EP3912183B1 - Elementary particle detector - Google Patents

Description

The invention relates to an elementary particle detector and a method for detecting elementary particles. The invention also relates to an information recording medium for the implementation of this method for detecting elementary particles.

• une cathode et une grille conductrice apte à créer une différence de potentiels susceptible d'accélérer des électrons en direction de la grille conductrice, la grille conductrice étant apte à être traversée par les électrons accélérés,
• une dynode interposée entre la cathode et la grille conductrice, cette dynode étant apte, pour chaque particule élémentaire, à produire une avalanche d'électrons secondaires, cette dynode comportant à cet effet plusieurs canaux, chaque canal comportant un matériau émissif, ce matériau émissif étant apte, en réponse à un impact d'un électron, à générer, en moyenne, plus d'un électron secondaire,
• une plaque de lecture disposée du côté de la grille conductrice opposé à la dynode, cette plaque de lecture comportant :
  • une face extérieure agencée de manière à être percutée par l'avalanche d'électrons secondaires, et
  • des électrodes disposées les unes à côtés des autres dans une face parallèle à ou confondue avec la face extérieure,
• des premiers capteurs aptes à mesurer la quantité de charges électriques sur les électrodes,
• une unité de traitement apte à déterminer l'emplacement de l'avalanche d'électrons à partir de la quantité de charges électriques mesurée par les premiers capteurs et à partir de l'emplacement connu des électrodes.

Known detectors of elementary particles include:

• a cathode and a conductive grid able to create a potential difference capable of accelerating electrons in the direction of the conductive grid, the conductive grid being able to be crossed by the accelerated electrons,
• a dynode interposed between the cathode and the conductive grid, this dynode being capable, for each elementary particle, of producing an avalanche of secondary electrons, this dynode comprising for this purpose several channels, each channel comprising an emissive material, this emissive material being capable, in response to an impact of an electron, of generating, on average, more than one secondary electron,
• a reading plate arranged on the side of the conductive grid opposite the dynode, this reading plate comprising:
  • an outer face arranged so as to be struck by the avalanche of secondary electrons, and
  • electrodes arranged side by side in a face parallel to or coincident with the outer face,
• first sensors able to measure the quantity of electrical charges on the electrodes,
• a processing unit capable of determining the location of the avalanche of electrons from the quantity of electrical charges measured by the first sensors and from the known location of the electrodes.

For example, such an elementary particle detector is known from patent US6384519B1 .

Such detectors operate correctly to determine a position of the point of impact of the elementary particle and an instant of arrival of this elementary particle. However, it is desirable to improve the precision on the measurement of this position and/or of the instant of arrival.

The invention therefore aims to propose an elementary particle detector in which the precision of the measurement of the position of the point of impact and/or the precision of the measurement of the instant of arrival of the elementary particle are improved. It therefore relates to such a detector of elementary particles according to claim 1.

The invention also relates to a method for detecting an elementary particle using the claimed detector.

Finally, the invention also relates to an information recording medium, readable by an electronic computer, this recording medium comprising instructions for the execution of the method for detecting elementary particles, when these instructions are executed by the electronic calculator.

• la figure 1 est une illustration schématique, en coupe verticale, d'un premier mode de réalisation d'un détecteur de particules élémentaires ;
• la figure 2 est une illustration schématique et partielle en coupe verticale d'un canal d'une dynode du détecteur de la figure 1 ;
• les figures 3 et 4 sont des illustrations schématiques de différents positionnements possibles des canaux d'une dynode supérieure par rapport aux canaux d'une dynode inférieure dans un détecteur tel que le détecteur de la figure 1 ;
• la figure 5 est une illustration schématique d'un pic de charges susceptible d'être mesuré par une plaque de lecture du détecteur de la figure 1 ;
• la figure 6 est une illustration schématique d'un pic de charges susceptible d'être mesuré sur une grille conductrice du détecteur de la figure 1 ;
• la figure 7 est une illustration schématique et en vue de dessus d'une grille conductrice du détecteur de la figure 1 ;
• la figure 8 est une illustration schématique partielle, en coupe verticale, d'une plaque de lecture du détecteur de la figure 1 ;
• la figure 9 est une illustration schématique, partielle et en vue de dessus, de l'agencement de différentes électrodes, les unes par rapport aux autres, de la plaque de lecture de la figure 8 ;
• la figure 10 est un organigramme d'un procédé de détection de particules élémentaires à l'aide du détecteur de la figure 1 ;
• la figure 11 est une illustration schématique et partielle, en coupe verticale, d'un autre mode de réalisation d'une plaque de lecture ;
• la figure 12 est un organigramme d'un procédé de détection de particules élémentaires en utilisant la plaque de lecture de la figure 11 ;
• la figure 13 est une illustration schématique et en vue de dessus d'un autre mode de réalisation d'une grille conductrice pour le détecteur de la figure 1 ;
• la figure 14 est une illustration schématique, partielle et en vue de dessus, d'un autre agencement possible des différentes électrodes de la plaque de lecture.

The invention will be better understood on reading the following description, given solely by way of non-limiting example and made with reference to the drawings in which:

• there figure 1 is a schematic illustration, in vertical section, of a first embodiment of an elementary particle detector;
• there figure 2 is a schematic and partial illustration in vertical section of a channel of a detector dynode of the figure 1 ;
• THE figures 3 and 4 are schematic illustrations of different possible positionings of the channels of an upper dynode relative to the channels of a lower dynode in a detector such as the detector of the figure 1 ;
• there figure 5 is a schematic illustration of a peak of charges likely to be measured by a reading plate of the detector of the figure 1 ;
• there figure 6 is a schematic illustration of a charge peak likely to be measured on a conductive grid of the detector of the figure 1 ;
• there figure 7 is a schematic and top view illustration of a conductive grid of the detector of the figure 1 ;
• there figure 8 is a partial schematic illustration, in vertical section, of a detector reading plate of the figure 1 ;
• there figure 9 is a schematic illustration, partial and in top view, of the arrangement of different electrodes, relative to each other, of the reading plate of the figure 8 ;
• there figure 10 is a flowchart of a method for detecting elementary particles using the detector of the figure 1 ;
• there figure 11 is a schematic and partial illustration, in vertical section, of another embodiment of a reading plate;
• there figure 12 is a flowchart of a method for detecting elementary particles using the reading plate of the figure 11 ;
• there figure 13 is a schematic and top view illustration of another embodiment of a conductive grid for the detector of the figure 1 ;
• there figure 14 is a schematic illustration, partial and in plan view, of another possible arrangement of the various electrodes of the reading plate.

In these figures, the same references are used to designate the same elements. In the remainder of this description, the characteristics and functions well known to those skilled in the art are not described in detail.

Chapter I: Examples of embodiments

There figure 1 represents a detector 2 of elementary particles. Detector 2 is a detector known by the term "microchannel pancake detector" or under the English term "MicroChannel Plate Detector". In this embodiment, the elementary particles to be detected are photons.

The general architecture and the operating principle of such a detector are known. For example, the reader can refer to the patent US6384519B1 . Thus, hereafter, only the details necessary to understand the invention are described in detail.

In this application, the figures are oriented with respect to an orthogonal reference XYZ, where Z is the vertical direction which points upwards. Terms such as "upper", "lower", "up", "down", "above" and "below" are defined relative to the Z direction.

• une cathode 4,
• une dynode supérieure 6,
• une grille conductrice supérieure 8,
• une dynode inférieure 10,
• un grille conductrice inférieure 12,
• un espaceur 14, et
• une plaque 16 de lecture.

Detector 2 comprises successively, going from top to bottom, the following different elements:

• a cathode 4,
• an upper dynode 6,
• an upper conductive grid 8,
• a lower dynode 10,
• a lower conductive grid 12,
• a spacer 14, and
• a plate 16 of reading.

These different elements essentially each extend in a horizontal plane. They are therefore much wider than high. They are also directly stacked on top of each other. However, to increase the readability of the figure 1 , in this figure, these different elements are spaced vertically from each other.

