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i.e. their respective anodes have a considerable degree of uniformity detected when the incoming energy radiation sweeps over the first electrode.

It is therefore, inter alia, an object of the present invention to reduce this uneveness.

This task is performed in the case of the electron discharge arrangement mentioned at the beginning solved according to the invention in that the surface area of the first electrode has a cross-sectional area with an essentially undulating curved line has, which is formed by a plurality of adjacent arc areas.

Further features and refinements of the invention are shown in characterized the subclaims.

The invention, as well as further features and advantages are explained below, for example in detail, with reference to the drawings. Show it

Figure 1 is a cross-sectional perspective view of a photomultiplier tube incorporating one utilizing the invention Electron multiplier in one, a circular one Housing having a cross section;

Figure 2 is a schematic representation of part of Arrangement according to FIG. 1, which shows the shape and the arrangement of the electrodes in relation to one another in the electron multiplier;

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Figure 3 is an enlarged schematic representation of a the electrodes shown in FIG. 2;

FIG. 4 a and k b the comparisons of the sensitivity uniformity of the photomultiplier tube shown in FIG Electrode mounting plates 18 a and 18 b of the electrode multiplier shown in FIG. 1 are given; and

Figure 5 is a perspective view of a modified, annular focusing electrode used in the photomultiplier tube shown in FIG can.

FIG. I shows an embodiment of an electron discharge arrangement according to the invention, a photomultiplier tube 10 with a cylindrical tube bulb 12. The tube bulb has an evacuated glass jacket with a ceramic base lh sealed in itself at one end of the tube bulb * A semitransparent photocathode 16 is formed on the inner surface of an end portion 11 of the tubular piston 12.

An electron multiplier 17 is mounted inside the tube 10. Between two parallel ceramic plates 18a and 18b holding the electrons, dynodes 20-38 and an anode k'O of the multiplier 17 are fixed ^{in a circular arrangement nemi.} The corresponding

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Electrodes extend in a direction perpendicular to the plane defined by the plates l8 a and l8 b (i.e. the electrodes extend perpendicular to the cross-sectional plane of the tube Io shown in Figure 1).

An annular focusing electrode 42 with two after upwardly directed edge parts 42 a and 42 b is arranged between the photocathode l6 and the electron multiplier 17. The ring 42 has a substantially U-shaped cross section. The ceramic plates l8 a and l8 b are on the ring 42 secured by pins 44 and 46 projecting through slots in ring 42 so that plates and focus ring form a uniform component

Several lead-through pins 48, which pass through the tube base 14 in a vacuum-tight manner, create the electrically insulated ones Leads to the interior of the tube 10. Each of the pins 48 is in the tube 10 with a corresponding electrode electrically connected. For example, is the photocathode 16 over the wire 50 and an aluminized layer 52 with connected to one of the pins 48, the aluminized layer 52 on the upper part of the cylinder inside around the tube piston is attached around. The aluminized layer 52 acts as a Shielding and is for the electrostatic focusing of the electrons between the photocathode l6 and the electron multiplier 17 of the device provided when it is connected to the operating voltage,

During the operation of the tube 10, the semi-transparent one is used Photocathode l6 as a source for the electrons that are released when incident of light to be emitted onto the photocathode. These photoelectrons are made by the electron optics that are between

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the cathode 16 and the electron multiplier 17 are present are, electrostatically focused. Suitable electrostatic fields are generated in this area of the tube by the aluminum Layer 52 and the focusing ring 42 created, the electrons being accelerated through an opening 54 in ring 42 if on the corresponding connecting pins 48 suitable voltages are present. The opening 54 is preferably covered with a grid 43 that allows the electrons to pass through, which forms part of the electron-optical focusing arrangement} such a grating is not necessary, however and can also be omitted without significantly affecting the operation of the device.

