EP1343194A1 - Radiation detectors and autoradiographic imaging devices comprising such detectors - Google Patents

Abstract

The detector (1) merges the conversion and amplification spaces by combining the cathode with an entry electrode (8). The entry electrode is separated from the output grid (9) by insulated spacers (11) and fields (E2,E3) propel electrons initiated by ionizing particles (I) from the sample (S) through the neon and isobutane quenching gas towards a segmented anode (6) which is connected to a processor (21).

Description

The present invention relates to radiation detectors and to autoradiographic imaging devices comprising such detectors.

• une enceinte contenant un milieu adapté pour générer des électrons sous l'effet de radiations,
• un espace de conversion dans lequel les radiations génèrent des électrons, cet espace de conversion comportant une cathode par laquelle pénètrent les radiations à détecter,
• une anode pour générer des signaux en fonction d'un courant généré par le déplacement de charges au voisinage de cette anode, ces charges correspondant à des électrons et des ions dont les radiations sont directement ou indirectement à l'origine,
• des moyens de polarisation générant un champ électrique adapté pour entraîner des électrons dans la direction allant de la cathode vers l'anode,
• au moins une structure amplificatrice, située entre la cathode et l'anode, chaque structure amplificatrice comprenant une électrode d'entrée et une électrode de sortie, maintenues séparées par une entretoise isolante comportant au moins un espace d'amplification des électrons dans lequel des électrons sont générés par avalanche à partir des électrons générés par les radiations, chaque espace d'amplification présentant des dimensions latérales, dans un plan perpendiculaire au champ électrique, supérieures à la distance séparant les électrodes d'entrée et de sortie, et chaque espace d'amplification débouchant sur au moins une ouverture de l'électrode de sortie, pour laisser passer au moins une partie des électrons générés par avalanche.

More particularly, the invention relates to an ionizing radiation detector comprising:

• an enclosure containing a medium suitable for generating electrons under the effect of radiation,
• a conversion space into which the radiations generate electrons, this conversion space comprising a cathode through which the radiations to be detected penetrate,
• an anode for generating signals as a function of a current generated by the displacement of charges in the vicinity of this anode, these charges corresponding to electrons and ions whose radiations are directly or indirectly at the origin,
• polarization means generating an electric field adapted to drive electrons in the direction going from the cathode towards the anode,
• at least one amplifying structure, located between the cathode and the anode, each amplifying structure comprising an input electrode and an output electrode, kept separated by an insulating spacer comprising at least one electron amplification space in which electrons are generated by avalanche from electrons generated by radiation, each amplification space having lateral dimensions, in a plane perpendicular to the electric field, greater than the distance separating the input and output electrodes, and each space amplification opening on at least one opening of the output electrode, to allow at least part of the electrons generated by avalanche to pass.

The aim of the present invention is in particular to optimize the spatial resolution and / or the gain of this type of detector while retaining good operating stability.

To this end, according to the invention, a detector of the kind in question is characterized in that the lateral dimensions of each amplification space are greater than the dimensions, in a plane perpendicular to the electric field, of each opening of the electrode output on which this amplification space leads.

Thanks to these provisions, the dead zones due to the presence of the insulating spacer are greatly reduced. Consequently, the field is much more uniform in each amplification space and in the vicinity of the conversion space. Thus, the detectors according to the invention have better spatial resolution and a higher gain than the detectors of the prior art, and nevertheless retain excellent operating stability. This stability is possible even with input and output electrodes made up of very thin grids, of the order of only a few microns. The exploitation of the electrical properties of thin grids even contributes to this stability. Thanks to this stability, it is possible to have a significant amplification, up to a factor of one hundred thousand, which facilitates the detection and localization of the radiation penetrating into this detector. Thanks to this stability, it is also possible to eliminate a large part of the insulating masses necessary for the separation of the input and output electrodes.

Thus, in the detector according to the invention, the spacer is adapted to provide, opposite each opening of the output electrode, an amplification space whose section perpendicular to the electric field is much greater than the section of this opening. The insulation constituting the spacer therefore does not close the space located opposite this opening. The electric field generated by the input and output electrodes is thus practically not deformed. This makes it possible, in particular, to obtain images of very large objects, for example 7 centimeters, while eliminating most of the masking effects linked to the presence of a spacer.

The information collected at the anode is therefore a more representative image of the source of ionizing radiation, thus increasing the spatial resolution of this type of detector. The detector according to the invention makes it possible, for example, to obtain a spatial precision of around ten microns on surfaces of 50 × 50 cm ² .

• l'électrode d'entrée, l'électrode de sortie et l'entretoise sont respectivement constituées d'éléments indépendants et adaptés pour être désolidarisés ; ce qui permet une optimisation de chacun de ces éléments, indépendamment les uns des autres, et donne la possibilité d'utiliser, pour réaliser chacun de ces éléments, une technique appropriée optimisée et/ou économique, etc. ;
• l'entretoise est constituée d'une plaque de matériau isolant sensiblement perpendiculaire localement au champ électrique, percée de part en part, dans la direction parallèle au champ électrique, d'au moins une fenêtre ouverte à la fois sur l'électrode d'entrée et sur l'électrode de sortie, chaque fenêtre délimitant un espace d'amplification ayant une dimension D perpendiculairement au champ électrique satisfaisant à :
  

où

• y
  
  est la flèche au centre de chaque espace d'amplification,
• E est le module d'Young du matériau constituant la grille d'entrée ou de sortie,
• I est le moment quadratique d'une portion de la grille d'entrée ou de sortie, correspondant aux dimensions de chaque espace d'amplification,
• N est la précontrainte en tension de la grille d'entrée ou de sortie, et
• ρ est la charge linéique électrostatique de l'électrode d'entrée ou de sortie,