The cathode 4 is made of a material which is also electrically conductive or resistive. The cathode 4 is connected to a terminal 20 of a power source 22 which delivers a potential HV1. The cathode 4 is generally made of an emissive material which generates at least one electron when an elementary particle strikes it. In the particular case where the elementary particle is a photon, this cathode is known by the term “photocathode”.

By "electrically conductive material" or "conductive material" is meant here a material whose resistivity at 20° C. is less than 10 ^-2 Ω.m and, preferably, less than 10 ^-5 Ω.m or 10 ^-6 Ω.m. Generally, the resistivity of an electrically conductive material at 20°C is greater than 10 ^-10 Ω.m.

By "electrically resistive material" or "resistive material" is meant here a material whose resistivity at 20° C. is less than 10 ¹² Ω.m and, preferably, less than 10 ⁶ Ω.m or 10 ⁴ Ω.m .

Dynode 6 is located just below cathode 4. Dynode 6 is a microchannel plate known by the acronym MCP (“Micro-Channel Plate”). It is crossed vertically, from side to side, by several million channels often called “microchannels”. On the figure 1 , only a few channels 24 are schematically represented. In this embodiment, each channel runs along a vertical axis 26.

The density of channels 24 per unit horizontal area is typically greater than one thousand channels per square centimeter or 10,000 channels per square centimeter or 100,000 channels per square centimeter. Here, the density of channels per square centimeter is very important. For example, this density is greater than 1 million channels per square centimeter or greater than 3 million channels per square centimeter. For this purpose, the average diameter Dm24 of the channels 24 is very small, that is to say, generally less than 100 μm or 50 μm or 10 μm. This diameter Dm24 is also usually greater than 10 nm or 50 nm.

By "mean diameter" is meant the unweighted or arithmetic average of the diameters of all cross-sections of channel 24 along its axis 26. The cross-sections are horizontal. Moreover, when the cross-section of the channel 24 is not circular, the term "diameter" designates the hydraulic diameter of this cross-section.

Here, the cross section of channel 24 is circular. Moreover, this cross-section is constant over the entire length of the channel 24. The length of the channel 24 in the Z direction is conventionally greater than its diameter Dm24 or 2*Dm24 or 10*Dm24. In this description, the symbol "*" designates the multiplication operation. This length is also usually less than 500*Dm24 or 100*Dm24 or 50*Dm24.

The shortest horizontal distance which separates the axes 26 of two channels 24 located one beside the other is usually less than 4*Dm24 or 2*Dm24.

• une entrée 28 (figure 2) par l'intermédiaire de laquelle les électrons à amplifier pénètrent à l'intérieur du canal 24, et
• une sortie 30 (figure 2) par l'intermédiaire de laquelle les électrons amplifiés s'échappent du canal 24.

Each channel 24 includes:

• an entry 28 ( figure 2 ) through which the electrons to be amplified enter the channel 24, and
• an output 30 ( picture 2 ) through which the amplified electrons escape from channel 24.

At least the upper part of the vertical walls of the channel 24 consists of an emissive coating 32 ( picture 2 ). When the liner 32 forms only part of the vertical wall of the channel 24, it typically forms more than a quarter or more than a third of the height of this vertical wall. Here, the emissive coating 32 extends the full length of the channel 24.

The coating 32 is made of an emissive material which, on average, when struck by an electron generates in response more than one secondary electron and preferably more than 1.5 or 2 secondary electrons. For example, the emissive material used to produce the coating 32 is chosen from the group consisting of the emissive materials listed between lines 6 to 44 of column 10 of US6384519B1 .

Apart from the channels 24 and the coatings 32, the dynode 6 includes a matrix 34 in which these channels 24 are cut. The matrix 34 can be made of a resistive material or a dielectric material. By “dielectric material”, is meant here a material whose resistivity at 20° C. is greater than or equal to 10 ¹² Ω.m and, preferably, greater than or equal to 10 ¹⁴ Ω.m or 10 ¹⁶ Ω.m. Generally, the resistivity of a dielectric material at 20°C is less than 10 ²⁸ Ω.m. A resistive material is a material whose resistivity is between those of dielectric materials and conductive materials.

The grid 8 in combination with the cathode 4 generates an electric field suitable for accelerating downwards the electrons located and generated inside each of the channels 24. For example, the electric field generated is between 1 kV/cm 50 kV/cm.

To this end, the grid 8 is made of a conductive material, such as a metal. It is connected to a terminal 36 of the source 22 which delivers a potential HV2 greater than the potential HV1. The difference between the potentials HV1 and HV2 is, for example, greater than 10 volts or 100 volts and generally less than 5000 volts or 2000 volts.

The grid 8 is also, as far as possible, transparent to the electrons accelerated and expelled by the outputs 30 of the channels 24. Such a grid is known under the name of “Frisch grid” or “Frisch grid” in English.

The degree of transparency of a conductive grid is defined as being the value, expressed in %, of the ratio between the number of electrons passing through this grid divided by the number of electrons projected onto this grid. This rate of transparency is generally between 30% and 95% or between 45% and 90%. For example, here it is greater than 60% or 70%.

To this end, the grid 8 is pierced with a multitude of small holes 38, only a small number of which are schematically represented on the figure 1 . Typically, the diameter D38 of the holes 38 is less than 50 μm or 100 μm. To obtain a high degree of transparency, the cumulative surfaces of the cross sections of the holes 38 represent more than 30% or 45% and, preferably, more than 60% or 70% of the smallest surface of the conductive grid containing all these holes 38.

Typically, the thickness of the grid 8 is small compared to the diameter D38 of the holes, ie the thickness of the grid is generally less than the diameter D38 or 0.5*D38.

The impedance of gate 8 is uniform. For example, here, it is considered that the impedance of the grid is uniform if the impedance between any two points A and B of the grid 8, spaced horizontally from each other by a constant horizontal distance, is systematically included between 0.95Z _AB and 1.05Z _AB and this whatever the chosen horizontal distance, where Z _AB is a constant.

• les canaux, les entrées et les sorties de ces canaux portent, respectivement, les références numériques 40, 42 et 44, et
• le diamètre Dm40 de ces canaux 40 est différent du diamètre Dm24.

Dynode 10 is identical to dynode 6 except that:

• the channels, the inputs and the outputs of these channels carry, respectively, the numerical references 40, 42 and 44, and
• the diameter Dm40 of these channels 40 is different from the diameter Dm24.

The dynode 10 is positioned relative to the dynode 6 so that the electrons which escape from the outlet 30 of a channel 24 are distributed in several channels 40. For example, for this purpose, the orthogonal projection, on a horizontal plane containing the inputs 42, of the cross section of the output 30 of each channel 24 covers, at least partially, at least two inputs 42. Thanks to this, the electrons escaping from the outlet 30 are distributed in several of the channels 40 of the dynode 10.

For this, in a first embodiment, the diameter Dm40 is less than the diameter Dm24 and, preferably, less than 0.8*Dm24 or 0.5*Dm24. This embodiment is illustrated in the picture 3 . In this figure, the orthogonal projection of the output 30 of a channel 24 on the horizontal plane containing the inputs 42 is represented by a dotted circle which bears the same reference as the output 30.

In another embodiment, the diameter Dm40 is equal to or greater than the diameter Dm24. In this case, the channels 40 are horizontally offset from the channels 24. By way of illustration, this is shown in the figure 4 in the particular case where the diameters Dm40 and Dm24 are equal.

The grid 12 is identical to the grid 8, except that the holes bear the reference numerals 50. Moreover, the diameter D50 of the holes 50 is not necessarily equal to the diameter D38. Indeed, if necessary, it is adapted to obtain a transparency rate greater than 60% or 80%. For example, the D50 diameter is adapted according to the Dm40 diameter.

