EP0131339A1 - Electron multiplier element, electron multiplying device made up of this element and its application to a photomultiplier tube - Google Patents

Abstract

Multiplier element (11) of secondary emission electrons of the "plate with holes" type, characterized in that it is composed, on the one hand, of a first plate (12) pierced with holes (13), called holes multipliers, each multiplier hole (13) defining, on a first face (14) of said first plate (12), an opening (15), said entry opening, larger than the opening (16), said opening outlet, defined on the second face (17) of the first plate (12), and, on the other hand, of a second plate (22), parallel to the first plate (12), also pierced with holes (23) , said auxiliary holes, the opening (25) of which on a first face (24) of the second plate (22), situated opposite the second face (17) of the first plate (12), is substantially equal to l opening (16) for exit from the multiplier holes (13) and smaller than the opening (26) for said auxiliary holes (23) defined on the second face (27) of the second plate (22), and what, l Said first (12) and second (22) plates are electrically isolated from each other, the second plate (22) being brought to a potential (VI) greater than the potential (Vo) of the first plate (12). Application to photomultiplier tubes.

Description

The present invention relates to an electron multiplier element with secondary emission of the "hole plate" type. It also relates to an electron multiplier device comprising a parallel stack of N electron multiplier elements with secondary emission according to the invention, and an application of this multiplier device to a photomultiplier tube.

An electron multiplier device in accordance with the preamble is known, for example, from French patent No. 2 299 722. This patent describes an electron multiplier device constituted by a stack of electron multiplier elements with secondary emission electrons composed of two half-plates pierced with holes with concave walls so that, the half-plates being brought together, the corresponding holes of each half-plate form a single barrel-shaped hole. The walls of these holes carry a layer of a secondary emission material, the useful part of each single hole being constituted by the lower half-hole.

The advantage of such a structure of electron multiplier elements is that it allows, under a reduced bulk, the multiplication of incident electrons appearing, at the level of the plate, in the form of a wide beam, for example a cylindrical beam, and this without the need to use electronic focusing optics. On the other hand, a repetitive structure of low pitch lends itself well to the formation of intensified images.

However, this type of electron multiplier element has a drawback which lies in the fact that a certain number of incident electrons do not give rise to secondary emission because they pass directly through the multiplier holes without undergoing multiplication and than others reach the multiplier in places from which the secondary electrons cannot be extracted, for example between two holes or outside the useful part of the holes.

The object of the present invention is to remedy this drawback by seeking to increase the collection efficiency of the multiplier elements.

Indeed, according to the present invention, an electron multiplier element with secondary emission of the "plate with holes" type is notably remarkable in that it is composed, on the one hand, of a first plate pierced with holes, called multiplier holes, arranged in a regular plane network, each multiplier hole defining, on a first face of said first plate, an opening, called inlet opening, larger than the opening, called outlet opening, defined on the second face of the first plate, the inlet opening of each multiplier hole being substantially tangent to the inlet openings of the closest neighbors of said multiplier hole, and, on the other hand, of a second plate, parallel to the first plate, also pierced with holes, called auxiliary holes, the opening of which on a first face of the second plate, located opposite the second face of the first plate, is substantially equal to the outlet opening of the multiplicative holes eurs and smaller than the opening of said auxiliary holes defined on the second face of the second plate, and in that, said first and second plates are electrically isolated from each other, the second plate being brought to a potential greater than the potential of the first plate. Thus, because the inlet openings are almost tangent and the multiplier holes have an open structure in a half barrel, the first plate offers the incident electrons a much larger useful multiplication surface than in the plates with known holes. The second plate, the holes of which, called auxiliary, substantially reproduce the shape of the outlet opening multiplier holes, serves as an accelerating electrode.

The inlet and outlet openings of the multiplier holes may be circular, and the holes assembled in a regular square or hexagonal plane network, the latter configuration having the advantage of increasing the useful multiplication surface of the first plate. In order to further increase the useful multiplication surface, it is envisaged that the entry opening of the multiplier holes of the first plate is substantially square or hexagonal, and in that said regular plane network is square or respectively hexagonal.

It is also provided that the outlet openings of the multiplier holes of the first plate are offset with respect to their inlet openings so that said multiplier holes are asymmetrical. The advantage of having asymmetrical multiplier holes is to spatially define the position of the useful multiplication part with respect to the exit opening of the multiplier holes and therefore to preferentially orient the trajectories of the secondary electrons.