   ρ étant donnée par : $${\text{ρ = [ε}}_{\text{0}}{\text{<figure-callout id="2" label="ε r U" filenames="imgf0004.png,imgf0007.png" state="{{state}}">ε</figure-callout>}}_{\text{r}}\frac{{\mathit{\text{U}}}^{}}{}\frac{{}^{\text{2}}}{\text{2}{\mathit{\text{e}}}^{\text{2}}}\text{].}\frac{\mathit{\text{S}}}{\text{2}\mathit{\text{l}}}\text{,}$$

où

• U est la tension appliquée entre les grilles d'entrée et de sortie,
• ε₀ et ε_r sont respectivement les permittivités du vide et relative du milieu,
• e est l'épaisseur de l'entretoise, et
• S est la surface de la grille d'entrée ou de sortie couvrant chaque espace d'amplification ; cette disposition permet d'optimiser la transparence de l'entretoise, sans altérer le gain de la structure amplificatrice et facilite l'assemblage de la structure amplificatrice, par rapport à l'utilisation d'une entretoise constituée de billes ou de fibres indépendantes les unes des autres ; dans le cas où l'entretoise ne comporte qu'une fenêtre, il n'y a pas du tout de zones mortes ;
• l'entretoise comporte au moins deux fenêtres séparées l'une de l'autre par un barreau dont l'épaisseur entre ces deux fenêtres est inférieure ou égale à la dimension de ce barreau parallèlement au champ électrique, qui est elle-même inférieure ou égale à 500 microns ; une telle entretoise présente l'avantage de limiter les zones mortes ; néanmoins, cette disposition n'est pas limitative et il est possible de concevoir, sans sortir du cadre de l'invention, des détecteurs dans lesquels l'épaisseur d'un barreau entre deux fenêtres peut être supérieure ou égale à l'épaisseur de ce barreau parallèlement au champ électrique ;
• il comporte une structure amplificatrice pour laquelle l'espace d'amplification est confondu avec l'espace de conversion, l'électrode d'entrée de cette structure amplificatrice correspondant à la cathode ; ceci permet de réduire fortement les effets de parallaxe et de s'affranchir des effets de trajectoire des particules chargées incidentes, y compris pour les particules chargées émises par les marqueurs classiquement utilisés en biologie ; ainsi, la position des points d'émission, quels que soient les isotopes à l'origine de cette émission, peut être déterminée très précisément ; dans ce cas, l'électrode d'entrée est avantageusement formée d'une face au moins partiellement conductrice d'un échantillon émetteur de radiations ionisantes ; ces dispositions sont particulièrement avantageuses lorsque la source de radiations ionisantes n'est pas collimatée, et plus particulièrement encore pour l'autoradiographie de particules bêta;
• il comprend plusieurs structures amplificatrices empilées, entre la cathode et l'anode, dans la direction du champ électrique ; l'électrode de sortie d'une première structure amplificatrice est confondue avec l'électrode d'entrée d'une deuxième structure amplificatrice disposée entre la première structure amplificatrice et l'anode ; dans ces cas, au moins deux structures amplificatrices ont éventuellement des géométries différentes ; et
• il comprend un espace d'étalement situé entre l'anode et l'électrode de sortie en regard de l'anode, et dans lequel règne un champ électrique adapté (avantageusement inférieur à 10 kV/cm) à un étalement, dans des directions perpendiculaires à ce champ, des électrons par diffusion sur les atomes et molécules du milieu contenu dans l'enceinte.

In preferred embodiments of the invention, it is possible optionally to have recourse to one and / or the other of the following arrangements:

• the input electrode, the output electrode and the spacer respectively consist of independent elements and adapted to be separated; which allows an optimization of each of these elements, independently of each other, and gives the possibility of using, to produce each of these elements, an appropriate optimized and / or economical technique, etc. ;
• the spacer consists of a plate of insulating material substantially perpendicular locally to the electric field, pierced right through, in the direction parallel to the electric field, of at least one window open both on the input electrode and on the output electrode, each window delimiting an amplification space having a dimension D perpendicular to the electric field satisfying:
  

or

• there
  
  is the arrow in the center of each amplification space,
• E is the Young's modulus of the material constituting the input or output grid,
• I is the quadratic moment of a portion of the input or output grid, corresponding to the dimensions of each amplification space,
• N is the voltage preload of the input or output grid, and
• ρ is the linear electrostatic charge of the input or output electrode,

ρ being given by: $${\text{ρ = [ε}}_{\text{0}}{\text{<figure-callout id="2" label="ε r U" filenames="imgf0004.png,imgf0007.png" state="{{state}}">ε </figure-callout>}}_{\text{r}}\frac{{\mathit{\text{U}}}^{}}{}\frac{{}^{\text{2}}}{\text{2}{\mathit{\text{e}}}^{\text{2}}}\text{].}\frac{\mathit{\text{S}}}{\text{2}\mathit{\text{l}}}\text{,}$$

