FR2504728A1 - Electron multiplier for photomultiplier tube - has electron deflecting grid assembly having elements repeated at same or sub-multiple of dynode structure spacing - Google Patents

Abstract

The device has an electrode (11) held at a given potential formed by a number of spaced electron multiplier elements (13) arranged in a repetitive venetian blind structure extending along a given direction (15). The multiplier also has an electron deflection grid (12) defined by a number of deflection elements (16) which are spaced from one another along a parallel direction (17) to the multiplier elements (13). The spacings between the deflection elements (16) is the same as that of the multiplier elements (13) or a sub-multiple of it. Pref. the grid (12) is held at a lower potential than the electrode potential.

Description

"MULTIPLICATOR DEVICE BY ELEClRON AND APPLICATION TO PHOTOMULllPLICATORS"
The present invention relates to an electron multiplier device by secondary emission, comprising in particular a first multiplier electrode constituted by a set of electron multiplier elements spatially distributed, at least in one direction, called the main direction, in a repetitive structure of steps. given, said first electrode being brought to a given electrical potential. It also relates to an application of the electron multiplier device according to the invention to the production of a photomultiplier tube.

 In the remainder of this specification, the term “electron multiplier element” means any zone of the first electrode, coated with a material with secondary emission and the vast majority of the secondary electrons emitted of which is collected by a second electrode placed in the vicinity of the first electrode.

 An electron multiplier device in accordance with the preamble is known, for example, from French patent n 2 299 722. This patent describes an electron multiplier by secondary emission constituted by a metal plate, called "channel plate", in which Multiplier elements are formed by channels formed through channels across the entire thickness of the plate, the walls of these channels carrying a layer of secondary emission material. The advantage of such an electron multiplier structure is that '' it allows, under a small footprint, 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 it being necessary to use an optic focusing electronics. 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 has a drawback which resides in the fact that a certain number of incident electrons do not give rise to secondary emission, namely that they pass directly through said first electrode without encountering any elements. multipliers, that is to say they reach the first electrode in places where the secondary electrons can not extract other, for example between two channels of a "channel plate".

 The object of the present invention is to remedy this drawback. It is based on the idea that the collection efficiency of the first electrode could be increased by modifying the trajectories of the incident electrons so that they concentrate preferentially at the level of the electron multiplier elements.

 Indeed, according to the present invention, an electron multiplier device by secondary emission, comprising in particular a first multiplier electrode constituted by a set of electron multiplier elements spatially distributed, at least in one direction, called main direction, in one repetitive structure of given pitch, said first electrode being brought to a given electrical potential, is notably remarkable in that it also comprises at least one electron deflector grid constituted by a set of spatially distributed deflector elements, at least in a direction, called the main grid direction, in a repetitive structure of given pitch, said grid pitch, and in that the main grid direction is substantially parallel to the main direction of the first electrode, the grid pitch being equal to the pitch of the first electrode or a submultiple of this pitch, and in that said deflecting grid is brought to a other given electrical potential, called grid potential.

 Thus, before reaching the first electrode, the incident electrons are deflected by the deflecting grid so that the beam, initially substantially homogeneous, formed by these incident electrons, is transformed into a plurality of secondary beams after passage of the grid. As will be seen further on in embodiments of the invention, it is possible, in addition, on the one hand, the position of the grid relative to the first electrode and, on the other hand, the grid potential by compared to the potential of the first electrode, to make the secondary beams converge to a large extent on the electron multiplier elements and thus to increase very significantly the collection efficiency of the first electrode.

 In a preferred embodiment of the invention, the gate potential is lower than the potential of the first electrode, in order to prevent the incident electrons from being picked up by the gate.

 In a first embodiment of an electron multiplier device according to the invention, the first multiplier electrode of which is constituted by a set of electron multiplier elements having the form of flat, parallel metallic lamellae deducing one on the other by a first translation whose direction and modulus correspond respectively to the main direction and to the pitch of the first electrode, it is provided that all of the deflector elements is constituted by a network of metal blades, parallel and perpendicular to the main direction of the first electrode, deducing from each other by a second translation, the direction and modulus of which correspond respectively to the main grid direction and to the grid pitch.