The multiplier element according to the invention can be advantageously used to produce a high efficiency collection electron multiplier device. Indeed, in accordance with the present invention, an electron multiplier device comprising a parallel stack of N electron multiplier elements with secondary emission according to the invention is particularly remarkable in that the distance between the second face of the second plate of the i ^th multiplier element and the first face of the first plate of the (i + l) ^th multiplier element is greater than the distance separating the first and second plates of the same multiplier element, and in that the second plate of the i ^th multiplier element is at an electric potential identical to the electric potential of the first plate of the (i + l) th multiplier element. This configuration, in which the multiplier elements are relatively far apart, has the advantage of a better collection of electrons between one multiplier and the next.

A particular embodiment of the multiplier device according to the invention consists in that the multiplier and auxiliary holes of the (i + 1) ^th multiplier element are located opposite the multiplier and auxiliary holes of the ith multiplier element, so that the multiplier holes and auxiliary counterparts of the N multiplying elements constitute rectilinear channels whose direction is perpendicular to the faces of the N multiplying elements. This embodiment has the advantage of allowing the formation of intensified images, when it is used in a tube of the image intensifier type, since the secondary electrons leaving a channel of the device come in principle only from the multiplication of incident electrons entering the same channel.

On the other hand, if it is desired to further increase the gain of the device according to the invention, but by renouncing the possibility of image formation when the multiplier holes are symmetrical, provision is made for the multiplier and auxiliary holes of the (i + 1 ) ^th multiplier element are offset with respect to the multiplier and auxiliary holes of the th multiplier element so that the homologous multiplier and auxiliary holes of the N multiplier elements constitute rectilinear channels whose direction makes a., acute angle with the normal to the faces of the N multiplier elements. In particular, a staggered structure of the multiplier holes ensures very good efficiency of the whole of the multiplier device according to the invention. Note that a device of multiplier elements with asymmetrical holes allows both good electronic performance and the possibility of image formation. In order to avoid the return of ions and light to the photocathode through said straight channels, when the device according to the invention is incorporated into a photomultiplier tube, it is envisaged that the multiplier and auxiliary holes of the (i + ₁ ) ^th multiplier element are offset with respect to the multiplier and auxiliary holes of the i ^th multiplier element so that the homologous multiplier and secondary holes of the N multiplier elements constitute channels describing a propeller.

The electron multiplier device according to the invention applies in a particularly advantageous manner to a photomultiplier tube comprising a photocathode and at least one anode. In this application, said multiplier device is placed between the photocathode and the anode, and at least partially replaces the conventional dynodes. This type of photomultiplier tube has many advantages: large collection surface, good linearity, speed and small footprint.

A particular application of the multiplier device according to the invention to a photomultiplier tube is notably remarkable in that, the photomultiplier tube comprising n adjacent anodes, said multiplier device is placed near the photocathode and is divided into n secondary multiplier devices by partitions electron-tight and located opposite the separation zones of two consecutive anodes so as to produce n secondary photomultiplier tubes in the same photomultiplier tube. Thus, each secondary photomultiplier supplies an electrical signal proportional to the light information received by the corresponding photocathode element. This kind of tube is well suited for the localization of nuclear particles, for example.

The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be implemented.

• Figure 1 is a sectional view of an embodiment of the multiplier element according to the invention.
• Figure 2 is a top view of the first multiplier element plate of figure 1.
• Figure 3 is a top view of a first variant of a first plate of the multiplier according to the invention.
• Figure 4 is a top view of a second variant of a first plate of the multiplier according to the invention.
• Figure 5 is a top view of a third variant of a first plate of the multiplier according to the invention.
• FIG. 6 is a section along line II-II of the multiplier element of FIG. 4 or III-III of FIG. 5.
• FIG. 7 is a section through a multiplier device according to the invention constituted by multiplier elements similar to that of FIG. 1.
• FIG. 8 is a section through an alternative embodiment of the multiplier device of FIG. 7.
• FIG. 9 is a section through a multiplier device according to the invention constituted by multiplier elements similar to that of FIG. 6.
• FIG. 10 is a section through a variant of the multiplier device of FIG. 9.
• FIG. 11 a is a diagram giving the principle of embodiment of a multiplier device according to the invention, the multiplier elements of which are assembled in a helix.
• Figure 11b shows a multiplier element in a form suitable for implementing the principle of embodiment illustrated in Figure 11a.
• FIG. 12 is a section through a photomultiplier tube comprising a multiplier device according to the invention.
• FIG. 13 is a section through a photomultiplier tube constituted by secondary photomultipliers produced using a multiplier device according to the intention.