Gate 12 is connected to a terminal 52 of source 22 which generates a potential HV3. The potential HV3 is higher than the potential HV2 to create an electric field in the channels 40 which makes it possible to accelerate the secondary electrons towards the gate 12. For example, the potential HV3 is adjusted to generate an electric field identical to that generated in the channels 24.

The spacer 14 separates the dynode 10 from the reading plate 16. More specifically, it provides an empty space 56 between the outputs 42 of the channels 40 and a horizontal outer face 60 of the plate 16. This empty space 56 is crossed by the avalanche of secondary electrons which emerge from the outputs 44 of the dynode 10 when an elementary particle is detected. This space 56 increases the spatial dispersion of these secondary electrons, in particular, in the horizontal direction. Thus, the surface of the impact zone of the secondary electrons of the avalanche on the outer face 60 is greater in the presence of the spacer 14 than in its absence. For example, the spacer 14 is arranged so that the distance between the horizontal plane containing the outlets 44 and the outer face 60 is greater than 10 μm or 15 μm and generally less than 300 μm or 200 μm.

The combination of cathode 4, dynode 6, grid 8, dynode 10 and grid 12 forms an electrical charge amplification device. More specifically, each time an electron is generated by the cathode 4 and enters one of the channels 24, the probability is high that it strikes the coating 32, which, in response, causes the generation, on average, of more of a secondary electron. These secondary electrons are accelerated in turn and collide again with the coating 32, which multiplies the number of secondary electrons and causes what is called an avalanche of secondary electrons. The secondary electrons penetrate inside the channels 40 and the same phenomenon of demultiplication of the secondary electrons occurs in these channels 40. Thus, each elementary particle that strikes the cathode 4 causes the appearance of an avalanche of secondary electrons which is then projected onto the outer face 60 of the plate 16. The location of this avalanche of secondary electrons on the outer face 60 is representative of the position of the point of impact of the elementary particle on the cathode 4. It is therefore necessary to determine the location of the avalanche of secondary electrons in order to be able to deduce the position of this point of impact. The plate 16 makes it possible, in particular, to determine the location of this avalanche of secondary electrons in a horizontal plane.

• un substrat 61 dont la face supérieure forme la face extérieure 60, et
• des bandes conductrices 62 qui s'étendent horizontalement sur la face extérieure 60.

To this end, the plate 16 comprises in particular:

• a substrate 61 whose upper face forms the outer face 60, and
• conductive strips 62 which extend horizontally on the outer face 60.

Each strip 62 is electrically isolated from the other conductive strips 62 present in the plate 16. Each strip 62 extends mainly horizontally from a distal end to a proximal end. The distal and proximal ends of each band 62 are located on one edge of the plate 16. The arrangement of the bands 62 is described in more detail with reference to the figures 8 and 9 .

Since the bands 62 are located on the exterior face 60, they are directly exposed to the secondary electrons of each avalanche. Thus, when the electrons of an avalanche reach a band 62 this generates a peak of characteristic charges on this band. Such a load peak 64 is schematically represented on the graph of the figure 5 . On this graph, as well as on the graph of the figure 6 , the abscissa axis represents time and the ordinate axis represents the quantity of electric charges. This peak 64 begins at a time t ₁ and ends at a time t ₂ . The times t ₁ and t ₂ correspond to times when the quantity of charges on the strip 62, respectively, exceeds and falls below a predetermined threshold. Indeed, the secondary electrons of the same avalanche do not all arrive at the same time and at the same place on the strip 62 because they have not all followed the same route.

To detect or measure such charge peaks, each strip 62 is connected to a respective input of a sensor 70 of electrical charges. To this end, the detector 2 comprises a set 72 of sensors which comprises at least as many sensors 70 as there are bands 62.

To simplify the figure 1 , a single conductive strip 62 and a single sensor 70 are shown.

• à signaler le franchissement du seuil prédéterminé par la quantité de charges électriques tant que ce seuil est franchi, ou
• à systématiquement générer une grandeur électrique représentative de la quantité de charges électriques actuellement présentes sur la bande conductrice.

The sensor 70 is capable of measuring a physical quantity representative of the quantity of electrical charges present on the strip 62 to which it is connected. In this embodiment, the sensor 70 rapidly measures the quantity of electrical charges present on this conductive strip 62. The measurement of the quantity of electrical charges on a strip can consist of:

• to signal the crossing of the predetermined threshold by the quantity of electric charges as long as this threshold is crossed, or
• systematically generating an electrical quantity representative of the quantity of electrical charges currently present on the conductive strip.

• une mémoire 82, et
• un microprocesseur 84 programmable apte à exécuter des instructions enregistrées dans la mémoire 82.

The detector 2 also comprises a processing unit 80 connected to each of the sensors 70. The processing unit 80 is capable of acquiring the measurements of the sensors 70. Then, the unit 80 automatically determines, from the measurements of the sensors 70 and the known arrangement of conductive strips 62, the location of the second avalanche of secondary electrons. From the location of the second avalanche, the unit 80 establishes the position of the point of impact between the elementary particle and the cathode 4. For this purpose, the processing unit 80 comprises:

• a memory 82, and
• a programmable microprocessor 84 capable of executing instructions stored in memory 82.

The memory 82 contains the instructions and the data necessary for the execution of the method of the figure 10 .

Finally, the detector 2 comprises a set 90 of one or more sensors 92 each capable of measuring a time at which the avalanche of secondary electrons crosses the grid 8. Subsequently, this time is called "crossing time". Here, each of these sensors is electrically connected to the grid 8. The assembly 90 here comprises four sensors 92 individually designated by the references 92a to 92d on the figure 7 . To simplify the figure 1 , only one of these sensors 92 is shown in this figure. In this first embodiment, each sensor is for example connected to a respective point on the periphery of the grid 8. The connection points of the sensors 92a to 92d are denoted, respectively, P _92a to P _92d . Here, these points P _92a to P _92d are uniformly distributed over the periphery of the grid 8.

• l'impédance de la grille 8 est beaucoup plus uniforme que l'impédance des bandes conductrices 62, et
• au moment où l'avalanche d'électrons secondaires traverse la grille 8, les électrons secondaires sont moins dispersés spatialement qu'au moment où cette avalanche percute la plaque 16.

Par contre, la quantité d'électrons secondaires est moindre au niveau de la grille 8.Each sensor 92 is designed to measure the characteristic electrical signal which appears when the grid 8 is crossed by an avalanche of secondary electrons. More precisely, when an avalanche of secondary electrons crosses the grid 8, this causes, by electromagnetic induction, the appearance of a peak of charges in the grid 8. Such a peak 94 of charges is represented on the graph of the figure 6 . Peak 94 begins at a time t ₃ and ends at a time t ₄ . For example, the times t ₃ and t ₄ are the times when the quantity of electrical charges measured by the sensor 92, respectively, exceeds then falls below a predetermined threshold. It will be noted that peak 94 is much narrower than peak 64 and therefore times t ₃ and t ₄ are closer to each other than times t ₁ and t ₂ . In effect :

• the impedance of the gate 8 is much more uniform than the impedance of the conductive strips 62, and
• when the avalanche of secondary electrons crosses the grid 8, the secondary electrons are less spatially dispersed than when this avalanche hits the plate 16.

On the other hand, the quantity of secondary electrons is less at the level of gate 8.

The unit 80 is also connected to each of the sensors 92 to determine a time t _a of arrival of the elementary particle from the measurements of the sensors 92.

• une couche inférieure de métallisation 102,
• une première couche diélectrique 104,
• une première couche de métallisation intermédiaire 106,
• une deuxième couche diélectrique 108,
• une deuxième couche de métallisation intermédiaire 110,
• une troisième couche diélectrique 112, et
• une couche de métallisation supérieure 114 déposée sur la face avant de la couche diélectrique 112.

