WO1998014981A1

WO1998014981A1 - Sensor with ionising radiation gas with high counting rate for a radioactive tracer

Info

Publication number: WO1998014981A1
Application number: PCT/FR1997/001736
Authority: WO
Inventors: Georges Charpak
Original assignee: Georges Charpak
Priority date: 1996-10-02
Filing date: 1997-10-01
Publication date: 1998-04-09
Also published as: EP0929908A1; FR2754068B1; FR2754068A1

Abstract

The invention concerns a sensor with ionising radiation gas comprising combined in a pressurised gas chamber a module (1) for absorbing ionising radiation, generating electrons, and a module (2) for amplifying these electrons by electronic avalanche process. A module (3) for sensing and reading electronic avalanches comprises a sensing electrode (31) provided with a plurality of elemental sensing electrodes (31i) and an interface circuit (30, 32) coupled with the sensing electrode (31) provided with a plurality of sensing outputs and ensuring the tightness of the gas chamber. The invention is applicable to nuclear medicine and crystallography.

Description

Ionizing radiation gas detector with very high counting rate

The invention relates to a gas detector for ionizing radiation, such as X-rays, with a very high counting rate, usable in particular in medical imaging and / or in crystallography.

X-ray imaging covers broad areas of application, including nuclear medicine and crystallography.

At present, there are many types of gas detectors, based for example on the implementation of wire chambers, these detectors being used in the abovementioned fields. As an illustrative example of such detectors, mention may be made in particular of the spherical drift chamber used for studying the structure of macromolecules by X-ray diffraction, the X-ray used having an energy of the order of 10 keV. For a more detailed description of this type of detector, one can usefully refer to the article entitled "Α fast X-Ray d ± ffractometer based on a εpherical dr ± ft mul t ± w ± re proport ± onal chamber '' published by R.KAHN, R. FOURME, B.CAUDRON, R.BOSSHARD, LURE (CNRS-UPS), 91405 Campus d'Orsay, France and Laboratoire de Physico-chimie Structurale, Université Paris XII, 94010 Créteil, France; R. BENOIT, R. BOUCLIER, G. CHARPAK, JC SAN- TIARD and F. SAULI, CERN Geneva, Switzerland, and edited by Nuclear Instruments and Methods 172 (1980) 337-344, North-Holland Publishing Company, and in the article entitled "Some Propert ± es of Spher ± cal Dr ± ft Chambers" published by G.CHARPAK, C.DEMIER- RE, R.KAHN, JC SANTIARD and F.SAULI, CERN Geneva, Switzerland, and edited by Nuclear Instruments and Methods 141 (1977) 449-455, North-Holland Publishing Company.

In addition, a type of xenon pressure chamber of 3 bars has also been used for γ radiation imaging of energy of the order of 60 keV in medicine. nuclear. Such a type of room, described in the article entitled "Cl ± n ± cal Αppl ± cat ± ons of a Pressur ± zed Xenon Wire Charnier Gamma Camera Ut ± l ± z ± ng the Short L ± ved Agent Ta", published by JL LACY, MS VERANI, ME BALL and R. ROBERTS, Baylor College of Medicine, Houston, Texas 77030, USA and edited by Nuclear Instruments and Methods in Physics Research A 269 (1988), 369-376 North-Holland, Amsterdam, at best, achieves a count rate of 850,000 cps (counts per second) and a spatial resolution of 2.5 mm.

In the two above-mentioned examples, the maximum counting rate tolerated by the wire chambers which make it possible to locate the X-rays is essentially limited by two factors: - the first factor is inherent in the very structure of the wire chambers, which do not tolerate effective count rate greater than about 10 ⁴ c / s.mm ² ;

- the second factor is inherent in the electronics used to read the position of avalanche phenomena generated by ionizing radiation.

The object of the present invention is to remedy the abovementioned drawbacks and limiting factors of the detector devices of the prior art, by using an ionizing radiation detector making it possible to gain up to a factor of one thousand in the counting rate obtained. . Another object of the present invention is the implementation of an ionizing radiation detector having specific construction characteristics making it possible to exploit the aforementioned counting rates in a simple and economical manner.

The ionizing radiation gas detector, object of the present invention, is remarkable in that it comprises, in combination, a pressurized gas enclosure, a module for absorbing this ionizing radiation making it possible to generate electrons from of this ionizing radiation, an amplification module by downstream phenomenon che electronic of these electrons, a circuit for detecting and reading these electronic avalanches comprising at least one detection electrode having a plurality of elementary detection electrodes intended to detect the electric charge of said avalanches, an interfacing circuit electrically coupled to the detection electrode, this interfacing circuit comprising a plurality of detection outputs and making it possible to seal the gas enclosure. The gas detector of ionizing radiation, object of the present invention, finds application in nuclear medicine and crystallography, in particular.