or

• U is the voltage applied between the input and output grids,
• ε ₀ and ε _r are respectively the permittivities of the vacuum and relative of the medium,
• e is the thickness of the spacer, and
• S is the area of the input or output grid covering each amplification space; this arrangement optimizes the transparency of the spacer, without altering the gain of the amplifying structure and facilitates the assembly of the amplifying structure, compared to the use of a spacer consisting of balls or fibers independent of each other; in the case where the spacer has only one window, there are no dead zones at all;
• the spacer comprises at least two windows separated from each other by a bar whose thickness between these two windows is less than or equal to the dimension of this bar parallel to the electric field, which is itself less or equal at 500 microns; such a spacer has the advantage of limiting dead zones; however, this provision is not limiting and it is possible to design, without departing from the scope of the invention, detectors in which the thickness of a bar between two windows can be greater than or equal to the thickness of this bar parallel to the electric field;
• it comprises an amplifying structure for which the amplification space is merged with the conversion space, the input electrode of this amplifying structure corresponding to the cathode; this makes it possible to greatly reduce the parallax effects and to overcome the trajectory effects of the incident charged particles, including for the charged particles emitted by the markers conventionally used in biology; thus, the position of the emission points, whatever the isotopes at the origin of this emission, can be determined very precisely; in this case, the input electrode is advantageously formed from an at least partially conductive face of a sample emitting ionizing radiation; these provisions are particularly advantageous when the source of ionizing radiation is not collimated, and more particularly for autoradiography of beta particles;
• it comprises several stacking amplifying structures, between the cathode and the anode, in the direction of the electric field; the output electrode of a first amplifying structure is merged with the input electrode of a second amplifying structure disposed between the first amplifying structure and the anode; in these cases, at least two amplifying structures may have different geometries; and
• it includes a spreading space located between the anode and the output electrode facing the anode, and in which an electric field prevails (advantageously less than 10 kV / cm) for spreading, in perpendicular directions in this field, electrons by diffusion on the atoms and molecules of the medium contained in the enclosure.

The detectors according to the invention comprising several stacking amplifying structures are very clearly distinguished from detectors of the type of those of the prior art comprising a stack of insulating plates, the two main faces of which are covered with a conductive material, which are pierced with openings and which are subjected to a potential difference at the origin of an electric field responsible for an avalanche multiplication in openings made in these plates. In fact, in the detectors according to the invention, it is possible to make a judicious choice of the proper electrical properties of the input and output electrodes, as well as the electric fields which prevail on each side of the conductive surfaces of each amplifying structure. . We can thus separate the different amplifying structures, in the direction perpendicular to the electric field, by distances which can be up to a thousand times greater than the distance which usually separates the openings of the plates pierced with detectors of the prior art, while retaining excellent electrical stability (relative uniformity of the electric field between spacers separated by considerable distances from the distance separating the input and output electrodes of the same amplifying structure) and excellent mechanical stability (reduced deformation of the input and output electrodes including the thickness is only a few microns).

Thanks to these arrangements, the detector according to the invention makes it possible to produce numerous structures, for various applications, with successive electron amplifier spaces, in which the introduction of material is very reduced, compared to the state of the presently known art. The effects of parasitic shadow or reduction of the spatial resolution coming from this material are thus very greatly reduced.

Advantageously, the input and output electrodes of the amplifying structure of the detector according to the invention consist of grids whose thickness, parallel to the general direction of the electric field between the anode and the cathode, is much less than the dimensions lateral openings of these grills, that is to say in a plane perpendicular to this electric field. Thanks to this arrangement, it is possible to choose the parameters of the electric fields between the different electrodes, so that the lines of force on each of the faces of a grid, create on this grid forces which balance each other at least in part. The thinness of the grids also limits the fraction of field lines which lead to the side walls of the openings in the grids and which therefore cannot contribute to the balancing of the grids. All this contributes to the stability of this grid and therefore to the parallelism of the input and output electrodes. It is thus possible to limit the mass of insulating material constituting the spacer between the input and output electrodes.

By these arrangements, the detector according to the invention is clearly distinguished from those of the prior art in which the input and output electrodes consist of thick grids, relative to the distance which separates them, or in which the electrodes inlet and outlet are deposited on thick insulation and drilled with holes.

According to another aspect, the invention relates to a autoradiographic imaging device comprising a detector comprising one and / or the other of the characteristics indicated above and further comprising a sample holder adapted so that this detector is placed at least 50 microns of a sample emitting ionizing radiation, mounted on the sample holder.

• l'électrode d'entrée est constituée par un échantillon au moins partiellement conducteur disposé sur le porte-échantillon ;
• l'anode est transparente aux signaux optiques, ce dispositif comprenant en outre un dispositif de lecture optique de ces signaux ; et
• l'anode comporte une pluralité d'anodes élémentaires reliées à au moins une voie de lecture par des pistes, chaque voie de lecture étant reliée à plusieurs anodes élémentaires.

Advantageously, this imaging device includes one and / or the other of the following provisions:

• the input electrode consists of an at least partially conductive sample placed on the sample holder;
• the anode is transparent to optical signals, this device further comprising a device for optical reading of these signals; and
• the anode comprises a plurality of elementary anodes connected to at least one reading channel by tracks, each reading channel being connected to several elementary anodes.

Other aspects, aims and advantages of the invention will appear on reading the description of several of its embodiments.