The photoelectrons emitted by the electron source-16 are then focused and hit an electron emitting surface 56 of the first dynode 20 of the electron multiplier 17 on. The surface 56 consists of one of the known materials for the secondary emission and has for example, a beryllium oxide layer 56 a on one Copper-beryllium pad 56 b. This secondary emitting Material releases several secondary electrons per incident electron or per primary electron. These emitted Electrons are accelerated and hit a correspondingly composed secondary emitting Surface 58 of the next dynode 22, each these electrons generate further secondary electrons. This process is carried out one after the other for each subsequent Dynode 24 - 38 repeated. In this way, the electrons that are at the low potential input side of the electron multiplier occur, multiplied successively by secondary electron emission at each dynode 20-38. A

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electric (electrostatic or magnetic) field accelerates the secondary electrons from one dynode to the next following diode. Those emitted by the last dynode Electrodes are collected by an anode 40.

FIG. 2 shows an enlarged cross-sectional view of the new electrode 20 and its position in relation to the electrons immediately following in the arrangement. In FIG. 3, an even further enlarged representation of the electrode 20 is shown. The E3 electrode 20 has an essentially L-shaped cross section with partial areas L 1 and L 2 (see Fig. 3) The area L 1 serves as an electrostatic shield and creates the necessary field potentials in areas between the dynodes 20, 22 and 2 ^Z ± to focus the electrons between these dynodes. Typical electron trajectories are shown in FIG. 2 by the dashed lines 16. Since the area L 1 can be replaced by a correspondingly acting part, for example by a separate (electrostatic or magnetic) focusing arrangement, the sub-area L 1 is not necessarily part of the electrode 20.

In contrast to the shape of the known electron-emitting surfaces, the new electron-emitting surface of the section L 2 shown in cross-section is provided with a contour that is undulating in cross-section, this contour having several connected or merging arcuate areas. In the main, the new electron-emitting surface has two ^{arc areas connected to one another, which are defined by the angles 0} ^ - and Ύ ", as well as the corresponding radii r and r

1 do

are set.

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The arc areas do not need to be precisely matched to the cross-sectional contour of the electron emission surface. For example, the arc region defined by the angle V ″ in FIG. 3 has a region defined by the angle V - / 3, which in turn has a _{straight line part extending from the point C 0} to the point G. Such slight deviations from the undulating contour of the electron-emitting surface are permissible as long as a sufficiently large number of the electrons emitted from this area are captured by the subsequent electrode (ie strike the subsequent electrodes) geometrical modifications of the contour can be made without significantly affecting the operation of the device.The relative sizes of the radii r and r and the angles ⁰ ^ - and Y (and / or ß ) can be according to the dimensions and arrangements of the device contained different electrodes in a corresponding proportion ality ratio can be selected, as will be described below.

It is important that the electron emission electrodes have a selected cross-sectional shape, as described above was easily incorporated into known electron discharge devices as previously described, built in in order to make the electron current emitted by the first electrode essentially independent from the respective emission points for the different Electrons along the cross-sectional contour essentially be collected uniformly #

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V7ie shown in Figure 2, the electron current generated by secondary electron emission along the electron-emitting surface 56 of the area L 2 of the electrode 20 is accelerated and accelerated by the electron optics of the structure (which is mainly achieved by the electrons 42, 20, 22 and 2k ) focussed and impinges on the electron-emitting surface 58 of the electrode 22 for further electron multiplication within the device, as has been described above. Additional focusing electrodes, for example the rod electrode 62, can additionally be part of the structure in order to contribute to optimal electron optics so that the electron flow between the successive dynodes is accelerated and the electrons are optimally captured at the anode.