 In a second embodiment of an electron multiplier device according to the invention, the first multiplier electrode of which is made up of a set of electron multiplier elements in the form of metallic lamellae of revolution around a same axis of revolution, the main direction of the first electrode being defined by any direction perpendicular to and passing through the axis of revolution, and the distance separating, in this direction, two consecutive metallic lamellae of revolution being defined as the pitch of the first electrode, it is envisaged that the set of deflector elements is made up, in a plane perpendicular to the axis of revolution, by metal wires arranged in concentric circles whose common center is located on said axis of revolution, the main direction of grid being defined by the direction of any diameter common to said concentric circles, and the distance between two concentric circles consecutive risks being equal to the grid pitch.

In a third embodiment of an electron multiplier device according to the invention, the first electrode of which is of the "channel plate" type, said channels passing through said plate over its entire thickness at locations forming a two-dimensional network in which said main direction of given pitch is constituted by a first direction and a second direction forming between them an angle A, it is provided that the set of deflector elements is constituted by two networks, called first and second network, of parallel metallic wires and coplanar, the metal wires of each of the networks deducing from each other by a translation whose direction and modulus correspond respectively to said main grid direction and to said grid pitch, and in that the main grid direction of the first network makes the angle
A with the main grid direction of the second network.

 In a fourth embodiment of an electron multiplier device according to the invention, the first electrode of which is of the “channel plate type, said channels passing through said plate over its entire thickness at locations forming a two-dimensional network in which said- main direction of given pitch is constituted by a first direction and a second direction making between them an angle of 600, it is expected that the set of deflector elements is constituted by metallic wires forming a plurality of hexagons having a center of symmetry located on the axis of the channels, the directions of the sides of said hexagons being coincident with the directions of the perpendicular bisectors of the segments joining two consecutive centers of symmetry, while two opposite vertices of each hexagon are connected by a metal wire, and in that said hexagons form a two-dimensional network in which said main direction of given pitch grid is constituted by the first direction and the second direction of the first electrode, the grid pitch being equal to the pitch of the first electrode.

 Finally, the electron multiplier device according to the invention is, in general, intended to equip any intensification system with an electron beam, and in particular photomultiplier tubes. Indeed, an application of the electron multiplier device according to the invention to the production of a photomultiplier tube is mainly remarkable in that, said first multiplier electrode constituting the first dynode of the photomultiplier tube, said deflector grid is located between this first dynode and photocathode of the photomultiplier tube. The higher order dynodes will preferably, but without this being necessary, have a repetitive structure similar to that of the first dynode. The photomultiplier tubes thus provided with the electron multiplier device according to the present invention, at the level of the first dynode, improved collection efficiency and lower dispersion of the transit time between the first and second dynodes.

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

 Figure 1 is a perspective view of a first embodiment of the electron multiplier device according to the invention.

 Figure 2 is a sectional view along line II-II of the electron multiplier device of Figure 1.

 Figure 3 is a top view of a second embodiment of the electron multiplier device according to the inventi-on.

 FIG. 4 is a sectional view along line III-III of the electron multiplier device of FIG. 3.

 Figure 5 is a top view of a third embodiment of an electron multiplier device according to the invention.

 FIG. 6 is a sectional view along line IV-IV of the electron multiplier device of FIG. 5.

 Figure 7 is a top view of a fourth embodiment of the electron multiplier device according to the invention.

 FIG. 8 is a sectional view along line V-V of the electron multiplier device of FIG. 7.

 Figure 9 is a sectional view of a photomultiplier tube equipped with an electron multiplier device according to the invention.