• la figure 1 est une coupe schématique, perpendiculaire à ses faces principales, d'un premier mode de réalisation du détecteur selon l'invention,
• la figure 2 est une coupe schématique, dans un plan analogue à celui de la figure 1, d'une partie de la structure amplificatrice du détecteur représenté sur la figure 1,
• la figure 3 est une coupe schématique, dans un plan analogue à celui des figures 1 et 2, d'une partie de l'anode du détecteur représenté sur la figure 1,
• la figure 4 représente schématiquement en perspective les pavés constitutifs de l'anode représentée sur la figure 3,
• la figure 5 représente schématiquement vu de dessus, l'agencement des pistes croisées de l'anode représentée sur les figures 3 et 4,
• la figure 6 représente schématiquement le mode de connexion des pavés aux pistes de l'anode représentée sur les figures 3, 4 et 5,
• la figure 7 est une coupe schématique, selon un plan analogue à celui de la figure 1, d'un deuxième mode de réalisation du dispositif selon l'invention,
• la figure 8 est une coupe schématique, selon un plan analogue à celui des figures 1 et 7, d'un troisième mode de réalisation du détecteur selon l'invention,
• la figure 9 est une coupe schématique, selon un plan analogue à celui des figures 1, 7 et 8, d'un quatrième mode de réalisation du détecteur selon l'invention,
• la figure 10 représente schématiquement en perspective un cinquième mode de réalisation du détecteur selon l'invention, et
• la figure 11 représente schématiquement en perspective un dispositif d'imagerie autoradiographique comprenant le détecteur représenté sur la figure 10.

The invention will also be better understood using the drawings, in which:

• FIG. 1 is a schematic section, perpendicular to its main faces, of a first embodiment of the detector according to the invention,
• FIG. 2 is a schematic section, in a plane similar to that of FIG. 1, of a part of the amplifying structure of the detector shown in FIG. 1,
• FIG. 3 is a schematic section, in a plane similar to that of FIGS. 1 and 2, of a part of the anode of the detector shown in FIG. 1,
• FIG. 4 schematically represents in perspective the blocks constituting the anode shown in FIG. 3,
• FIG. 5 schematically shows, seen from above, the arrangement of the crossed tracks of the anode shown in FIGS. 3 and 4,
• FIG. 6 schematically represents the method of connecting the blocks to the tracks of the anode shown in FIGS. 3, 4 and 5,
• FIG. 7 is a schematic section, along a plane similar to that of FIG. 1, of a second embodiment of the device according to the invention,
• FIG. 8 is a diagrammatic section along a plane similar to that of FIGS. 1 and 7, of a third embodiment of the detector according to the invention,
• FIG. 9 is a diagrammatic section along a plane similar to that of FIGS. 1, 7 and 8, of a fourth embodiment of the detector according to the invention,
• FIG. 10 schematically represents in perspective a fifth embodiment of the detector according to the invention, and
• FIG. 11 schematically represents in perspective a autoradiographic imaging device comprising the detector represented in FIG. 10.

In the various figures, the same references designate identical or similar elements.

Five embodiments of the detector 1 according to the invention are described below.

According to the first embodiment, shown in Figure 1, the detector 1 comprises a flattened enclosure 2 with two main faces 2a and 2b opposite and parallel to each other. This enclosure 2 contains a medium suitable for emitting primary electrons under the effect of ionizing radiation emitted by a sample S placed near one 2a of the main faces 2a, 2b of the enclosure 2. Advantageously, this medium is constituted of a gas circulating between an inlet 3 and an outlet 4.

This gas consists of a mixture comprising a noble gas and organic molecules. These organic molecules are intended to control the amplification process by avalanche. They are known to those skilled in the art under the Anglo-Saxon expression "quencher".

The gas circulating in the enclosure 2 is chosen as a function of the application for which the detector 1 is intended, that is to say as a function of the particles to be detected, of the reading mode, of the detection electronics, etc.

In the particular case of the detection of beta particles, this gas is advantageously at atmospheric pressure (for reasons of safety and economy) and comprises a noble gas whose electronic density mean is close to 10 electrons per atom, as is the case with neon. When the neon is used, the "quencher" advantageously consists of isobutane, present in the gas mixture up to a few percent of the number of molecules in this mixture.

The enclosure 2 contains a cathode 5, an anode 6 and an amplifying structure 7.

In the embodiment described here, the cathode 5, the anode 6 and the amplifying structure 7 are mutually parallel and parallel to the two main faces 2a, 2b of the enclosure 2.

The anode 6 is located near the face 2b opposite that 2a near which is the sample S.

The amplifier structure 7 is located between the cathode 5 and the anode 6. The space of the enclosure 2, located between the cathode 5 and the amplifier structure 7, constitutes a conversion space C. The ionizing radiation emitted by the sample S enter the conversion space C via cathode 5.

The space of the enclosure 2 located between the amplifying structure 7 and the anode 6 constitutes a spreading space E.

The amplifying structure 7 comprises an input electrode 8 and an output electrode 9, parallel to the cathode 5 and to the anode 6 and delimiting an amplification stage A.

Polarization means 10 are connected to the cathode 5, to the anode 6 and to the input 8 and output 9 electrodes. They make it possible to bring the cathode 5 to a potential HV1 / the anode 6 to a potential HV2, the input electrode at a potential HV3 and the output electrode at a potential HV4, these potentials responding to the inequality HV2>HV4>HV3> HV1.

• les électrodes d'entrée 8 et de sortie 9 sont espacées de 125 microns,
• les espaces de conversion C et d'étalement E ont une dimension, perpendiculairement aux électrodes d'entrée 8 et de sortie 9, sensiblement respectivement égales à 3 et 4 millimètres,
• l'anode 6 est mise à la masse,
• la cathode 5 est portée à un potentiel HV1 négatif sensiblement égal à -3000 volts,
• l'électrode d'entrée 8 est portée à un potentiel HV3 négatif sensiblement égal à -2100 volts, et
• l'électrode de sortie 9 est portée à un potentiel HV4 négatif sensiblement égal à -1600 volts.