There figure 8 shows the plate 16 in vertical section along a horizontal direction V. The substrate 61 is here formed by a stack, immediately on top of each other, of horizontal layers. These stacked horizontal layers are as follows, going from bottom to top in the Z direction:

• a lower layer of metallization 102,
• a first dielectric layer 104,
• a first intermediate metallization layer 106,
• a second dielectric layer 108,
• a second intermediate metallization layer 110,
• a third dielectric layer 112, and
• an upper metallization layer 114 deposited on the front face of the dielectric layer 112.

By "dielectric layer" is meant a horizontal layer of which more than 90% of the volume is made of dielectric material.

For example, the metallization layers are made of copper.

As described in more detail with reference to figure 9 , the metallization layer 114 is structured to form horizontal tiles 120 separated horizontally mechanically from each other by interstices 124. In this text, the reference 120 is used as a generic reference to designate all the tiles made in the layer 114 Each tile 120 is completely surrounded by a gap 124. The gaps 124 are filled with a dielectric material, for example, identical to that of the dielectric layer 112. Thus, there is no electrical connection made in the layer. 114, which electrically connects two tiles 120 together. Here, 120 tiles are all identical to each other. In particular, each tile 120 is deduced from another tile 120 only by a horizontal translation possibly combined with a rotation around a vertical axis. Each tile is shaped like a polygon with all sides the same length.

The largest dimension of a tile 120 is chosen so that each avalanche of secondary electrons which touches the plate 16 strikes at least two, and in this embodiment, at least three tiles 120 belonging to different conductive strips 62 . For this purpose, the largest dimension of a tile 120 is preferably less than or equal to 5*Dm40 or 3*Dm40 and, advantageously, less than Dm40 or 0.5Dm40. By "largest dimension of a tile", we designate here the length of the longest side of the horizontal rectangle of smallest surface which entirely contains the tile 120. By "smallest dimension of a tile", we designate the length of the short side of this rectangle. The smallest dimension of a tile 120 is typically greater than 0.01*Dm40 or 0.1*Dm40 or 0.3*Dm40.

• un piste conductrice 130 réalisée dans l'une des couches de métallisation 102, 106, ou 110 et qui s'étend horizontalement entre une première extrémité située sous la première tuile 120 et une deuxième extrémité située sous la deuxième tuile 120, et
• des plots conducteurs 132, 134 verticaux, connus sous le terme de « via », qui traversent chacun une ou plusieurs des couches 104, 108 et 112 pour raccorder électriquement les première et deuxième tuiles, respectivement, aux première et deuxième extrémités de la piste 130.

To form a conductive strip 62 which extends primarily along a horizontal line 126 ( Figure 9 ) parallel to the direction V, tiles located one behind the other along this line 126 are electrically connected together in series via electrical connections 128. The connections 128 are made under the front face of the dielectric layer 112. Here, each connection 128 that electrically connects first and second tiles 120 along line 126 includes:

• a conductive track 130 made in one of the metallization layers 102, 106, or 110 and which extends horizontally between a first end located under the first tile 120 and a second end located under the second tile 120, and
• vertical conductive pads 132, 134, known by the term "via", which each pass through one or more of the layers 104, 108 and 112 to electrically connect the first and second tiles, respectively, to the first and second ends of the track 130 .

Here, in the particular case of tiles 120 aligned along line 126, track 130 is made in metallization layer 110. Vias 132, 134 therefore only cross dielectric layer 112. used to make the electrical tracks, corresponding to the track 130, for the conductive strips 62 which extend, respectively, parallel to other directions U and W. Here, the V direction is parallel to the Y direction and the U directions and W are angularly offset by, respectively, 60° and 120° with respect to the direction V.

In addition to the vias 132 and 134, each conductive strip comprises at least one additional via 136 which opens onto the underside of the layer 104 and which makes it possible to connect this strip to a respective sensor 70. The via 136 extends, for example, from one of the connections 128 to this underside of the layer 104. Consequently, the sensor 70 which measures the quantity of electric charges present on this strip 62 can be placed n anywhere on this underside and not just on the periphery of plate 16.

There figure 9 represents a first example of a possible arrangement, relative to each other, of the tiles 120 on the horizontal front face of the dielectric layer 112. In this embodiment, each tile 120 has the shape of a diamond whose two vertices 140, 142 the most pointed are located at each end of the long diagonal of this rhombus. The angle at vertices 140 and 142 is 60°.

On the figure 9 , the interstices 124 between the tiles 120 are represented by lines.

The tiles 120 are arranged relative to each other so as to form a paving, also known by the English term of "tessallation", of the front face of the dielectric layer 112. Here, the tiles 120 are distributed over the front face of the dielectric layer 112 so as to form a periodic tiling, that is to say a tiling which can be entirely constructed by periodically repeating a same pattern in at least two different horizontal directions. For example, here, the repeated pattern is a hexagon formed by three adjacent tiles 120 which carry, respectively, the numerical references 120a, 120b and 120c on the figure 9 . The large diagonals of these tiles 120a, 120b and 120c are, respectively, parallel to directions Da, Db and Dc. The direction Da is parallel to the direction X and the directions Db and De are angularly offset, respectively, by +60° and +120° with respect to the direction Da. In the repeated pattern, these three tiles 120a, 120b and 120c have a common vertex. In the case of paving the figure 9 , the pattern is repeated periodically in the Da, Db and Dc directions.

On the figure 9 , to facilitate the identification of the tiles 120a, 120b and 120c, each tile 120a, 120b and 120c is filled with a respective texture.

All the tiles 120b whose long diagonals are aligned on the line 126 are electrically connected in series to each other from one edge of the paving to the opposite edge to form a conductive strip 62 which extends parallel to the direction V. thus connecting tiles 120b aligned along line 126, each tile 120b is separated from the immediately consecutive tile 120b along line 126 by tiles 120a and 120c. Thanks to this, the precision on the measurement of the position of the elementary particle is increased. The other tiles 120b are electrically connected to each other in a similar manner to form a plurality of conductive strips 62 which extend parallel to the Y direction. The various conductive strips 62 parallel to the Y direction thus formed are electrically isolated from each other. others.

Similarly, the tiles 120a whose long diagonals are aligned one after the other along a line 144 parallel to the direction W are all electrically connected in series with each other by connections 128. Proceeding in this way for all the tiles 120a, a plurality of conductive strips 62 electrically insulated from each other and all parallel to the direction U are formed.

Finally, still in a similar way to what has been described for the tiles 120a and 120b, the tiles 120c aligned one behind the other along the same line 146 parallel to the direction U are electrically connected in series to each other. by connections 128. By proceeding in this way for all the tiles 120c, a plurality of conductive strips 62 are formed, electrically insulated from each other and all parallel to the direction U.

When the dimensions of the tiles 120 are large enough, these can be etched into the metallization layer 114 using simple etching methods such as photolithography. When the dimensions of the tiles 120 are very small, it is possible to produce them using the same manufacturing processes as those used to interconnect electronic components produced on a silicon substrate. Typically, these are the processes implemented during the manufacturing phase designated by the acronym BEOL ("Back End Of Line"). The metallization layers used to make the tiles 120 and their connections 128 are then, for example, chosen from the metallization levels known by the acronyms M1 to M8.

Since the avalanche charges spread systematically over at least three contiguous tiles 120, the avalanche causes a variation in the electrical charge of at least three conductive strips 62 which each extend in three different directions. Thus, even if two avalanches simultaneously hit the plate 16 at two different places, the processing unit 80 is capable of unambiguously determining the positions of the two simultaneous impact points if they are separated from each other by a distance greater than the largest dimension of a tile.

Here, the sensitivity of each conductive strip 62 is identical to that of the other conductive strips 62. Thus, it is not necessary to provide in the plate 16 means for compensating for the difference in sensitivity between the various conductive strips 62.

Finally, the number of sensors 70 necessary to measure the position of the point of impact of an elementary particle is much smaller than in the case where each tile 120 would be electrically isolated from all the other tiles 120 and directly connected to an input of a respective 70 sensor. Indeed, in the latter case, the assembly 72 must include as many sensors 70 as tiles 120, whereas in the embodiment described here, it only includes one sensor 70 per conductive strip 62.