Figure 1 shows, in section, a multiplica element 11 electron emitter with secondary emission of the "hole plate" type. As shown in FIG. 1, this multiplier element is composed, on the one hand, of a first plate 12 pierced with holes 13, called multiplier holes, arranged in a regular plane network. Each multiplier hole 13 defines, on a first face 14 of said first plate, an opening 15, called the inlet opening, larger than the opening 16, called the outlet opening, defined on the second face 17 of the first plate 12 , the inlet opening of each multiplier hole being substantially tangent to the inlet openings of the nearest neighbors of said multiplier hole. On the other hand, the multiplier element 11 comprises a second plate 22 parallel to the first plate 12, also pierced with holes 23, called auxiliary holes, the opening 25 of which on a first face 24 of the second plate 22, located in look of the second face 17 of the first plate 12, is substantially equal to the opening 16 for output of the multiplier holes 13 and smaller than the opening 26 of said auxiliary holes 23 defined on the second face 27 of the second plate 22. As can be seen in FIG. 1, said first 12 and second 22 plates are electrically isolated from each other, the second plate 22 being brought to a potential V1 greater than the potential Vo of the first plate 12.

At least the first plate 12 is produced in a material which can give rise to secondary emission such as a copper-beryllium alloy having undergone the conventional treatment: heating-migration of beryllium and oxidation. It can also be produced in an inexpensive material, such as mild steel, covered with secondary emission material: layer of oxidized copper-beryllium alloy or layer of manganese oxide. Compared to known electron multipliers, of the known "hole plate" type, the multiplier element 11 according to the invention offers incident electrons 60 on the side of the first face 14 of the first plate 12 a collection and multiplication surface. significantly larger. The electrical insulation of the two plates 12 and 22 can be done, for example, using small glass beads 70, 100 to 200 μm in diameter sealed at the periphery of said plates. The second plate 22, whose potential is greater than that of the first plate 12, acts as an accelerating electrode.

Figure 2 shows a top view of the first plate 12 of the multiplier 11 of Figure 1. According to Figure 2, the inlet 15 and outlet 16 openings of the multiplier holes 13 are circular and said regular flat network is square. FIG. 3 gives a first variant of the plate shown in FIG. 2 which makes it possible to increase the useful multiplication surface of the first plate. According to FIG. 3, the inlet 15 and outlet 16 openings of the multiplier holes 13 of the first plate 12 are circular and said regular plane network is hexagonal.

If one wishes to further increase the collection and multiplication efficiency of the first plate, one can refer to FIGS. 4 and 5 in which the inlet opening 15 of the multiplier holes 13 of the first plate 12 is substantially square , respectively hexagonal, and said regular plane network is square, respectively hexagonal.

FIGS. 5 and 6 show a third variant of a multiplier element according to the invention in which the outlet openings 16 of the multiplier holes 13 of the first plate 12 are offset with respect to their inlet openings 15 so that said holes multipliers 13 are asymmetrical. The realization of such multiplier elements is done by chemical attack on both sides of a metal plate through masks offset appropriately.

FIG. 7 shows in section an electron multiplier device comprising a parallel stack of N (icd. = 3) multiplier elements similar to that represented in FIG. 1. As can be observed in FIG. 7, the distance D between the second face 27 of the second plate 22 of the i ^th multiplier element and the first face 14 of the first plate 12 of the (i + 1) th multiplier element is greater than the distance d separating the first 12 and second 22 plates of the same multiplier element. On the other hand, the second plate 22 of the i ^th multiplier element is at an electric potential Vli identical to the electric potential Vo (i + l) of the first plate 12 of the (i + 1) ^th multiplier element. The multiplier device according to the invention has better collection efficiency than in the known devices, due to the good collection efficiency of each multiplier element and also the effect of distance between two consecutive multiplier elements.

The multiplier elements are kept at distance D from each other by spacers 29 arranged at the periphery of the plates.

