EP0350111A1 - Sheet-type dynode, electron multiplier and photomultiplier having such dynodes - Google Patents

Abstract

Electron multiplier dynode (D), consisting of two parallel half-dynodes (d, d '), brought to the same electrical potential (V), and having the form of metal sheets (10,20) pierced with holes (11 , 21). According to the invention, the second half-dynode (d '), called the half-emitting dynode, is covered with a material (25) with secondary emission, the multiplication of the incident electrons (30) occurring on the surface (23) of said corresponding metal sheet (20), and in that said emitting half-dynode (d ') and the first half-dynode (d), called the extracting half-dynode, are offset between them. Application to photomultiplier tubes.

Description

The present invention relates to an electron multiplier dynode of the "leaf" type, that is to say essentially consisting of two half-dynodes in the form of sheets pierced with holes arranged in a network of a given pattern. It also relates to an electron multiplier and a photomultiplier tube comprising such multiplier dynodes.

The invention finds a particularly advantageous application in the field of photomultiplier tubes.

The use, in photomultiplier tubes, of dynodes and so-called "leaf" multipliers is known, for example, from French patent No. 2,549,288. This patent describes, in fact, an electron multiplier dynode, consisting of two parallel half-dynodes, brought to the same electrical potential, and produced using metal sheets pierced with holes regularly arranged in a repeating network of the same basic pattern. In a multiplier comprising several of these dynodes, the first half-dynode acts as an electrode for extracting the electrons from the previous dynode, while the second half-dynode is the electron-emitting electrode. For this purpose, the holes of the emitting half-dynode are given a largely flared shape so that the walls of the holes, covered with a secondary emission material, constitute the useful zones of electronic multiplication. The secondary electrons thus created, attracted by the following extracting electrode, cross the emitting half-dynode through the hole which gave birth to them. The advantages that a "leaf" multiplier brings to photomultiplier tubes are numerous. They offer in fact under a reduced bulk, a large collection surface, which makes them particularly advantageous when the incident electrons are in the form of a wide beam, as is the case with proximity focusing or in association with a first large focused dynode. On the other hand, the possibility of partitioning the multiplier makes it possible to produce, in the same tube, a certain number of secondary photomultiplier tubes, with the advantages that this provides in nuclear physics, for example, as regards the precise localization of the particles detected.

However, the electron multiplier dynodes known from the prior art have the drawback that the flared holes necessary for the multiplication of electrons are relatively expensive to produce since they require chemical attack and the use of masks. In addition, it should be noted that, in order to increase the multiplying surface, the outlet opening of the holes is relatively small, which makes it more difficult to correctly position the metal sheets relative to one another within a same electron multiplier.

Also, the technical problem to be solved by the object of the present invention is to produce an electron multiplier dynode, comprising a first half-dynode, called the extracting half-dynode, and a second half-dynode, called the transmitting half-dynode. , the half-dynodes being parallel, brought to the same electrical potential, and having the form of sheets pierced with holes arranged in a network of the same basic pattern, the second half-dynode having an electronic multiplication surface on which produces electron multiplication, a multiplying dynode which would be inexpensive to manufacture, and whose assembly would be facilitated by less severe tolerancing without harming collection efficiency.

The solution to the technical problem posed consists, according to the present invention, in that, said holes are holes with a straight edge, and in that the two half-dynodes are offset from each other so that each hole of one of the half-dynodes is located opposite the center of a basic pattern of the other half-dynode.