The operation of detector 2 will now be described using the method of figure 10 .

During a step 150, a photon strikes the cathode 4 and the cathode 4 generates in response at least one electron which penetrates inside the channel 24 closest to the point of impact. This electron is then accelerated and strikes the coating 32, thus causing the generation of a first avalanche of secondary electrons.

The first avalanche of secondary electrons crosses the grid 8, thus generating a peak of charges, such as the peak 94. The electrons of this first avalanche penetrate inside several of the channels 40. These electrons are then once again amplified inside the channels 40. There is thus produced at the output of the dynode 10 a second avalanche of secondary electrons containing many more electrons than the first avalanche of secondary electrons.

The second avalanche crosses the grid 12 and the empty space 56 and the secondary electrons of this second avalanche strike several of the tiles 120 of the plate 16. This then generates a peak of charges such as the peak 64, on several of the conductive strips 62.

In parallel, during a step 152, the sensors 70 permanently measure the quantity of electric charges present on each of the strips 62 and transmit these measurements to the unit 80. At the same time, the sensors 92 permanently measure the quantity electrical charges present on grid 8 and transmit these measurements to unit 80.

During a step 154, for example, executed in parallel with step 152, the unit 80 processes the measurements of the sensors 70 and 92 to establish, during an operation 156, the position Pf of the point of impact of the photon on the cathode 4 and, during an operation 158, the instant t _a of arrival of this photon.

During operation 156, a location P701 is first determined from the crossing points between the conductive strips 62 on which a charge peak has been detected. The charge distribution zone of the secondary electrons of the second avalanche on the outer face 60 is located at the intersection of several bands 62 on which a charge peak is detected. Since the location of the bands 62 is known in an X,Y plane, the location of this distribution area in the X,Y plane can be determined. For example, for this purpose, the memory 82 comprises a cartography of the bands 62 encoding for each of these bands the equation of the horizontal axis along which it extends. The coordinates in the X, Y plane of the point of intersection between two strips 62 can then easily be found, since the equation of the axes of these strips is known.

In this embodiment, by way of illustration, during operation 156, the measurements of the sensors 92 are additionally used to validate or invalidate the location P701 determined from the measurements of the sensors 70.

• d_92a et d_92b sont les distances qui séparent l'emplacement P701 déterminé des emplacements, respectivement, des capteurs 92a et 92b, et
• c₈ est la vitesse de propagation du signal électrique dans la grille 8.

For example, for this, the unit 80 calculates the deviation Ee _ab . The difference Ee _ab is equal to the estimate of the difference between the instants tm _92a and tm _92b where the load peak is detected by the sensors, respectively, 92a and 92b. This difference Ee _ab is, for example, estimated using the following relationship: Ee _ab = (d _92a -d _92b )/c ₈ , where

• d _92a and d _92b are the distances which separate the location P701 determined from the locations, respectively, of the sensors 92a and 92b, and
• c ₈ is the propagation speed of the electric signal in the gate 8.

The locations of sensors 92a and 92b in the X,Y plane are known and, for example, stored in memory 82.

The deviation Ee _ab is then compared with the measured deviation Em _ab . The deviation Em _ab is equal to the difference tm _92a -tm _92b , where the instants tm _92a and tm _92b are the instants measured when, respectively, the sensors 92a and 92b detect the load peak.

If the difference, in absolute value, between the deviations Ee _ab and Em _ab is greater than a threshold S1, then the location P701 is considered invalid. Otherwise, it is considered valid.

The verification of the validity of the location P701 is tested, as described above, in the particular case of the sensors 92a and 92b, by successively using the other possible pairs of sensors 92. If the determined location P701 is validated with the measurements from each of the sensors 92, then location P701 is considered valid. For example, in this case, the position Pf of the point of impact is taken equal to this location P701. Otherwise, location P701 is considered invalid. In the latter case, the method stops and returns to an initial state to determine the position of the point of impact of the next elementary particle received.

Then, during operation 158, unit 80 establishes the time t _a of arrival of the elementary particle. For this, in this embodiment, a time t _a92 of arrival of the elementary particle is determined from the measurements of the sensors 92. To this end, the unit 80 records the times tm _92a , tm _92b , tm _92c and tm _92d where the sensors, respectively, 92a, 92b, 92c and 92d have detected a load peak such as peak 94. For example, each of these instants tm ₉₂ is established from the instants corresponding to instants t ₃ and t ₄ of peak 94.

Then, each of these instants tm _92a to tm _92d is corrected by subtracting from it the propagation time of the electric signal between the location where the first avalanche crosses the grid 8 and the location of the sensor 92. Subsequently, the instants tm _92a to tm _92d corrected are denoted, respectively, tc _92a to tc _92d .

• c₈ est la vitesse de propagation du signal électrique dans la grille 8, et
• d_92a est la distance entre l'emplacement où la première avalanche traverse la grille 8 et l'emplacement du capteur 92a.

For example, the instant tc _92a is calculated using the following relationship: tc _92a =tm _92a -d _92a /c ₈ , where:

• c ₈ is the propagation speed of the electric signal in the grid 8, and
• d _92a is the distance between the location where the first avalanche crosses the grid 8 and the location of the sensor 92a.

The location where the first avalanche crosses the grid 8 is established from the position Pf determined during operation 156. For example, the coordinates of this location are taken equal to the x,y coordinates of the position Pf. The coordinates of the sensor 92a in the plane X, Y are known and, for example, pre-recorded in the memory 82.

The other corrected instants tc _92b , tc _92c and tc _92d are typically calculated in a similar way, but by replacing the distance d _92a by the appropriate distance.

The arrival time t _a92 of the elementary particle is then determined from the corrected times tc _92a to tc _92d . For example, time t _a92 is equal to the arithmetic mean of times tc _92a to tc _92d . Here, the instant t _a of arrival of the elementary particle is for example taken equal to the instant t _a92 thus determined.

There figure 11 represents a reading plate 200 capable of being used instead of plate 16. This plate 200 is identical to plate 16, except that two sensors 70 ₁ and 70 ₂ are connected to each end of each conductive strip 62. For simplify the figure 11 , a single band 62 is shown. The wavy and vertical lines indicate that a central part of plate 200 has not been represented on the figure 11 . The via 136 is replaced by two vias 202 and 204 each located at a respective end of the strip 62. The sensors 70 ₁ and 70 ₂ are connected, respectively, to the vias 202 and 204. Each of the sensors 70 ₁ and 70 ₂ is identical to sensor 70.

• une opération 210 d'établissement de la position Pf du point d'impact, et
• une opération 212 d'établissement de l'instant t_a d'arrivée de la particule élémentaire.

The operation of a detector equipped with the plate 200 will now be described with reference to the method of the figure 12 . The process of figure 12 is identical to the process of figure 10 , except that step 154 is replaced by a step 208. Step 208 successively comprises:

• an operation 210 for establishing the position Pf of the point of impact, and
• an operation 212 for establishing the time t _a of arrival of the elementary particle.

Operation 212 is identical to operation 156, except that it comprises, in addition or instead, the determination of a location P702 of the second avalanche of secondary electrons from instants tm ₇₀₁ and tm ₇₀₂ where the sensors 70 ₁ and 70 ₂ detect the presence of a peak of charges, such as the peak 64. For example, each instant tm ₇₀₁ and tm ₇₀₂ is determined from the instants corresponding to the instants t ₁ and t ₂ of the peak 64 For at least one of the strips 62 affected by the second avalanche, the location P702 along this strip 62 is determined from the coordinates xc ₆₂ , yc ₆₂ of the midpoint located halfway between the sensors 70 ₁ and 70 ₂ and times tm ₇₀₁ and tm ₇₀₂ . For example, the coordinates x _2i , y _2i of the location P702 are taken equal to the coordinates xc ₆₂ , yc ₆₂ to which are added the distance (tm ₇₀₁ -tm ₇₀₂ )*c ₁₆ , where c ₁₆ is the speed of propagation of the electrical signal in the band 62. Indeed, the times tm ₇₀₁ and tm ₇₀₂ are equal, only if the second avalanche is located on the midpoint. In all the other cases, that is to say as soon as the second avalanche is offset with respect to the midpoint, the instants tm ₇₀₁ and tm ₇₀₂ are different. The difference between times tm ₇₀₁ and tm ₇₀₂ is proportional to the shift of the second avalanche with respect to the midpoint.