Figure 1 shows, in perspective, and Figure 2, in section along the line II-II of Figure 1, a first embodiment of an electron multiplier device according to the invention. This device comprises a first multiplier electrode 11 constituted by a set of electron multiplier elements which, in the embodiment shown in FIGS. I and 2, are flat, parallel metallic strips 13 and carrying on their face 14 a layer of a secondary emission material. These lamellae 13 are spatially distributed, in the direction represented by line 15, called the main direction, in a repetitive structure of given pitch, in which the lamellae 13 are deduced from each other. by a first translation, the direction and module of which correspond respectively to the main direction 15 and to step 1 of the first electrode II
This first electrode is brought to a given electrical potential e. The electron multiplier device shown in FIGS. 1 and 2 further comprises a deflector grid 12 of electrons formed by a set of deflector elements formed by a network of metal blades 16, parallel and perpendicular to the main direction 15 of the first These metal blades 16 are spatially distributed, in the direction 17 of the line 11-11, called the main grid direction in a repetitive structure of given pitch Pg1, said grid step, in which the metal blades 1 are deduced from the one from the other by a second translation, the direction and modulus of which correspond respectively to the main grid direction 17 and to the grid pitch Pg1, the main grid direction 17 being substantially parallel to the main direction 15 of the first electrode and the grid pitch Pg1 being equal to the pitch of the first electrode. The deflecting grid 12 is brought to another electrical potential Vg, called the potential of g rille, which, in a preferred embodiment of the invention, is less than the potential Va of the first electrode 11. FIG. 2 shows the effect of the repulsive potential of the grid on the trajectory 18 of those of the incident electrons which, in the absence of a grid, would pass directly through the first electrode without secondary multiplication.

By way of example, the Applicant has studied an electron multiplier device in accordance with the invention in which the grid 12 is located 0.8 mm from the first electrode 11, the electrical potentials Va and
Vg being respectively equal to 200 V and 50 V.

 In the exemplary embodiment shown in FIGS. 1 and 2, the metal blades 1o of the grid 12 have been placed directly above the edges 19 of the strips 13.

It is understood that, taking into account the geometry of the lamellae and the potentials applied, the grid 12 can be translated in its plane so as to optimize the collection efficiency of the first electrode 11.

 FIGS. 3 and 4 show a second embodiment of an electron multiplier device according to the invention, comprising a first multiplier electrode 21 constituted by a set of electron multiplier elements having the form of metallic strips 23 of revolution around a same axis 24 of revolution, spatially distributed, in any direction perpendicular to the axis 24 of revolution and passing through it, for example the direction 25 parallel to the line III-III, called the main direction of the first electrode, Is there a repetitive structure in which the distance separating, in this main direction, two metallic lamellae of consecutive revolution is defined as the pitch sBe2 of the first electrode 21. The electron multiplier device shown in FIGS. 3 and 4 also includes a electron deflector grid 22 formed by a set of deflector elements constituted, in a plane perpendicular to the axis 24 of revolution, by metallic wires 26 arranged in concentric circles, the common center 27 of which is located on the axis 24 of revolution. These metallic wires 26 are spatially distributed in any main grid direction defined by a diameter common to said concentric circles, by example the direction 28 parallel to the line III - III, in a repetitive structure whose pitch Pg2, called grid pitch, is defined by the distance between two consecutive concentric circles, and is substantially equal to the pitch Pe2 of the first electrode.