Thus, the holes being on a straight edge, since they are intended only for the passage of electrons, their production is much easier and less costly, and can be carried out using conventional mechanical means. On the other hand, the surface of electronic multiplication being appreciably larger than in the case of the dynodes of the state of the art, one can envisage increasing the diameter of the holes without much affecting the power of collection of the emitting half-dynodes , which has the effect of making the assembly of dynodes in an electron multiplier less critical. In this sense, an electron multiplier comprising, in order, a first emitting half-dynode and a plurality of electron multiplying dynodes, according to the invention, is remarkable in that each extracting half-dynode is located in position of coincidence with the preceding transmitting half-dynode, and in that the first transmitting half-dynode and the successive multiplying dynodes are brought to increasing electric potentials. Consequently, the extracting half-dynodes can play their role of extraction of the secondary electrons produced by the preceding half-emitting dynodes, without creating an obstacle to the passage of these electrons towards the following half-emitting dynodes, insofar as the holes of the extracting half-dynodes coincide with the holes of the preceding emitting half-dynodes.

Finally, a photomultiplier tube comprising a photocathode, a first dynode, an electron multiplier according to the invention, coupled to the first dynode, and an anode, is remarkable in that, between said first dynode and the multiplier, is interposed a input gate, parallel to the first emitting half-dynode, and whose electrical potential is equal to the electrical potential of said first emitting half-dynode.

As will be seen below in detail, the grid input serves as a shielding electrode essential to the first emitting half-dynode so that the electrons which come from it can be extracted by the extracting half-dynode of the following dynode.

• La figure 1 est une vue en coupe d'une dynode mul­tiplicatrice d'électrons selon l'invention.
• La figure 2 est une vue de dessus de la dynode de la figure 1.
• La figure 3 est une vue en coupe d'un multiplica­teur d'électrons selon l'invention.
• La figure 4 est une vue en coupe d'un tube photo­multiplicateur selon l'invention.

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 electron multiplier dynode according to the invention.
• Figure 2 is a top view of the dynode of Figure 1.
• Figure 3 is a sectional view of an electron multiplier according to the invention.
• Figure 4 is a sectional view of a photomultiplier tube according to the invention.

FIG. 1 shows, in section, an electron multiplier dynode D, consisting of two half-dynodes d, d ′ parallel and brought to the same electrical potential V. These half-dynodes are in the form of metal sheets 10, 20, made for example from mild steel, and pierced with holes 11, 21 arranged in a regular repeating network of the same basic pattern 12, 22. In the embodiment shown in FIG. 2, the basic patterns 12, 22 are both constituted by an equilateral triangle, but they could just as easily be constituted by a square, a rectangle, etc. As can be see in Figures 1 and 2, the holes 11, 21 are holes with a straight edge, very simple to make. Typically, said holes 11, 21 can have a diameter of 0.5 mm, while the distance between two consecutive holes is of the order of 1 mm. On the other hand, the second half-dynode d ′, called the half-emitting dynode is covered with a material 25 with secondary emission, such as antimony or beryllium oxide, the multiplication of incident electrons 30 occurring on the surface 23 of said corresponding metal sheet 20, the second dynode d ′ can also be made of a material giving rise to secondary emission such as a copper-beryllium alloy having undergone the conventional treatment: heating-migration of beryllium and oxidation. Finally, FIGS. 1 and 2 show that the emitting half-dynode d ′ and the first half-dynode d, known as the extracting half-dynode, are offset between them so that each hole 11, 21 of one d, d ′ half dynodes is located opposite the center 24, 14 of a basic pattern 22, 12 of the other d ′, d half dynode. In this way, the electrons 30 which pass through the extractor half-dynode d through a hole 11 necessarily meet the emitting half-dynode 20 at a location endowed with secondary emission.