In the embodiment described here,

• the input 8 and output 9 electrodes are spaced 125 microns apart,
• the conversion C and spreading E spaces have a dimension, perpendicular to the input 8 and output 9 electrodes, substantially equal to 3 and 4 millimeters respectively,
• anode 6 is earthed,
• cathode 5 is brought to a negative HV1 potential substantially equal to -3000 volts,
• the input electrode 8 is brought to a negative potential HV3 substantially equal to -2100 volts, and
• the output electrode 9 is brought to a negative potential HV4 substantially equal to -1600 volts.

The polarization means 10 thus make it possible to create electric fields E1, E2 and E3 respectively in the conversion space C, in the amplification stage A and in the spreading space E. The polarization means 10 cause the electrons from cathode 5, towards anode 6.

The cathode 5 consists of a thin electrically conductive plate pierced with small openings. Its thickness is advantageously substantially equal to 5 microns. It advantageously has a number of openings per linear inch of 200 LPI (Lines per inch).

It can optionally also consist of a woven grid (less expensive than the previous one), a sheet of metallized Mylar®, a sheet of unpierced metal (for example copper 10 microns thick), d '' a copper-colored adhesive tape stuck on a glass slide with an electrically conductive glue (for applications such as autoradiography, for example), a photocathode (possibly coupled with a detector Cerenkov), etc.

In the amplifying structure 7, shown in FIG. 2, the input electrode 8 and the output electrode 9 are separated by a spacer 11. The input electrode 8, the output electrode 9 and the spacer 11 are made up of independent elements which can be machined separately from each other. They are assembled and held together in the amplifying structure 7, but can be easily separated from each other, to be changed for example.

The input 8 and output 9 electrodes each consist respectively of a thin electrically conductive plate, of small thickness and pierced with small openings 12. By way of example, the openings 12 have the shape of a square of 39 microns on a side spaced from one another with a pitch p of 50 microns, which corresponds substantially to a number of openings 12 per linear inch of 500 LPI. It is also possible to use input 8 and output 9 electrodes of 2500 LPI, which corresponds substantially to 8 micron openings spaced 10 microns apart. Such input 8 and output 9 electrodes each form a grid which, given the small size of the openings 12, can be called a "micro-grid". Such micro-grids have already been described, for example, in document EP 855086.

The spacer 11 consists of a grid formed of an insulating material whose dielectric permittivity is between 2 and 5. This grid consists for example of a Kapton® plate having a thickness e advantageously less than 500 microns and preferably less than 300 microns, pierced with square windows 13 cut by laser or by chemical attack and separated by bars 14. In the structure amplifier 7, when the input electrode 8, the output electrode 9 and the spacer 11 are assembled, the windows 13 are open on the input electrode 8 and the output electrode 9. However, the respective openings 12 of the input 8 and output 9 electrodes are not necessarily aligned, in the direction of the electric fields E1, E2 and E3. Thus, the fact of not having to align the respective openings 12 of the input 8 and output 9 electrodes constitutes an advantage of the invention. The volume delimited by the bars 14 of a window 13 and the input 8 and output 9 electrodes constitutes an amplification space 22. The amplification stage A consists of one or more amplification spaces 22 depending on whether the spacer 11 has one or more windows 13. In a plane perpendicular to the electric field E2, the dimensions of the windows 13 are greater than the dimensions of the openings 12 of the input 8 and output 9 electrodes, which lead to the amplification spaces 22. For example, the width 1 of these bars 14, between two windows 13, in the plane of the plate constituting the spacer, is less than 100 microns and the bars are separated one from the other others with a pitch P less than 5 cm.

où

• y
  
  est la flèche au centre de chaque espace d'amplification 22,
• E est le module d'Young du matériau constituant la grille d'entrée 8 ou de sortie 9,
• I est le moment quadratique d'une portion de la grille d'entrée 8 ou de sortie 9, correspondant aux dimensions de chaque espace d'amplification 22,
• N est la précontrainte en tension de la grille d'entrée 8 ou de sortie 9, et
• ρ est la charge linéique électrostatique de l'électrode d'entrée 8 ou de sortie 9,

   ρ étant donnée par : $${\text{ρ = [ε}}_{\text{0}}{\text{ε}}_{\text{r}}\frac{{\mathit{\text{<figure-callout id="2" label="U" filenames="imgf0004.png,imgf0007.png" state="{{state}}">U</figure-callout>}}}^{\text{2}}}{\text{2}{\mathit{\text{e}}}^{\text{2}}}\text{].}\frac{\mathit{\text{S}}}{\text{2}\mathit{\text{l}}}\text{,}$$

où

• U est la tension appliquée entre les grilles d'entrée 8 et de sortie 9,
• ε₀ et ε_r sont respectivement les permittivités du vide et relative du milieu,
• e est l'épaisseur de l'entretoise, et
• S est la surface de la grille d'entrée 8 ou de sortie 9 couvrant chaque espace d'amplification 22.