It will be better understood on reading the description and on observing the drawings in which: - Figure 1 shows an illustrative gas detector of ionizing radiation, according to the object of the present invention;

- Figures 2a and 2b show an illustrative gas detector of ionizing radiation in the case of the implementation of an asymmetric type wire chamber, respectively an improved asymmetric chamber for obtaining counting rates very high ;

- Figure 3a shows, in a perspective view, a detail of the detector, object of the invention, as shown in Figures 1 or 2a, 2b;

- Figure 3b shows a front view of the detail of embodiment shown in Figure 3a;

- Figure 4a shows, in a perspective view, a detail of the detector object of the invention, as shown in Figures 1 or 2a, 2b, when the detection electrode and the detection counter-electrode are formed by a multilayer assembly;

- Figure 4b shows a front view of the detail of embodiment of Figure 4a;

- Figure 4c shows a sectional view, along the section plane P of FIG. 4a;

- Figures 5a to 5e show an alternative embodiment of the detector shown in Figures 4a to 4c, in an application more particularly intended for crystallography in the case of diffraction of LAUE.

A more detailed description of a gas detector for ionizing radiation, object of the present invention, will now be given in conjunction with FIG. 1 and the following figures. As shown schematically in FIG. 1 above, the ionizing radiation gas detector, object of the invention, comprises, in a pressurized gas enclosure, a module 1 for absorbing this radiation making it possible to generate electrons from the latter, and a module 2 for amplification by electron avalanche phenomenon of these electrons. In FIG. 1, the gas enclosure bears the reference E. Of the conventional type, it can be provided with either a lateral intake window allowing the admission of a beam of ionizing radiation in a sheet, this window being denoted Fel in FIG. 1, either of a so-called top window, denoted Fes, allowing the admission of ionizing radiation from an object to be studied such as an isotopically marked laboratory section or, if applicable if necessary, in the case of crystallography, from radiation diffracted by crystals or by any crystalline or amorphous body to be studied under X-ray type radiation for example.

In addition, the detector, object of the present invention, comprises a circuit 3 for detecting and reading the electronic avalanches generated in the amplification module 2, this detection and reading module 3 comprising at least, as shown in the FIG. 1 above, a detection electrode, denoted 31, preferably having a plurality of elementary detection electrodes intended to detect the electric charge of the above-mentioned electronic avalanches and an interface circuit. cage 31 electrically coupled to the detection electrode 30. The interfacing circuit 31 preferably comprises, as will be described later in the description, a plurality of detection outputs and of course allows sealing gas from the gas enclosure E previously described.

With regard to the embodiment of the module 1 for absorbing ionizing radiation and the module 2 amplification by avalanche phenomenon of the electrons created as a result of this ionization, it is indicated that this embodiment generally corresponds to the use of chambers with asymmetric type wires, respectively of improved asymmetric type, the latter type of chamber making it possible in particular to achieve very high counting rates, greater than 10 ⁷ c / s.mm ² .

In general, it will be recalled that with regard to the use of chambers with asymmetric type wires, the module 1 for absorbing ionizing radiation and the module 2 for amplification by electronic avalanche phenomenon correspond to those described in the publication entitled "AH ± gh-Rate. H ± gh-Resolut ± on Asymmetr ± c Vl ± re Chamber w ± th M ± crostr ± p Readout" published by G.CHARPAK, I.CROTTY, Y. GIOMATARIS , L.ROPELEWSKI and MCS WILLIAMS, CERN, Geneva, Switzerland, published by the Nuclear Instruments and Methods in Physics Research, under the reference NIM A 376, 1996, page 29. In the case of the implementation of a wires of asymmetric type as described above and represented in FIG. 2a, it is further recalled that the detection electrode 31 forms a cathode electrode, while the elementary detection electrodes constituting this detection electrode themselves form electrodes of elementary cathode. For a more detailed description of the implementation of asymmetric type wire chambers and, in particular, of a specific embodiment thanks to the use of electrical potentials for polarization of the grid G delimiting the absorption module 1 and the amplification module 2, as well as on the relative distance values Dl, D2 separating these electrodes, the amplification module 2 being constituted by a succession of anodes and cathodes constituting in fact the wire chamber, reference may also be made to American Patent No. 5,521,956 issued in the name of Georges CHARPAK, the text of this document being introduced in the present description for reference.