 FIGS. 5 and 6 represent a third embodiment of an electron multiplier device according to the invention, comprising a first multiplier electrode 31 of the "channel plate" type, in which the multiplier elements are channels 33 passing through a plate metallic 34 over its entire thickness. These channels carry on their wall 35 a layer of a secondary emission material. In the embodiment of the invention shown in Figures 5 and 6, the channels 33 are spatially distributed in locations forming a two-dimensional network defined by two main directions, called first direction 36 and second direction 37, forming an angle A between them which is equal to 900 in the case of FIGS. 5 and 6. The steps of the first electrode in the directions 36 and 37 are respectively Pe3 and P'e3 the step being equal to the step P'e3. The electron multiplier device of Figures 5 and 6 further comprises two grids 52 deflecting electrons, each of these grids being constituted by two networks, called first 53 and second 54 network, of metallic wires 55, 56 parallel and coplanar, spatially distributed, in directions 57, 58 , called main grid directions respectively substantially parallel to the main directions 3c, 37 of the first electrode, in two repeating structures whose steps pg4, plg4 are equal to half d are not 3, e3 corresponding to the first electrode 31. The metal wires 55, 56 of each of the networks 53, 54 are deduced from one another by a translation whose direction and module correspond respectively to direction 57, 58 main grid and at pg4, plg4 of grid, the main directions 57 and 58 of grid making between them the angle A, taken equal to 900. The grids 52 are brought to electric potentials Vg and V'g which can possibly be equal.

 FIG. 6 shows trajectories 59, 60 of incident electrons crossing the deflector grid before secondary emission.

 Figures 7 and 8 show a fourth embodiment of an electron multiplier device according to the invention also comprising a first multiplier electrode 71 of the "channel plate" type whose channels 33 are spatially distributed in locations forming a network two-dimensional in which the main direction of pitch Pe3 s P'e3 given is constituted by a first direction 36 and a second direction 37 making between them an angle of 600. The electron multiplier device shown in FIGS. 7 and 8 further comprises a deflector grid 72 of electrons in which the deflector elements consist of metallic wires forming a plurality of hexagons 73 having a center of symmetry 74 located on the axis 75 of the channels 33, the directions of the sides of said hexagons 73 being coincident with the directions of the perpendicular bisectors of the segments joining two consecutive centers of symmetry 74.

On the other hand, it is expected that two opposite vertices 76,77 of each hexagon are connected by a metallic wire 78 which, brought to the repulsive potential Vg of the grid, is intended to repel those of the incident electrons whose trajectories would cross channels 33 directly without being multiplied. The hexagons 73 form a two-dimensional network in which the main grid direction of pitch pg3, P'g3 p 'given is constituted by the first direction 36 and the second direction 37 of the first electrode 71, the grid pitch Pg3, plg) being equal to the pitch of the first electrode.

 FIG. 9 represents, in cross-section, the diagram of a photomultiplier tube equipped with an electron multiplier device 61 according to the invention. In the application example of FIG. 9, the first electrode 31, of the channel plate type ", constitutes the first dynode of the photomultiplier tube. This first dynode 31 is associated with two deflecting grids 52, similar to those previously described in relation to FIGS. 7 and 8, and placed between the first dynode 31 and the photocathode 62 of the photomultiplier tube. Thus the photoelectrons 63 originating from the photo cathode 62, the trajectories of which are substantially normal to the plane of the first dynode 31, are deflected by the deflecting grids 52 so as to limit the number of photoelactrons passing directly through the channels 31 or reaching the first dynode 31 between said channels. This arrangement makes it possible to significantly increase the collection efficiency of the first dynode 31, and to limit the dispersions of the electron transit time between the first dynode 31 and the second dynode 64. In the application example given in FIG. 9, the higher order dynodes have the same structure as the first dynoda. The photoelectric signal consists of all of the electrons arriving on the anode 65.

Claims (9)