The above calculation is preferably carried out for several of the strips 62 on which a charge peak is detected. For each of these bands 62, a location P702 is obtained. These different P702 locations are then combined to obtain more precise x _2i , y _2i coordinates.

If the coordinates x _1i , y _1i of the location P701 have been determined from the crossing points of the conductive strips 62 on which a charge peak has been detected, advantageously, these are combined with the coordinates x _2i , y _2i to obtain more precise coordinates of the second avalanche. For example, the coordinates of the second avalanche are obtained by carrying out an arithmetic or weighted average of the coordinates x _1i , y _1i , and x _2i , y _2i . For example, the weight given to coordinates x _2i , y _2i is less than that given to coordinates x _1i , y _1i . Then, for example, the x,y coordinates of the position Pf of the point of impact are taken equal to the more precise coordinates thus determined.

Operation 212 is identical to operation 158, except that it comprises, in addition or instead, the determination of a time t _a70 of arrival from the measurements of the sensors 70 ₁ and 70 ₂ connected to a band 62 affected by the second avalanche of secondary electrons.

For example, for this strip 62, each instant tm ₇₀₁ and tm ₇₀₂ is first corrected to subtract from it the propagation time of the electrical signal between the location of the second avalanche and the location of each of the sensors 70 ₁ and 70 ₂ . For this, the coordinates of the location where the second avalanche touches the plate 16 are established from the coordinates of the position Pf determined during operation 210. The coordinates of each of the sensors 70 ₁ and 70 ₂ in the plane X , Y are known and, for example, pre-recorded in the memory 82. For example, a time tc ₇₀₁ corrected for time tm ₇₀₁ is calculated using the following relationship tc ₇₀₁ =tm ₇₀₁ -d ₇₀₁ /c ₁₆ , where d ₇₀₁ is the distance between the coordinates of the second avalanche along the strip 62 and the coordinates of the sensor 70 ₁ in the X, Y plane.

The corrected instant tc ₇₀₂ is calculated in a similar way by replacing the coordinates of the sensor 70 ₁ by the coordinates of the sensor 70 ₂ .

Time t _a70 is then obtained by combining times tc ₇₀₁ and tc ₇₀₂ calculated for the different bands 62 on which a charge peak has been detected. For example, time t _a70 is the arithmetic mean of all times tc ₇₀₁ and tc ₇₀₂ calculated. When the instants t _a70 and t _a92 are both determined, the arrival instant t _a is obtained by combining these two instants t _a70 and t _a92 . For example, in a simple embodiment, time t _a is equal to the arithmetic mean of times t _a70 and t _a92 .

There figure 13 represents four conductive grids 220 to 223, capable of being used instead of the grid 8. The grids 220 to 223 here each extend in the same horizontal plane as the horizontal plane in which the grid 8 extends. grids 220 to 223 are arranged and arranged next to each other, so as to occupy the same surface as grid 8. Grids 220 to 223 are electrically insulated from each other. To this end, they are here electrically isolated from each other by two horizontal separations 226 and 228 parallel, respectively, to the X and Y directions. Thus, each grid 220 to 223 corresponds to a quarter disc. Each grid 220 to 223 is connected to a respective sensor 92. Here, gates 220 to 223 are connected to sensors 92a to 92d, respectively. For example, grids 220 to 223 are identical to grid 8, except that each of them occupies a respective part of the surface likely to be traversed by the first avalanche of secondary electrons. In particular, each of the gates 220 to 223 is connected to terminal 36.

The operation of a detector in which grid 8 is replaced by grids 220 to 223 is deduced from the explanations previously given. This detector is also capable of distinguishing, from the measurements of the sensors 92a to 92d, two elementary particles which arrive at the same time on the cathode 4, from the moment when each of these elementary particles triggers an avalanche of secondary electrons which pass through a respective one of grids 220 to 223.

There figure 14 represents a reading plate 250 identical to plate 16 except that the tiles 120 are replaced by tiles 252. The tiles 252 are identical to the tiles 120 except that they each have a triangular shape. More specifically, each tile 252 is an equilateral or isosceles triangle. In this embodiment, the tiles 252 are electrically connected to each other so as to form conductive strips 254 which extend parallel to six directions A, B, C, D, E and F. Directions A and D are parallel to the Y direction. The B and E directions are angularly offset by -60° from, respectively, to directions A and D. Directions C and E are angularly offset by +60° with respect to directions A and D, respectively.

On the figure 14 , the reference numerals 252a, 252b, 252c, 252d, 252e and 252f are used to designate the tiles 252 which belong to parallel conductive strips, respectively, to the directions A, B, C, D, E and F. To simplify the figure 14 , each tile that belongs to the conductive strips that extend parallel to a predetermined direction is filled with a respective texture, which makes it possible to identify this tile in the plate 250, even without a numerical reference. In the paving of the figure 14 , the periodically repeating pattern is a hexagon having one each of tiles 252a, 252b, 252c, 252d, 252e and 252f. In this pattern, these tiles 252a, 252b, 252c, 252d, 252e and 252f share a common vertex located on the geometric center of the hexagon. This hexagon is repeated periodically in directions A, B and C.

Tiles 252a and 252d are aligned along lines parallel to directions A and D such as line 256. Along line 256, a tile 252d is interposed between each pair of successive tiles 252a.

Tiles 252b and 252f are aligned along lines parallel to directions B and F such as line 258. Along line 258, a tile 252b is interposed between each pair of successive tiles 252f.

Tiles 252c and 252e are aligned along lines parallel to directions C and E such as line 260. Along line 260, a tile 252c is interposed between each pair of successive tiles 252e.

Thanks to this arrangement and this connection of the tiles 252 between them, each tile 252, which is not located on an edge of the paving, is immediately surrounded by tiles 252 belonging to five different conductive strips. Therefore, each point of impact results in a variation of the electrical charge of at least six different conductive strips. With the plate 250, it is therefore possible to determine, without ambiguity, the position of at least five simultaneous impact points if the distance separating these impact points two by two is greater than the largest dimension of the tile.

Chapter II. VARIANTS Variants of dynodes

Alternatively, matrix 34 is made of the same material as coating 32.

Many methods are possible to manufacture the coating 32. For example, the coating is obtained by a chemical reaction between the material that makes up the matrix 34 and a chemical reagent. For example, this chemical reagent is a liquid or gaseous reagent introduced inside each of the channels. For example, coating 32 is the result of oxidation or nitridation of matrix 34.

Other emissive materials can be used to make the coating 32. For example, the coating 32 can also be made in one or more of the materials selected from the group consisting of materials listed between lines 41 and 44 of column 10 of US6384519B1 .

In another embodiment, the coating 32 does not cover all of the channel walls. For example, the coating 32 is only located on the upper part of the channels, while the lower part of these channels has no emissive coating.

In another embodiment, the emissive material is a gas and the channels are filled with this gas. For example, the gas is a mixture of 90%, by mass, argon and 10%, by mass, carbon dioxide. In this case, coating 32 can be omitted.

The cross section of the channels can have any shape. For example, the cross section of the channels can be a polygon, such as a square, or be an oval.

The cross-section of the channels is not necessarily constant over the entire length of the channel. For example, the cross-section of the channel can be reduced as one advances towards its exit.

Many methods are possible to manufacture the channels. For example, the channels can be produced by anisotropic plasma etching, by photolithography or otherwise.