With regard also to the use of chambers of the improved asymmetric chamber type, however, it is indicated that the module 1 for absorbing ionizing radiation and the module 2 for amplification by avalanche phenomenon are formed, as described in relation to FIG. 2b, by a first G, a second G 'and a third parallel flat electrode, denoted 31, the third electrode 31 being distant from the second electrode G' by a distance D2 of less than 200 μm and constituting a anode electrode, this electrode of course forming the detection electrode 31, which is constituted by elementary anodes, as will be described later in the description.

For a more detailed description of the conditions for implementing an improved or optimized asymmetric chamber and, in particular, the polarization conditions of the aforementioned different electrodes, reference may also usefully be made to French patent application No. 96 06600 filed by Georges CHARPAK, this patent application being introduced in the present description by way of reference. In the case of the use of asymmetric type wire chambers, as shown in FIG. 2a, it is recalled in particular that the choice of dimension D2, distance between the electrode formed by the anode and cathode A wires , K successive and the detection electrode 31, of the order of 500 μm, for a distance Dl = 3 mm, separating the grid G from the same succession of anode and cathode wires A, K, saves a factor of 10 on the counting rate of conventional rooms with symmetrical structure.

On the contrary, in the case of the use of an improved or optimized asymmetric chamber, as shown in FIG. 2b, the increase in counting rate is even greater due to the structure and dimensioning parameters, in particular the grid G ', values of electric field in the space separating the grid G and the grid G', field El, and of the space separating the grid G 'of the detection electrode 31, the distance D2 separating the electrode G ′ of this detection electrode 31 being less than or equal to 200 μm. These parameters allow counting rates greater than or equal to 10 ⁷ c / s .mm ^{2 to be} obtained. In both cases, whatever the implementation of the improved or optimized asymmetrical or asymmetrical wire chamber type, in accordance with FIGS. 2a or 2b, the gas detector, object of the present invention, allows, for each of the modes of implementation, the choice of a detection and reading circuit adapted to the aforementioned counting parameters and ultimately, to the resolution of each type of asymmetric chamber, respectively asymmetric improved or optimized, used, that is to say finally to the dimension or diameter of the electronic avalanches obtained thanks to the implementation of the aforementioned chambers.

It is understood in particular that the detection circuit implemented in accordance with the object of the present invention allows, in a gas enclosure containing a mixture of xenon under pressure of the order of 6 bars plus a gas such as methane by example, preventing secondary discharges by a mechanism known from the prior art, saving as much as possible the number of sealed electrical connections between the inside and the outside of the gas enclosure, that is to say say at the level of the interface circuit proper. It is indeed indicated that the reckless multiplication of the number of these electrical connections is expensive, in particular in production and in risk of gas leakage at such high pressures, when it is necessary to be able to ensure a high counting rate and a two-dimensional location, for example over the entire surface of the detector.

For this reason, the interfacing circuit 3 implemented in the gas detector, object of the present invention, has two complementary embodiments, more particularly suitable for use, that is to say an asymmetrical type chamber of wires. , either of an improved or optimized asymmetric type chamber.

In a first embodiment more particularly intended for the use of an asymmetrical type wire chamber for example, it is indicated, as shown in particular in FIG. 3a, that the interfacing circuit 3 can advantageously comprise a counter-electrode detection, bearing the reference 32, this detection counter electrode having a plurality of elementary detection counter electrodes 32i, as shown in FIG. 3a above.

Each elementary detection counter-electrode is electrostatically coupled to at least one elementary detection electrode, in order to allow the transmission of the detected electric charge of the electronic avalanches with a view to their counting. Of course, the detection electrode and detection counter electrode 31, 32 and the elementary detection electrodes and elementary detection counter electrodes 31i, 32i, make it possible to ensure gas tightness of the gas enclosure E under pressure. In a particular embodiment, it is indicated that the detection electrode 31 and the detection counter electrode 32, formed respectively by the elementary detection electrodes 31i and by the elementary detection counter electrodes 32i, are advantageously formed by at minus a layer of electrical insulating material, marked 30. This layer of electrically insulating material insulator can be formed by a blade with substantially parallel faces made of a dielectric material such as CAPTON. The blade of dielectric material 30, when it is made of CAPTON, can have a thickness of the order of 50 μm. As shown in FIG. 3a above, a first face FI of the blade 30 is placed inside the gas enclosure E and is provided with electrically conductive elements each forming an elementary detection electrode 31i, as shown in Figure 3a. The second face F2 of the blade 30 is placed outside the gas enclosure E and is provided with electrically conductive elements each forming an elementary detection counter-electrode bearing the reference 32i.