1. Electron multiplier device by secondary emission, comprising in particular a first multiplier electrode constituted by a set of electron multiplier elements spatially distributed, at least in one direction, called main direction, in a repetitive structure of given step, said first electrode being brought to a given electrical potential, characterized in that it also comprises at least one electron deflecting grid constituted by a set of deflecting elements spatially distributed, at least in one direction, called the main grid direction, in a repetitive structure of given pitch, called grid pitch, and in that the main grid direction is substantially parallel to the main direction of the first electrode, the grid pitch being equal to the pitch of the first electrode or to a sub- multiple of this step, and in that said deflecting grid is brought to another given electrical potential, called gr potential illa. 2. Electron multiplier device according to claim 1, characterized in that the gate potential is lower than the potential of the first electrode. 3. electron multiplier device according to one of claims 1 or 2, and of which the first multiplier electrode (11) is constituted by a set of electron multiplier elements having the shape of metallic lamellae (13) plane, parallel , deducing from each other by a first translation, the direction (15) and the module (pu1) of which correspond respectively to the main direction and to the pitch of the first electrode, characterized in that the assembly (12) deflector elements is constituted by a network of metal blades (16), parallel and perpendicular to the main direction of the first electrode, deducing from each other by a second translation, the direction (17) and the module (pg1 ) correspond respectively to the main grid direction and the grid pitch. 4. Electron multiplier device according to one of claims 1 or 2, and of which the first multiplier electrode (21) is constituted by a set of electron multiplier elements having the form of metallic lamellae (23) of revolution around of the same axis (24) of revolution, the main direction of the first electrode being defined by any direction (25) perpendicular to and passing through the axis (24) of revolution, and the distance (pue2) separating , in this direction (25), two consecutive metallic lamellae of revolution being defined as the pitch of the first electrode (21), characterized in that the assembly (22) of the deflecting elements consists, in a plane perpendicular to the axis (24) of revolution, by metallic wires (26) arranged in concentric circles whose common center (27) is located on said axis (24) of revolution, the main grid direction being defined by the direction (28) of any diameter common to said ce concentric circles, and the distance (pu2) between two consecutive concentric circles being equal to the grid pitch. 5. Electron multiplier device according to one of claims <or 2, and the first electrode (31) of which is of the "channel plate" type, said channels (33) passing through said plate (34) over its entire thickness in locations forming a two-dimensional network in which said main direction of pitch (pue3 e3 P'e3) given consists of a first direction (36) and a second direction (37) forming an angle A between them, characterized in that l assembly (52) of deflector elements is constituted by two networks, called first (53) and second (54) networks, of metallic wires (55,56) parallel and coplanar, the metallic wires (55,56) of each of the networks (53,54) deducing from each other by a translation whose direction and modulus correspond respectively to said main direction (57,58) of the grid and to said pitch (pg4, p'g4) of the grid, and in that the direction pr; grid (57) grid of the first network (53) makes the angle A with the main grid direction (58) of the second network (54). 6. Electron multiplier device according to claim 5, characterized in that, according to each main direction common to the grid and to the first electrode, the grid pitch (pg4, p'g4) is equal to half the pitch ( P, 3 e3) correspondent of the first electrode. 7. Electron multiplier device according to one of claims 5 or 6, characterized in that the angle A is substantially equal to 900.  e3 a given is constituted by a first direction (36) and a second direction (37) forming an angle of 600 between them, characterized in that the assembly (72) of the deflector elements is constituted by metallic wires forming a plurality of hexagons (73) having a center of symmetry (74) located on the axis (75) of the channels (33), the directions of the sides of said hexagons (73) being coincident with the directions of the perpendicular bisectors of the segments joining two centers of symmetry (74) consecutive, while two opposite vertices (7w, 77) of each hexagon (73) are connected by a metal wire (78), and in that said hexagons (73) form a two-dimensional network in which said main direction of pitch grid (pg3, p 'g3) given is constituted by the first direction (36) and the second direction (37) of the first electrode (71), the grid pitch (pg3, p'g3) being equal to the pitch (pe3, p'e3) of the first electrode.  8. Electron multiplier device according to claim 1 or claim 2, the first electrode (71) of which is of the channel plate type, said channels (33) passing through said plate (34) over its entire thickness at locations forming a two-dimensional network in which said main direction of pitch (pe3, p'e3) 9. Application of the electron multiplier device according to any one of claims 1 to 8 to the production of a photomultiplier tube, characterized in that, said first multiplier electrode (31) constituting the first dynode of the photomultiplier tube, said grid deflector (52) is located between this first dynode (31) and the photocathode (62) of the photomultiplier tube.