The distance between two bars is determined as a function of the deflection of the input 8 and output 9 electrodes, under the effect of the electric field generated by the potential difference U to which they are subjected. It is estimated that the local deflection y suffered by the input 8 and output 9 electrodes is tolerable if it does not cause a gain variation of the amplifying structure 7 greater than 10% (this tolerance depends on the applications envisaged for the detector 1). If we consider that this arrow y, in the center of the distance D separating two bars must not be greater than 20%, so that the gain variations of the amplifying structure 7 are tolerable, the distance D must satisfy the inequality:

or

• there
  
  is the arrow in the center of each amplification space 22,
• E is the Young's modulus of the material constituting the inlet 8 or outlet 9 gate,
• I is the quadratic moment of a portion of the inlet 8 or outlet 9 gate, corresponding to the dimensions of each amplification space 22,
• N is the prestress in tension of the inlet gate 8 or outlet gate 9, and
• ρ is the electrostatic linear charge of the input 8 or output 9 electrode,

ρ being given by: $${\text{ρ = [ε}}_{\text{0}}{\text{ε}}_{\text{r}}\frac{{\mathit{\text{<figure-callout id="2" label="U" filenames="imgf0004.png,imgf0007.png" state="{{state}}">U</figure-callout>}}}^{\text{2}}}{\text{2}{\mathit{\text{e}}}^{\text{2}}}\text{].}\frac{\mathit{\text{S}}}{\text{2}\mathit{\text{l}}}\text{,}$$

or

• U is the voltage applied between the input 8 and output 9 grids,
• ε ₀ and ε _r are respectively the permittivities of the vacuum and relative of the medium,
• e is the thickness of the spacer, and
• S is the surface of the inlet 8 or outlet 9 gate covering each amplification space 22.

par la relation ci-dessus donne une valeur majorée de cette flèche. Autrement dit, il est possible de concevoir un détecteur 1 performant même si la distance D est égale, voire supérieure, à celle donnée par l'inégalité ci-dessus.It can be noted that the determination of the deflection there

by the above relation gives an increased value of this arrow. In other words, it is possible to design an efficient detector 1 even if the distance D is equal to, or even greater than, that given by the above inequality.

The optical opacity of such a spacer 11 is advantageously less than 30% and preferably less than 1%.

As shown in Figure 3, the anode 6 has a planar multilayer structure. It comprises an outer layer 15 and two inner layers 16, and a ground plane 17, the whole resting on an insulating substrate 28.

As shown in FIG. 4, the outer layer 16 is segmented into elementary or block anodes 15 forming a two-dimensional checkerboard network whose rows are aligned along axes of coordinates X and Y. Each block 15 forms a square of less than one millimeter aside, for example 650 microns. The blocks 15 are alternately assigned to the reading of one or the other of the coordinates X and Y. Two neighboring blocks 15 do not measure the position according to the same coordinate. The space between the blocks 15 is as small as possible, but must make it possible to maintain perfect insulation between them. Advantageously, this space is less than 100 microns.

As shown in FIG. 5, the internal layers 16 are formed of crossed conductive tracks 18. On one of the internal layers 16, the tracks 18 extend parallel to the first rows of blocks 15. On the other of the internal layers 16, the tracks 18 extend parallel to second rows of blocks 15, perpendicular to the first. In this example, the blocks 15 of a row associated with the X coordinate are located on an internal layer different from that connected to the blocks arranged in a row corresponding to the Y coordinate. The tracks 18 are separated from the blocks 15 by an insulator through which are drilled connection holes 19 (known to those skilled in the art under the Anglo-Saxon expression "via hole" ), lined with an electrically conductive material to ensure the electrical connection of the blocks 15 with the tracks 18 of one or the other of the internal layers 16 (see FIG. 3). The connecting holes 19 have for example a diameter of 100 microns.

The tracks 18 are separated from each other by the smallest possible distance while maintaining perfect insulation between them. The fact of having the tracks in superimposed layers isolated from each other makes it possible to gain integration while retaining the required quality of insulation.

The blocks 15, thanks to the tracks 18, are connected to fast amplifiers 20 themselves connected, via electronic reading channels, to electronic processing means 21 (see FIG. 5).

To limit the number of electronic reading channels, and consequently the cost of the detector 1, several blocks 15 belonging to the same row are connected to the same track 18. The number of blocks 15 separating two blocks connected to each other depends on their size and the technology used to make them.

By way of example, as shown in FIG. 6, each track 18 connects periodically, in a row, a block 15 out of four. As two neighboring blocks are connected respectively to tracks 18 extending along the axes X and Y, a track X1 connects two blocks spaced by three blocks, these three blocks comprising two blocks adjacent to the two blocks linked to track X1, themselves same connected respectively to tracks Y1 and Y7, separated by a block connected to a track X2, this arrangement being reproduced on the whole of the checkerboard made up of the blocks 15 (in FIG. 6, two blocks 15 connected together are represented by identical patterns).

When an ionizing particle I is emitted by the sample S, and it enters the detector 1 by the face 2a of the latter situated opposite to that close to the anode 6, it crosses the space of conversion C in which it interacts with the gas and generates primary electrons. These primary electrons, under the effect of the electric field E1, gain the amplification stage A, in which they are multiplied by avalanche, to form a cloud of electrons 23 (see Figure 1).

Part of this electron cloud 23 then crosses the output electrode 9 and enters the spreading space E. The electric field E3 prevailing in the spreading space E is moderate (<10 kV / cm) and conducive to a lateral spreading of the electron cloud 23 by diffusion of the electrons which constitute it, on the atoms and molecules of the gas. The thickness of the spreading space, in the direction of the electric field E3, as well as the nature of the gas and the size of the blocks are determined so that the spatial extension of the electron cloud 23, at the level from anode 6, covers several blocks 15 (at least two in each direction of the X and Y coordinates) and so that it is possible to thus determine the barycenter of the electron cloud 23. Isobutane stabilizes the avalanche process and to obtain a diffusion in the spreading space E, such that the avalanche extends over a sufficient number of blocks 15 to allow this determination of the barycenter of the electron cloud 23.