The electron multiplier 50 shown in FIG. 3 comprises, in order, a first emitting half-dynode d′₂ and a plurality of dynodes D₃ ..., D _i , D _{i + 1} , ..., D _n electron multipliers, of the type described above with reference to FIGS. 1 and 2. As shown in FIG. 3, each extracting half-dynode d _{i + 1} is located in the position of coincidence with the emitting half-dynode d ′ _I previous. Furthermore, so that the electrons can progress from the first emitting half-dynode d d to the last emitting half-dynode d′n, the first emitting half-dynode dode and the d₃ dynodes, ... , D _i , D _{i + 1} , ..., D _n successive multipliers are brought to electric potentials V₂, V₃, ..., V _i , V _{i + 1} , ..., V _n increasing. The extracting half-dynode d _{i + 1} , for example, therefore has the function of attracting towards the half-emitting dynode of ′ _{i + 1} the electrons coming from the half-emitting dynode of ′ _i , but it also serves to shield electrically the half-dynode emitting _{i + 1} of the preceding dynodes. In the absence of this shielding, which creates a weak field between the half-dynodes d _{i + 1} and d ′ _{i + 1} , it would not be possible for the electrons emitted by the half-dynode emitting d ′ _{i + 1} to be extracted by the following extracting half-dynode d _{i + 2} . In order for the shielding effect to be sufficient, it is advantageous for the distance between an extracting half-dynode and the emitting half-dynode of the same dynode is relatively large, for example from 0.5 to 0.8 mm. The distance between a transmitting half-dynode and the following extracting half-dynode can be smaller, of the order of a few tenths of a mm, typically 0.3 mm.

FIG. 4 shows, in section, a photomultiplier tube 60 comprising a photocathode 61, a first large cylindrical d₁ D₁, a multiplier 50 conforming to that of FIG. 3, and an anode A. By way of example, the multiplier 50 of electrons is coupled to the first dynode Dode using the coupling means described in the French patent application, unpublished, No. 88 07 778, but, of course, other coupling means known to the skilled in the art can be used. As can be seen in Figure 4, is interposed between the first dynode D₁ and the multiplier 50, an input gate G, parallel to the first half-dynode emitting d′₂, and whose electrical potential is equal to the potential electric V₂ of said first emitting half-dynode ₂. Said input gate G therefore constitutes, with the first emitting half-dynode, a second dynode D₂ equivalent to higher order dynode waters D₃, ..., D _n . The essential role of the input gate G is to ensure, with good transparency, a shielding for the first half-dynode emitting ₂. Usually, the electrical potential V₁ of the first dynode D₁ is less than the electrical potential V₂ of the equivalent dynode D₂.

Claims (3)

1. Electron multiplier dynode (D), comprising a first half-dynode (d), called the extracting half-dynode, and a second half-dynode (d ′), called the transmitting half-dynode, the half-dynodes (d , d ′) being parallel, brought to the same electrical potential (V), and having the form of sheets (10,20) pierced with holes (11,21) arranged in a network of the same pattern (12,22) base, the second half-dynode (d ′) having an electronic multiplication surface on which the multiplication of electrons occurs, characterized in that, said holes (11,21) are holes with a straight edge, and in that that the two half-dynodes are offset from each other so that each hole (11,21) of one (d, d ′) of the half-dynodes is opposite the center (24,14) of a pattern ( 22,12) base of the other (d ′, d) half-dynode. 2. Multiplier (50) of electrons comprising, in order, a first emitting half-dynode (d′₂) and a plurality of dynodes (D₃, ..., D _i , D _{i + 1} , ... , D _n ) electron multiplier, according to claim 1, characterized in that each extracting half-dynode (d _{i + 1} ) is situated in position of coincidence with the preceding half-emitting dynode (d ′ _i ), and in that the first emitting half-dynode (d′₂) and the successive multiplier dynodes (D₃, ..., D _i , D _{i + 1} , ..., D _n ) are brought to electric potentials (V₂, V₃ , ..., V _i , V _{i + 1} , V _n ) increasing. 3. Photomultiplier tube (60) comprising a photocathode (61), a first dynode (D₁), an electron multiplier (50) according to claim 2, coupled to the first dynode (D₁), and an anode (A), characterized in that, between said first dynode (D₁) and the multiplier (50), an input grid (G) is interposed, parallel to the first emitting half-dynode (d′₂), and whose electrical potential is equal to the electrical potential (V₂) of said first emitting half-dynode.

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