As shown in the above-mentioned figure, the elementary detection electrodes 31i and the elementary detection counter-electrodes 32i are aligned in two oblique directions, preferably orthogonal, so as to allow two-dimensional tracking X, Y of the electronic avalanches. Of course, it is understood that the elementary detection electrodes 31i and the elementary counter-electrodes 32i are of identical shape and size and are placed opposite so as to ensure optimum electrostatic coupling between electrode and counter respective elementary electrode. The two alignment directions are preferably orthogonal to ensure the two-dimensional location X, Y along lines X _: to X _n and columns Y- to Y _n as shown in the aforementioned figure.

Preferably, as shown in particular in FIG. 3a, the elementary detection electrodes 31i and the elementary detection counter-electrodes 32i are advantageously constituted by zones of electrically conductive material of substantially square shape and aligned to form a checkerboard. This checkerboard constitutes a two-dimensional detection matrix.

Regarding the detection electrodes elementary 31i, it is indicated that, advantageously, these can be covered with a thin layer of semiconductor material 301 such as germanium for example, by spraying, this thin layer of semiconductor material 301 being brought to a fixed potential such as the reference potential or the ground potential of the detector. The layer of semiconductor material 301 thus makes it possible to connect each elementary electrode 31i to the reference potential by means of a high value resistor, of several egohms, which thus makes it possible to fix the direct potential of each elementary electrode 31i to ensure stable operation of the detector. It is thus understood that during the appearance of an electronic avalanche, the time constant produced by the circuit constituted by an elementary detection electrode 31i and the resistance of the layer of semiconductor material 301 connected to the fixed potential makes it possible to place the elementary electrode considered, as well as, if appropriate, the neighboring elementary electrodes, at the electric potential generated by the charges of the electrons of the avalanche, this electric potential being immediately transmitted by electrostatic coupling to the elementary counter-electrodes of detection 32i in vis- with respect to the aforementioned elementary detection electrodes. As regards the elementary detection counter-electrodes 32i, it is understood that these are connected alternately to counting lines with n conductors, one conductor per line or column of elementary electrodes / counter-electrodes, these counting lines being referenced X _: to X _n for the direction of two-dimensional detection in FIG. 3a, and Y- to Y _n for the direction of two-dimensional detection Y. Of course, it is necessary that the parameters of the chamber make it possible to influence electrically two elementary detection electrodes. Each counting line is electrically connected to a zone conductive forming an elementary detection counter-electrode on the basis of one electrically conductive zone on two of each row or column of elementary electrodes / counter-electrodes for a conductor constituting a counting line. It is in fact understood that as regards the elementary detection electrodes 31i, it is not necessary to connect the latter to counting lines, which thus avoids the creation of electrical connection in leaktight passage, the electrical connection to each elementary detection counter-electrode 32i being sufficient and thus making it possible to ensure counting and two-dimensional detection of avalanche phenomena generated by ionizing radiation.

Of course, it is understood that each conductor of a given row counting line i can then be associated at the output with a vernier type device, bearing in FIG. 3a the references 33X, respectively 33Y for the lines X- to X _n , respectively columns Y- to Y _n , this vernier-type device making it possible to detect the rank of the conductor constituting the counting line and, ultimately, the address i of the detection counter-electrode 32i in the line and the corresponding column. Such vernier-type devices will not be described in more detail because they correspond to elements of the state of the art described in French patent application No. 2,680,010 in the name of Mr. Georges CHARPAK.

A preferred embodiment of the interfacing circuit 3 described above in conjunction with FIG. 3a will now be given in conjunction with FIG. 3b. According to the above-mentioned figure, it is indicated that each conductive area constituting an elementary detection electrode 31i, respectively of an elementary detection counter-electrode 32i, is of substantially square shape and each subdivided into two triangular elements 31il, 31i2; 32il, 32i2 separated by a diagonal space. One triangular element on two successive triangular elements then forms an elementary detection counter-electrode in the direction of travel of one X or the other Y two-dimensional detection direction, each corresponding triangular element being interconnected with a counting line, that is to say with a same conductor forming the aforementioned counting line, assigned to two-dimensional directions.

In FIG. 3b, it can be observed that, for example, each upper left triangular element is connected to a conductor forming a counting line associated with the vertical direction, that is to say to a column, while each triangular element lower right is on the contrary connected to a conductor of a horizontal counting line, that is to say to the counting line associated with a line in the direction X.