In the embodiment shown in FIG. 7, the multiplier holes 13 and auxiliary ₂₃ of the (i + 1) th multiplier element are located opposite the multiplier and auxiliary holes of the i ^th multiplier element, so that the multiplier and auxiliary holes counterparts of the N multiplying elements constitute rectilinear channels whose direction 30 is perpendicular to the faces of the N multiplying elements. This embodiment of the multiplier device according to the invention offers the advantage of being able to be used in a tube of the image intensifier type since the secondary electrons leaving a channel of the device result from the multiplication of incident electrons 60 entering the same channel.

Figure 8 shows in section an alternative embodiment of the multiplier device of Figure 7, variant in which the multiplier holes 13 and auxiliary 23 of the (i + 1) ^th multiplier element are offset relative to the multiplier holes and auxiliary of the i ^th element multiplier so the multiplier holes and auxiliary counterparts of the N multiplying elements constitute rectilinear channels whose direction 31 makes an acute angle with the normal 30 to the faces of the N multiplying elements. This variant makes it possible to increase the gain of the multiplier device according to the invention since incident electrons which would pass through a multiplier element at the center of a multiplier hole, therefore without multiplication, are then multiplied by the following multiplier element whereas 'they would not be in the embodiment of Figure 7. By cons, as shown in Figure 8, the device shown can not be used for image formation because there is no one-to-one correspondence between a given multiplier of the hole 1 ^th multiplier element and a multiplier hole ^leme _N and last multiplying element.

However, both good electronic efficiency and the possibility of image formation can be obtained by using multiplier elements with asymmetric multiplier holes as shown in FIG. 6. This is the case of the multiplier device shown in FIG. 9. In order to avoid the offset between the input image and the output image, which offset can be significant if the number N of multiplying elements is large, it is provided, as shown in FIG. 10, that the holes asymmetric multiplier 13 of the (i + 1) ^th multiplier element are in anti-parallel configuration with respect to the asymmetrical _multiplier holes of the i ^th multiplier element.

In order to prevent ions or light from going up towards the photocathode by said rectilinear channels in the case where the device according to the invention forms part of a photomultiplier tube, provision is made, with reference to FIG. multiplier holes 13 and auxiliaries 23 of the (i + 1) ^th multiplier element are offset with respect to the multiplier holes and auxiliaries of the th multiplier element so that the homologous multiplier and secondary holes of the N multiplier elements constitute channels describing a helix.

The axes (x, y) of the N multiplying elements remain parallel to each other, but the centers 70 of the reference multiplier holes 23 are regularly distributed over a given circle 71. The centers 70 of two consecutive holes 23 make with the center 72 of the circle 71 a given angle which depends on the total number N of multiplying elements. FIG. 11b shows a top view of a plate of a triangle-shaped multiplier element, the useful part of which is represented by the circle 80. This plate has a tab 81 for electrical connection and is pierced with three holes 82 which allow the 'assembly of the plates of the multiplying elements using small columns passing through the holes 82. The helical offset is obtained by shifting the position of the three holes 82 in opposite directions after having determined the origins of the axes (x, y) by fixing pins which penetrate into multiplier or auxiliary holes in the central area 80.

The electron multiplier device according to the invention finds a particularly advantageous application to photomultiplier tubes. As shown in FIG. 12, the photomultiplier tube comprises a photocathode 41 and an anode 42; the multiplier device 40 according to the invention is placed between the photocathode 41 and the anode 42, the inlet opening 15 of the multiplier holes being oriented towards the photocathode 41. In the example of FIG. 12, the tube has a first dynode 43 which can be of large size, hence greater collection efficiency as well as better linearity, better speed and less bulk.

FIG. 13 shows, in section, another application of the invention to a photomultiplier tube comprising n adjacent anodes 42. In this application, said multiplier device is placed near the photocathode 41 and is divided into n secondary multiplier devices by partitions 50 which are sealed against electrons and situated opposite the zones 51 of separation of two consecutive anodes 42 so as to produce n tubes photomultipliers secondary in the same photomultiplier tube. Tubes of the type shown in FIG. 13 find advantageous use in nuclear physics because they allow precise localization of the particles detected.

The watertight partitions 50 can be produced in a conventional manner by masking and photoengraving of a metal plate.