It became an embodiment of the photomultiplier tube described about 3.8 cm in diameter and a length of 12.5 cm built and tested. The decisive, essential dimensions and the relative position of the electrodes were made with the help of a coordinate system that defines the dimensions in cm and where the coordinates (X, Y) refer to the zero point shown in FIG Refer to "0". The associated points and the other variables were given as follows:

Photocathode l6: a. (0.0; 5.70); a _o (3.51; 5.70) focus ring k2:

b _t (0.14; 2.58); b _fl (3, ^ 5 2.58)

b ₃ (3, ^; 3,2Ο); t> 4 (0.1 ^; 3.20)

b ₅ (2.39; 2.79); b ₆ (1.195 2.79)

b _? (2,3952.5 ^); bg (1.12; 2

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Dynode 20: C ₁ (2.31j 1.54)

c ₂ (i, 85ji, 5i); c '(1,50,1,57-)

c ₄ (1,3051,52) ϊ c ₅ (i, i4ji, 65)

c ₆ (1, ΐ4; 2.45); ei = 52 ° 15 '; R ₁ (2, o3; 2.ol)

^ ₁ = 0.535 β = 22 ° 15 "; R ₂ (1.47f 066)

r ₂ = 0.90; y = 35 °

cT = 75 °; R. (i, 27il _? 65); r _Q = 0.13

Dynode 22: d _± (2 _f 92il _v 85); d _g (2 ^ 44 * 2 _r 34) R ^ (2.58; 2.00), r ^ = 0.38

Dynode 24: e _± (2.36 _; 1.88); e ₂ (2 _f 54il _f 32)

The cathode Tfurde is made and made in the usual way from a K Cs Sb (potassium-cesium-antimony) material with photo emission effect. The secondary electron emission electrodes were suitably made of a 0.1 cm thick copper-beryllium material. Of the The construction and the arrangement of the photo multiplier corresponded in the other points essentially to the RCA photo multiplier tube type 4517 and other corresponding ones on the Types available on the market.

In FIGS. 4 a and 4 b, the data of the comparative tests are shown and the uniformity of the recording of the new photo multiplier described here (solid Curves 72, 73> 74, 75, 84 and 85) compared to Receipt of the RCA photomultiplier tubes of type 4517 (dashed curves 7 °, 71 »80, and 81). the FIGS. 4 a and 4 b show the experimental data of the relative sensitivity which were obtained when scanning with a Small diameter light source (about 1 mm) and constant intensity across the center line of the surface covering the

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Photocathode 16, were obtained for each of the devices tested. The curves of FIG. 4 a give the sensitivity values for scanning with the light source in an x 'direction, which corresponds to the planes defined by the

“ _N reads in parallel

supports Io a and Io b set sxnd, / C parallel scans ), and the curves of Figure 4b show the scans with the light source in a direction perpendicular to the planes defined by the spacers lö a and l8 b (i.e., perpendicular scans).

Curves 70, 72, 74, 80 and 84 represent the "cathode dept as t "curves, these are the scanning curves that are obtained if the non-photo-emitting electrodes of the corresponding arrangements are switched so that they are used as anodes works. These samples reflect the anode signal current with relative sensitivity, if the appropriate arrangement operated as a photodiode. These cathode scan curves give a visual representation of the uniformity the inclusion of each corresponding cathode when that cathode is scanned.

Curves 71, 73, 75, 81 and 85 are the "anode scan" curves, i.e. they are the sampling curves of the anode signal current which are obtained by considering the respective arrangements under the normal, recommended operating conditions.

If there is uniform scanning sensitivity, then must the corresponding anode scan curves in general practically correspond to the shape of the curve which also corresponds to the cathode scan curves show the same arrangement. In general, the known photomultiplier tubes have a relative low uniformity of sensitivity when using a uniform light source is scanned across the diameter. For example, the dashed anode

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Scanning curves 71 (parallel scanning) and 81 (sonic right scanning ) for the RCA tube 4517 for the same; arrangement ex-visibly different forms than the dashed cathode scanning curve 7 ° biaw. 8o. In contrast, the anode scan test data show obtained with the new photomultiplier tube and represented by the solid curve 73 will, the major improvement in uniformity the recording of the arrangement when this curve is compared with the corresponding cathode scan test data, which is represented by the curve 72 that has been sucked out.