The axis of the channels can be tilted with respect to the horizontal plane. If the detector has several dynodes stacked one above the other, the axes of the channels of the upper dynode are preferably inclined along a first direction which intersects a second direction. The axes of the channels of the lower dynode are then parallel to this second direction.

In another embodiment, the channels do not extend along a straight axis, but along a curved or sinuous path.

The dynode can be made of other material. For example, as a variant, the dynode is made of a resistive or dielectric or conductive material. For example, the material used to make the dynode can be chosen from the group consisting of the materials listed between lines 6 and 17 of column 10 of US6384519B1 .

When the dynode is made of a dielectric material, the conductivity of the walls of the channels can be increased by depositing on these walls an underlayer of a resistive material such as, for example, a resistive polymer underlayer. This sub-layer then forms the wall of the channel on which the emissive coating is produced.

Variant of the reading plate

When the sensors 70 are connected between the ends of the conductive strips, it is not necessary for the ends of each conductive strip to be located on the edge of the reading plate. As a variant, the ends of at least some of the conductive strips are then located between the edges of the reading plate.

The conductive strips can be replaced by conductive electrodes electrically insulated from each other and individually connected each to its own sensor 70 as described in US6384519B1 .

Alternatively, the conductive strips are rectilinear strips which extend in a single plane. They therefore have no tiles located in a first horizontal plane and electrical connections located under this first horizontal plane. In this case, so that the conductive strips that extend in secant directions can cross each other, they are made in horizontal planes located at different heights.

As a variant, a full and uniform resistive layer is deposited on the outer face 60 of the plate 16. Optionally, this resistive layer is separated from the conductive strips 62 by a layer of dielectric material. The surface resistivity of this resistive layer, known by the English term “sheet resistivity” or “surface resistivity” at 20° Celsius is between 10 kΩ/square and 100 MΩ/square. Preferably, the surface resistivity is greater than 100 kΩ/square or 1 MΩ/square and, advantageously, less than 10 MΩ/square. By capacitive coupling between this resistive layer and the strips 62, the secondary electrons received on the resistive layer generate a corresponding variation in the electrical charge of some of the strips 62. It is this variation in the electrical charge of the strips 62 which is measured by the sensors 70. This resistive layer makes it possible to spread the electrical charges on the outer face 60.

In another variant, the substrate 61 additionally comprises ground planes extending horizontally between the metallization layers to reduce the crosstalk between the conductive strips.

Other detector variants

Elementary particles other than a photon can be detected. For example, the elementary particle to be detected can be a charged particle, such as an ion or a muon, or a neutral particle such as a neutron. For this, the cathode is then made of an emissive material which releases at least one electron when it is struck by the elementary particle to be detected. The emissive material therefore depends on the elementary particle to be detected. For example, to detect a neutron, the emissive material used can be boron or palladium. It is also possible to detect protons by choosing the appropriate emissive material.

As a variant, the detector comprises a single dynode and a single conductive grid.

As a variant, a spacer can also be placed between the dynodes 6 and 10. This makes it possible in particular to improve the spatial dispersion of the secondary electrons in different channels. For example, it is then possible to distribute the electrons which leave the outlet 30 of a single channel 24 in several channels 40 even if the diameter Dm40 of the channels 40 is greater than the diameter Dm24. Conversely, the spacer 14 can be omitted in certain embodiments such as the embodiments where the diameter Dm24 is greater than the diameter Dm40.

In a simplified embodiment, the detector comprises a single sensor 92. In this case, the combination of instants tc _92a to tc _92d is omitted.

There are many different technologies for measuring a load peak such as peak 64 or 94. In particular, a capacitive or inductive measurement can be implemented. In these cases, the sensors 70 and 92 are not necessarily electrically connected directly to, respectively, a strip 62 and the grid 8.

When the detector comprises several dynodes and several conductive grids located between these dynodes, only one or more of these conductive grids are connected to sensors 92. For example, in an alternative embodiment, the sensors 92 are connected to the grid 12 at the instead of being connected to the grid 8. In this case, the quantity of electric charges which crosses the grid 12 is greater but the spatial distribution of the electrons is then more spread out.

Other embodiments of grids 220 to 223 are possible. For example, more than four grids can be used or, conversely, less than four grids. The shapes of the grids 220 to 223 can also be different.

As a variant, the sensors 70 are connected to the distal or proximal end of the conductive strips 62. In this case, the connections to the strips 62 are distributed over the periphery of the reading plate. It is then not necessary to provide a vertical via to connect the sensors 70 to a central point of these strips 62.

Variants of the operating method

Alternatively, during operation 210, location P702 is not determined. For example, in this case, the Pf position of the point of impact is only established from the location P701.

In another variant, the location P701 is not determined. For example, in this case, the position Pf is established using only the location P702 and without using the points of intersection between the conductive strips 62. In this case, it is not necessary for the conductive strips to cross. For example, they can all be parallel to each other.

Enabling and, alternately, disabling of location P701 can be applied to location P702. In another embodiment, enabling and, alternately, disabling of the location determined from the measurements of the sensors 92 may be omitted.

During operation 156, it is also possible to determine a location P92 where the first avalanche crosses the grid 8 from the measurements of the sensors 92. More precisely, the fact that there are several sensors is exploited at this time. 92 connected to the same grid 8 at different places. The propagation times of the electric signal, generated by the first avalanche of secondary electrons which crosses the grid 8, up to each of the sensors 92a to 92d are then not identical because the distances to be covered are not the same. It is this difference between propagation times which is exploited to determine the P92 location by triangulation. The determination of a location by triangulation being well known, this is not described in more detail here. Then, the position Pf of the point of impact is established by combining the locations P701 and P92 or P702 and P92. For example, position Pf is equal to the arithmetic mean of locations P701 and P92.

There are many ways to combine locations P701, P702 and P92 to determine the Pf position of the point of impact. For example, a weighted average of locations P701 and P92 can be used, preferably giving more weight to location P701.

The determination of the instant t _a92 from the various corrected instants tc _92a to tc _92d can be carried out other than by a simple arithmetic average. For example, the arithmetic average is replaced by a weighted average in which a greater weight is assigned to the sensors 92 which are closest to the point of impact. In another embodiment, only the measurement or measurements of the sensors 92 which are at a distance less than a predetermined threshold from the point of impact are taken into account. Similarly, time t _a70 can be calculated by implementing means other than a simple arithmetic average. For example, the various variants described in the particular case of the determination of the instant t _a92 also apply to the determination of the instant t _a70 .

Other embodiments than an arithmetic mean of times t _a70 and t _a92 are possible to establish time t _a . For example, time t _a is a weighted average of times t _a70 and t _a92 giving more weight to time t _a92 than to time t _a70 .

In a simplified embodiment, the correction of times tm ₉₂ or tm ₇₀ is omitted. For example, the instant t _a92 or t _a70 is calculated directly from the measurements of the sensors 92 or 70 but without using the position Pf of the point of impact. This embodiment is practical if the propagation times are negligible.

The calculation of time t _a70 can be implemented even if a single sensor 70 is connected to each conductive strip 62.

In a variant, the instant t _a70 is not determined and the measurements of the sensors 70 are not used to determine the instant t _a .

Alternatively, time t _a92 is not determined. For example, the instant t _a is determined solely from the measurements of the sensors 70. By way of illustration, the instant t _a is then taken equal to the instant t _a70 . In this case, the sensors 92 can be omitted.

Chapter III. ADVANTAGES OF THE EMBODIMENTS DESCRIBED

After crossing the conductive grid, the avalanche of secondary electrons flares up. The zone of impact of the secondary electrons on the reading plate is therefore wider than the zone of the conductive grid crossed by these same secondary electrons. In other words, the spatial dispersion of these secondary electrons is lower at the level of the conductive grid than at the level of the reading plate. Since the spatial dispersion of these secondary electrons at the level of the conductive grid is lower, it generates a narrower charge peak. In addition, the impedance of the conductive grid is much more uniform than the impedance of the conductive strips 62. Indeed, the impedance of the tiles 120 is different from the impedance of the connections 128 which creates numerous impedance breaks along each strip 62. Because of these two characteristics, the uncertainty on the instant t _a at which the elementary particle arrives is lower if this instant is established from the measurements of the sensors 92 than only from the measurements of the sensors 70.