Claims (13)

1. Multiplier element (11) of secondary emission electrons of the "hole plate" type, characterized in that it is composed, on the one hand, of a first plate (12) pierced with holes (13), said multiplier holes, arranged in a regular planar network, each multiplier hole (13) defining, on a first face (14) of said first plate (12), an opening (15), called entry opening, larger than the opening (16), called the outlet opening, defined on the second face (17) of the first plate (12), the inlet opening (15) of each multiplier hole being substantially tangent to the more close neighbors of said multiplier hole, and, on the other hand, of a second plate (22), parallel to the first plate (12), also pierced with holes (23), called auxiliary holes, the opening (25) on a first face (24) of the second plate (22), located opposite the second face (17) of the first plate (12), is substantially equal to the opening (16) for the exit from the multiplier holes (13) and smaller than the opening (26) for said auxiliary holes (23) defined on the second face (27) of the second plate (22), and in that , said first (12) and second (22) plates are electrically isolated from each other, the second plate (22) being brought to a potential (VI) greater than the potential (Vo) of the first plate (12) . 2. Multiplier element according to claim 1, characterized in that the inlet (15) and outlet (16) openings of the multiplier holes (13) are circular and in that said regular plane network is square. 3. Multiplier element according to claim 1, characterized in that the inlet (15) and outlet (16) openings of the multiplier holes (13) of the first plate (12) are circular and in that said regular flat network is hexagonal. 4. Multiplier element according to claim 1, characterized in that the inlet opening (15) of the holes multipliers (13) of the first plate (12) is substantially square, and in that said regular plane network is square. 5. Multiplier element according to claim 1, characterized in that the inlet opening (15) of the multiplier holes (13) of the first plate (12) is substantially hexagonal, and in that said regular plane network is hexagonal. 6. Multiplier element according to claim 1, characterized in that the outlet openings (16) of the multiplier holes (13) of the first plate ( ¹ 2) are offset relative to their inlet openings (15) so that said multiplier holes (13) are asymmetrical. 7. electron multiplier device comprising a parallel stack of N electron multiplier elements with secondary emission according to one of claims 1 to 6, characterized in that the distance (D) between the second face (27) of the second plate (22) of the i ^th multiplier element and the first face (14) of the first plate (12) of the (i + 1) ^th multiplier element is greater than the distance (d) separating the first (12) and second ( 22) plates of the same multiplier element, and in that the second plate (22) of the i ^th multiplier element is at an electric potential (Vli) identical to the electric potential (Vo (i + 1)) of the first plate ( 12) of the (i + 1) ^th multiplier element. 8. electron multiplier device according to claim 7, characterized in that the multiplier holes (13) and auxilliary (23) of the (i + 1) ^th multiplier element are located opposite the multiplier and auxiliary holes of the i ^th multiplier element , so that the homologous multiplier and auxiliary holes of the N multiplier elements constitute rectilinear channels whose direction (30) is perpendicular to the faces of the N multiplier elements. 9. electron multiplier device according to claim 7, characterized in that the multipli cators (13) and auxiliaries (23) of the (i + 1) ^th multiplier element are offset with respect to the multiplier holes and auxiliaries of the i ^th multiplier element so that the homologous multiplier holes and auxiliaries of the N multiplier elements constitute rectilinear channels of which the direction (31) makes an acute angle with the normal (30) to the faces of the N multiplying elements. 10. electron multiplier device according to claim 7, characterized in that the multiplier holes (13) and auxilliary (23) of the (i + 1) ^th multiplier element are offset with respect to the multiplier holes and auxilliary of the i ^th multiplier element so that the homologous multiplier and secondary holes of the N multiplier elements constitute channels describing a helix. 11. Electron multiplier device according to claim 6 and one of claims 7 to 10, characterized in that the asymmetric multiplier holes (13) of the (i + 1) ^th multiplier element are in head-to-tail configuration relative to the multipliers dissymétri- q _ues of the i ^th multiplier element holes. 12. Application of the electron multiplier device according to one of claims 7 to 10 to a photomultiplier tube comprising a photocathode (41) and at least one anode (42), characterized in that said multiplier device is placed between the photocathode ' (41) and the anode (42), the inlet opening (15) of the multiplier holes (13) being oriented towards the photocathode (41). 13. Application according to claim 12, characterized in that, the photomultiplier tube comprising n adjacent anodes (42), said multiplier device is placed near the photocathode (41) and is divided into n secondary multiplier devices by partitions (50 ) electron-tight and located opposite the zones (51) of separation of two consecutive anodes (42) so as to produce n secondary photomultiplier tubes in the same photomultiplier tube.

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