A current is then induced on a small group of blocks 15, and transmitted, via several electronic channels, to the electronic reading means 21. Thus, the position of each avalanche is determined in each X or Y coordinate. After rough determination of the avalanche position by identification of the lines 18 associated with the X and Y coordinates concerned, the load distributions measured on each block 15 are used to recalculate the position of the emitting point 24 of the original ionizing radiation. A precise measurement of this position can be obtained after correction of the geometric distortions due to the weighting method used to determine the barycenter of the electron cloud 23 interacting with the blocks 15 on which the measurement is carried out.

A second embodiment of the detector 1 according to the invention is shown in FIG. 7. It differs from the first embodiment described above essentially by the fact that the conversion space C and the amplification stage A are confused there. In this case, the detector 1 comprises a cathode 5 merged with the input electrode 8 and the sample S is placed directly in the vicinity of the input electrode 8 of the amplifying structure 7. The input electrode 8 acts as a cathode.

The polarization means 10 make it possible to create electric fields E2 and E3 respectively in the amplification stage A and in the spreading space E. The polarization means 10 drive the electrons from the input electrode 8, towards the anode 6.

In this embodiment, the amplifying structure 7 has a thickness, parallel to the electric field E2, of less than 300 microns. The spacer 11, defining the thickness of the amplification stage A, is adapted to the shape of the sample S.

Sample S emits an ionizing particle I. This interacts with the gas mixture to generate electrons of primary ionization. For the specific case of the detection of beta particles, a compromise is to be found between, on the one hand, a gas mixture sufficiently heavy for the beta particles to interact and, on the other hand, a gas mixture sufficiently light for the gain amplification is large enough to allow reading on an anode such as that described in connection with the first embodiment. Measurements have shown that this compromise can be achieved by using a mixture of gases at atmospheric pressure comprising neon and a few percent of isobutane.

A high electric field E2, greater than 25 kV / cm, is applied in the amplifying structure 7, which makes it possible to multiply the electrons of primary ionization. With an amplifying structure 7 such as that described in relation to the first embodiment, it is possible to obtain gains greater than 100,000, in proportional regime.

As for the first embodiment described above, the electrons multiplied in the amplifying structure are entrained by the field E3 of the spreading space before creating a current in the blocks 15 of the anode 6.

In such a detector 1, it is the electrons created near the cathode, that is to say near the sample S, which are preferentially multiplied and the parallax effects originating from the isotropic emission of the emitting sources. of the sample S are greatly reduced. Such a detector 1 also makes it possible to overcome the effects of the trajectory of the particles incident in the gas, including for high energy particles such as those conventionally emitted by markers. isotopes used in biology. This detector 1 thus makes it possible to very precisely locate the position of the emitting points 24 of ionizing radiation, whatever the isotopic markers used. The detector 1 makes it possible to obtain distribution curves indicative of the position of the source points, having a width at half height less than 100 microns.

A third embodiment of the detector 1 according to the invention is shown in FIG. 8. It differs from the second embodiment described above essentially by the fact that the input electrode is replaced by a face of the sample S, possibly metallized to make it conductive or polarized from the rear when it is partially conductive. In this case, the detector 1 does not have an independent cathode 5 and it is the sample S which acts as a cathode.

A fourth embodiment of the detector 1 according to the invention is shown in FIG. 9. It differs from the second embodiment described above essentially by the fact that it comprises several amplifying structures 7a, 7b and 7c, similar to the amplifying structure 7 already described in relation to the second embodiment, but superimposed so that the input electrode 8 of the amplifying structure 7b is merged with the output electrode 9 of the amplifying structure 7a which itself is superimposed, and so on for the underlying amplifying structure.

According to the embodiment shown in FIG. 9, the detector 1 also includes another amplifying structure 7d, located between the stack of amplifying structures 7a, 7b and 7c and the anode 6.

The amplifying structures 7a, 7b, 7c and 7d of this embodiment can be identical to each other or be of different geometries.

Many combinations of the stacks described above can be designed, within the framework of the invention, according to the envisaged application. The choice of introducing one or more different amplifying structures into the detector 1 depends on the application for which the detector 1 is intended. Thus, to allow isotopic separation of the markers in autoradiography, to limit the phenomena of discharges during detection of high energy particles, or obtaining higher gains with incident radiation such as X-rays, the use of several superimposing amplifying structures is particularly advantageous.

A fifth embodiment of the detector 1 according to the invention is shown in Figure 10. It differs from the embodiments already described above essentially by the fact that the anode 6 as described above is replaced by a conductive grid 25 of high transparency (advantageously greater than 80%). This grid 25 consists for example of a flat plate pierced with holes or a woven grid. In this embodiment, the amplifying structure is associated with an optical reading of the scintillation light emitted during the amplification process, by interaction of the electrons with the gas mixture contained in the detector 1. For this, it is necessary to use a particular quencher, such as, for example, triethylamine, which emits around a wavelength equal to 280 nanometers. This wavelength is compatible with the transparency of the optics (quartz or fluorine, for example) and the spectral sensitivity of the usual photo-cathodes of image intensifiers generally used for reading by CCD camera.

Advantageously, the autoradiographic imaging device 29 comprises a sample holder 30 adapted so that the detector 1 is placed within 50 microns of the sample S emitting ionizing radiation, mounted on this sample holder. In this case, the input electrode is advantageously constituted by an at least partially electrically conductive face (possibly metallized) of the sample S placed on the sample holder 30.