The fact of using the corrected instants tc _92a to tc _92d makes it possible to further increase the precision on the measurement of the instant t _a of arrival.

The fact of using several sensors 92 also makes it possible to further increase the precision on the measurement of the instant t _a of arrival.

The fact of using several grids contiguous to each other in the same plane makes it possible to distinguish several elementary particles touching the cathode 4 simultaneously. This then makes it possible to determine more reliably the time of arrival t _a of these elementary particles.

Using conductive strips instead of individual electrodes greatly reduces the number of sensors 70 needed to determine the position Pf of the point of impact. In addition, the tiles of each conductive strip are located in the same plane, so that they have the same sensitivity. It is therefore not necessary to implement means for correcting differences in sensitivity between the conductive strips, as is the case when these conductive strips are located in different horizontal planes.

The fact that the largest dimension of the tiles is less than or equal to the largest dimension of the exit of the channels simply makes it possible to distribute the avalanche of secondary electrons over several tiles and this even in the case where the detector comprises a single dynode .

The fact of connecting the sensor 70 not to the ends of the strip 62, but at a central point, passing through the intermediary of the via 136, makes it possible to house the sensors 70 under the strip 62. This facilitates the placement of the sensors 70 and therefore the manufacture of the reading plate.

The fact that the output of the channels of the dynode 6 at least partially covers several inputs of the dynode 10 makes it possible to simply spread the avalanche of secondary electrons over a greater number of tiles, even if the largest dimension of these tiles is greater than the largest dimension of the cross-section of the outlet of the channels directly opposite these tiles. This makes it possible to simplify the design and manufacture of the reading plate, since the constraints on the dimensions of the tiles are reduced.

The fact that the cross section of the inlets 42 of the channels 40 of the lower dynode 10 are smaller than the cross section of the outlets 30 of the channels 24 of the dynode 6 simply allows the avalanche of electrons to be spread secondary. In particular, this spreading occurs without it being necessary for this to precisely position the dynode 6 with respect to the dynode 10.

The invention naturally applies to the study of particle physics. The invention also applies to the field of imaging, in particular in the space, medical or environmental field and also the field of transport. For example, in the medical field, the invention can be used in the context of treatment by hadrontherapy or protontherapy or even in the context of positron emission therapy (PET).

Claims (11)

1. An elementary particle detector, this detector comprising:

   - a cathode (4) and a conducting grid (8, 12) able to create a potential difference able to accelerate electrons in the direction of the conducting grid, the conducting grid being able to be traversed by the accelerated electrons,

   - a dynode (6, 10) interposed between the cathode and the conducting grid, this dynode being able, for each elementary particle, to produce an avalanche of secondary electrons, this dynode comprising for this purpose several channels, each channel comprising an emissive material, this emissive material being capable, in response to an impact of an electron, of generating, on average, more than one secondary electron,

   - a reader plate (16; 200) arranged on the side of the conducting grid opposite to the dynode, this reader plate comprising:

   • an external face (60) arranged in such a manner as to be impacted by the avalanche of secondary electrons, and

   • electrodes (120; 252) arranged next to one another in a face parallel to or coincident with the external face,

   - first sensors (70) able to measure the quantity of electrical charges on the electrodes,

   - a processing unit (80) capable of determining the location of the avalanche of electrons based on the quantity of electrical charges measured by the first sensors and on the known location of the electrodes,

   characterized in that:

   - the detector comprises at least a second sensor (92), each second sensor being able to measure an electrical signal produced by the secondary electrons when they pass through the conducting grid, and

   - the processing unit (80) is capable, in addition, of establishing a time of arrival of the elementary particle based on a time referred to as "crossing time" where the electrical signal is measured by the second sensor.
2. The detector according to claim 1, in which the processing unit (80) is configured for:

   - correcting the crossing time by subtracting from it a time for propagation of the electrical signal between the location where the conducting grid (8, 12) is traversed by the avalanche of secondary electrons and the location where the electrical signal is measured by the second sensor (92), the location where the conducting grid is traversed by the avalanche of secondary electrons being established based on the measurements from the first sensors (70), then

   - determining the time of arrival based on the corrected crossing time thus obtained.
3. The detector according to claim 2, in which the detector comprises several second sensors (92a-92d) situated at respective locations, spaced out from one another, and the processing unit (80) is configured for determining the time of arrival using the corrected crossing times obtained based on the measurements from each of these second sensors (92).
4. The detector according to any one of the preceding claims, in which the detector comprises:

   - several grids (220-223) arranged so as to be contiguous with one another in the same plane in order to cover the whole surface area able to be traversed by the avalanche of secondary electrons, these conducting grids being electrically isolated from one another, and

   - at least a second sensor (92a-92d) associated with each of these conducting grids for measuring the electrical signal only in this conducting grid.
5. The detector according to any one of the preceding claims, in which the reader plate comprises, in the order starting from its external face:

   - a dielectric layer (104, 108, 112) having a front face turned toward the external face,

   - conducting strips (62) forming the electrodes of the reader plate, these conducting strips extending mainly parallel to the front face in at least two different directions, each conducting strip being electrically connected to at least a first electrical charge sensor (70), these conducting strips being formed by:

   • conducting tiles (120; 252) all identical to one another and all situated at the same distance from the external face, these conducting tiles being distributed over the front face of the dielectric layer and being mechanically separated from one another by a dielectric material, and

   • electrical connections (128), situated under the dielectric layer, which electrically connect conducting tiles in series in such a manner as to form said conducting strips, these electrical connections being arranged in such a manner that each conducting tile belongs to a single conducting strip and each side of a tile is adjacent to the side of another tile belonging to another conducting strip.
6. The detector according to claim 5, in which the largest dimension of each tile (120; 252) is less than or equal to the largest dimension of the transverse cross section of the exit (44) of each channel (40) directly facing the reader plate, the largest dimension of the transverse cross section of the exit of a channel and the largest dimension of a tile being equal to the length of the largest side of the rectangle with the smallest surface area which respectively entirely contains this transverse cross section and this tile.
7. The detector according to claim 5 or 6, in which:

   - at least one conducting strip (62) extends from a first end to a second end, and

   - the reader plate comprises at least one via (136) which extends perpendicularly to its external face from a point situated between the ends of the conducting strip up to a point of electrical connection to a first sensor (70).
8. The detector according to any one of claims 5 to 7, in which the detector comprises at least one upper dynode (6) stacked onto a lower dynode (10), the lower dynode being arranged with respect to the upper dynode in such a manner that the secondary electrons coming out of a channel of the upper dynode are distributed into several channels of the lower dynode.
9. The detector according to claim 8, in which the diameter of the transverse cross section of the entries (42) to the channels of the lower dynode is equal to or less than the diameter of the transverse cross section of the exits (30) from the channels of the upper dynode.
10. A method for detecting an elementary particle by means of a detector according to any one of the preceding claims, in which the method comprises:

    - the measurement (152) of the quantity of electrical charges received by each electrode of the reader plate by means of the first sensors, and

    - the determination (156; 210) of the location of the avalanche of secondary electrons based on the quantity of electrical charges measured by the first sensors and based on the known location of the electrodes,

    characterized in that the method additionally comprises:

    - the measurement (152) of an electrical signal produced by the secondary electrons when they pass through the conducting grid by means of said at least one second sensor (92), and

    - the establishment (158; 212) of a time of arrival of the elementary particle based on a time referred to as "crossing time" when the electrical signal is measured by the second sensor.
11. An information recording medium (82), readable by an electronic computer, characterized in that this information recording medium comprises instructions for the execution of a method according to claim 10, when these instructions are executed by the electronic computer.

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