In view of the parallel anode scan data for the new photomultiplier tube represented by solid curve 73, the sensitivity of the arrangement in area "D" (see Figures 2 and 4a) is essentially lost. This low sensitivity is due to the "electron jumping" in the area between the first dynode 20 and the second dynode 22. As the corresponding electron trajectories 60 (see FIG. 2) show, part of the electron current emitted by the photocathode 16 is lost between the dynode 20 and the dynode 24 and does not hit the. Electron-emitting surface of the dynode 22 (this part of the electron current is not collected on the dynode 22). However, if the annulus 52 is replaced by a tapered U-shaped focusing ring 42 t, as shown in FIG. 5, then one reaches this way a noticeable improvement in sensitivity in the area '.' D ^rr - the curve. In the same way as described for the preferred curves in FIGS. 4 a and 4 b, a modified arrangement containing the tapered focusing ring 42 t (cf. a and 4 b are the resulting cathode

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- Ik -

Abtasbkurven 7 ^ι ί and 84, as well as the anode scanning curves 75 and 85 for the modified arrangement and clearly show the essential improvement of the sensitivity in the "D" area.

The tapered circular focus ring 42t shown in Fig. 5 was made in the same manner as the ring 42 (see Fig. 2). The previously presented data for the coordinate dimensions for the points b - b and b - b «(see FIG. 2) remained unchanged, as did the other important design values for the new device, which was described in detail in connection with FIG. The point br, however, was changed in order to obtain a desired symmetrical ring recess "J" of about 7 for the outer edge 4-3 ta, whereby the point hr , which is the coordinate point in relation to the zero point 0 (cf. Figure 2) set xrarde, was roughly equal to the coordinates (0, l40; 3> 602).

The combination of the new electron emittiex-endeii electrode described here and the beveled circular one Focusing ring 42 t not only leads to an essential Improving the uniformity of recording sensitivity, when the new electron-emitting surface of the device is scanned, it also becomes a remarkable one Improvement of the general properties, for example with regard to spatial uniformity the anode, the pulse height resolution and the plateau properties.

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In general, the first electron-emitting electrode (corresponding to the electrode 20 described here Electron discharge arrangement) have an electron-emitting material 56 a, which is used for the as an electron source or on the other hand as a photocathode (for example cesium antimony (Cs “Sb) photocathode) is suitable. The electrodes were then in from the photocathode surface Dependence of the focused, incident on the photocathode light generated; in this case, the previously described Photocathode l6 and the focusing electrode 42 (or 42 t) can be omitted, and a transparent one Grid is placed close to the electrode, around the emitted Catch electrons at the subsequent electrode.

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Claims (4)

- i6 - Protection claims / 1. / Electron discharge arrangement with at least two electron-optically aligned. Electrodes, "wherein at least a first electrode having an electron-emitting surface area and an anode are provided, and with devices to accelerate the electrons emitted from each of these surface areas in an electron stream which is passed in a non-repeating sequence from the first electrode to the subsequent, aligned electrodes and finally flows onto the anode for collection, characterized in that the surface area (56 a) of the first electrode (20) has a cross-sectional area with an essentially wavy curved line (L 2), which is joined by several adjacent arc areas (C ₁ - C ₂ , C ₂ - C, C ^ - C_) is formed. 2. Arrangement according to claim 1, characterized in that the first electrode in a transparent part (11) the wall (12) of the device is included and the surface area of the first electrode made of photo-emitting Material. 3. Arrangement according to claim 1, characterized in that the first electrode is included in a transparent part (11) of the casing (12) of the device, a semitransparent photocathode (l6) is attached to the inner surface of the transparent casing part and the acceleration devices an electrostatic focusing electrode (4t2, k2 t) arranged between the photocathode (16) and the first electrode, the focusing electrode (42, ^l k2 t ) consisting of a circular ring with a U-shaped 509823/0707 Cross-section and a central opening (54) as well as inner (42 b) and outer (42 a 4 42 ta) border parts. 4. Arrangement according to claim 3, characterized in that the outer border part (42 ta) "with respect to the
axial part of the focusing electrode (42 t) defines a symmetrical bevel of the border. 509823/0707 Λ * Blank page