The grid 25 makes it possible to apply a potential while letting the scintillation light pass. This scintillation light is collected by a CCD camera 26 coupled to a light intensifier, through an exit window 27. This exit window is transparent to the wavelengths emitted and closes the detector 1.

The calculation of the barycenter of the light spot created by each avalanche makes it possible to determine, as for the detection by paving stones described above, the position of the emitting point 24 of the initial ionizing particle I.

FIG. 11 schematically represents a device 29 for autoradiographic imaging comprising a detector 1 according to the fifth embodiment described above. According to a variant, the detector 1 of this imaging device is replaced by a detector 1 such as those described in relation to the first, second, third and fourth embodiments.

Claims (14)

Radiation detector comprising: - an enclosure (2) containing a medium suitable for generating electrons under the effect of radiation, a conversion space (C) in which the radiations generate electrons, this conversion space (C) comprising a cathode (5) through which the radiations to be detected penetrate, - an anode (6) for generating signals as a function of a current generated by the displacement of charges in the vicinity of this anode (6), these charges corresponding to electrons and ions whose radiation is directly or indirectly to the origin, - polarization means (10) generating an electric field adapted to drive electrons in the direction going from the cathode (5) towards the anode (6), - at least one amplifier structure (7), located between the cathode (5) and the anode (6), each amplifier structure (7) comprising an input electrode (8) and an output electrode (9), maintained separated by an insulating spacer (11) comprising at least one electron amplification space (22) in which electrons are generated by avalanche from electrons generated by radiation, each amplification space (22) having lateral dimensions (D), in a plane perpendicular to the electric field, greater than the distance (e) separating the input (8) and output (9) electrodes, and each amplification space opening onto at least one opening (12) the output electrode (9), to allow at least part of the electrons generated by an avalanche to pass, characterized by the fact that the lateral dimensions (D) of dimensions (α), in a plane perpendicular to the electric field, of each opening (12) of the output electrode (9) on which this amplification space (22) opens. Detector according to claim 1, in which the input electrode (8), the output electrode (9) and the spacer (11) are respectively made up of independent elements and adapted to be separated. Detector according to one of the preceding claims, in which the spacer (11) consists of a plate of insulating material substantially perpendicular locally to the electric field, drilled right through in the direction parallel to the electric field, at least a window (13) open both on the input electrode (8) and on the output electrode (9), each window (13) delimiting an amplification space (22), having a dimension D perpendicularly to the electric field satisfying:

or - y

is the arrow in the center of each amplification space (22), - E is the Young's modulus of the material constituting the inlet (8) or outlet (9) grid, I is the quadratic moment of a portion of the inlet (8) or outlet (9) grid, corresponding to the dimensions of each amplification space (22), - N is the prestress in tension of the inlet (8) or outlet (9) grid, and - ρ is the electrostatic linear charge of the input (8) or output (9) electrode, ρ being given by: $${\text{ρ = [ε}}_{\text{0}}{\text{ε}}_{\text{r}}\frac{{\mathit{\text{U}}}^{\text{2}}}{\text{2}{\mathit{\text{e}}}^{\text{2}}}\text{].}\frac{\mathit{\text{S}}}{\text{2}\mathit{\text{l}}}\text{,}$$

or - U is the voltage applied between the input (8) and output (9) grids, - ε _o and ε _r are respectively the permittivities of the vacuum and relative of the medium, - e is the thickness of the spacer (11), and - S is the surface of the inlet (8) or outlet (9) grid covering each amplification space (22). Detector according to claim 3, in which the spacer (11) comprises at least two windows (13) separated from each other by a bar (14) whose thickness (1) between these two windows (13) is lower
or equal to the dimension (e) of this bar parallel to the electric field, which is itself less than or equal to 500 microns. Detector according to one of the preceding claims, comprising an amplifying structure for which the amplification space (22) coincides with the conversion space (C), the input electrode of this amplifying structure (7) corresponding at the cathode (5). Detector according to claim 5, in which the input electrode (8) is formed from an at least partially conductive face of a sample (S) emitting radiation. Detector according to one of the preceding claims, comprising several amplifying structures (7) stacked, between the cathode (5) and the anode (6), in the direction of the electric field. Detector according to claim 7, in which the output electrode (9) of a first amplifying structure (7) is merged with the input electrode (8) of a second amplifying structure arranged between the first amplifying structure ( 7) and the anode (6). Detector according to either of Claims 7 and 8, in which at least two amplifying structures (7) have different geometries. Detector according to one of the preceding claims, comprising a spreading space (E) located between the anode (6) and the output electrode (9) facing the anode (6), and in which there is a electric field (E3) suitable for spreading, in directions perpendicular to this field (E3), electrons by diffusion on the atoms and molecules of the medium contained in the enclosure (2). Autoradiographic imaging device comprising a detector (1) according to one of the preceding claims and a sample holder (30) adapted so that the detector (1) is placed within 50 microns of a sample (S) emitting radiation, mounted on the sample holder (30). Device according to claim 11, in which the input electrode (8) consists of an at least partially conductive sample (S) disposed on the sample holder (30). Device according to either of Claims 11 and 12, in which the anode (6) is transparent to the optical signals, this device further comprising a device for optical reading of these signals. Device according to either of Claims 11 and 12, in which the anode (6) comprises a plurality of elementary anodes (15) connected to at least one reading channel by tracks, each reading channel being connected to several elementary anodes (6).

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