In addition, as shown in FIG. 3b above, it is indicated that each conductive zone can have a dimension or side of value c and be spaced from any adjacent conductive zone in the direction X respectively Y by a distance p to constitute the checkerboard or two-dimensional detection matrix. It is understood of course that the parameters c and p can advantageously be chosen as a function of the value D of the average diameter of the avalanches generated in the detector. Thus, for an avalanche diameter of the order of 2 mm, this value corresponding for example to the implementation of an asymmetric wire chamber, the distance p separating two successive elementary detection electrodes, respectively two counter-electrodes of successive elementary detection, can be taken equal to 100 μm, and the value of dimension c or side of each conductive zone can be taken equal to 1 mm.

When, of course, several adjacent triangles are affected, that is to say subject to the phenomenon of electrical influence by the avalanche phenomenon, the detection by means of the vernier devices previously mentioned, in X and Y, that is to say by determining the rank of the conductor constituting the corresponding counting line, makes it possible to determine the address of the triangle subjected to the strongest electrical influence and therefore to determine the position of the corresponding avalanche center. Of course, electronic processing of the signals thus obtained can be carried out using a processing of the barycenter type for example.

Finally, and with the aim of supporting the pressure difference between the interior medium of the chamber of the gas enclosure E and the exterior, it is understood that on the face F2 of the blade 30 of CAPTON as represented in FIG. 3a for example, it is possible to apply to the exterior a retaining layer made of an electrically insulating material but sufficiently resistant to allow the flatness of the assembly to be maintained. This holding system will not be described in detail since it corresponds to a system known from the state of the art. Finally, since the conductors X ₁ to X _n , Y _x to Y _n constituting the counting lines are not placed in the plane of the face F2, their wiring can be organized in the most appropriate manner.

When, for the implementation of a detector in accordance with the object of the present invention, an improved or optimized asymmetric chamber is used, the dimension D of the avalanches obtained at the level of the detection electrode is much smaller. It is recalled in fact that for a distance D2 as represented in FIG. 2b equal to 200 μm for example, distance separating the grid G from the detection electrode 31, the dimension D has the value substantially 200 μm also. Under such conditions, the interfacing circuit 3 described previously in the description appears less well suited to the detection of avalanche phenomena of such dimensions.

In such a case, on the contrary, it appears preferable to implement a specific interfacing circuit 3, based on a similar principle but presenting certainly born peculiarities. Such an interfacing circuit can then be obtained from the substantially square conductive areas forming the elementary detection electrodes, as described for example in FIGS. 3a or 3b, and by conferring on these elementary detection electrodes 31i a plane configuration in the two-dimensional detection plane X, Y adapted to the corresponding plane dimension of the avalanches.

This adaptation makes it possible to optimize the spatial resolution of the elementary detection electrodes 31i placed on the face FI of the interfacing circuit considered. Of course, in such a case and in a particularly advantageous manner, the interfacing circuit 3 can be formed by a circuit of the multilayer printed circuit type formed by a set of superimposed elementary layers, as shown in FIG. 4a. By way of nonlimiting example, the interfacing circuit shown in the aforementioned figure only comprises, in order not to overload the drawing, a number of layers limited to three, Cl, C2, C3. Of course, a larger number of layers can be provided.

As will be observed in FIG. 4a above, one of the faces FI of the multilayer printed circuit is oriented towards the interior of the gas enclosure E and of course includes the detection electrode 31.

As will also be observed in FIG. 4c, according to a sectional view along the section plane P of FIG. 4a, each elementary layer comprises a plurality of interlayer electrical connections, making it possible to ensure the electrical connection of the electrodes of elementary detection towards another face of the multilayer printed circuit oriented towards the outside of the gas enclosure E. Of course, the electrical connections are impermeable to the gas contained in the gas enclosure. As regards the planar configuration of the elementary detection electrodes 31i, it is thus indicated as shown in FIG. 4b, and due to the small size of the abovementioned avalanches in the case of the use of an improved or optimized asymmetrical chamber, that the conductive zones can then advantageously be each formed by a plurality of concentric rings, noted 31il to 31i4 for example for the conductive area 31i of FIG. 4a. It will thus be understood that the subdivision of each conductive zone into concentric rings makes it possible to adapt each conductive zone considered, and finally each elementary detection electrode, to the resolution, much finer, necessary for the detection of avalanches whose dimension was previously indicated.

In FIG. 4b, in particular, the concentric rings 3111 to 31i4 have been shown, four rectangular concentric rings having been shown for the conductive area 31i in FIG. 4a.

According to a particularly advantageous aspect, it is indicated that, in such a case, each crown of even odd even rank, starting from the center for example, is interconnected in parallel in the direction Z perpendicular to the directions X, Y of two-dimensional detection, c ' that is to say the direction Z of the thickness of the multilayer circuit, the crowns of respectively odd even-numbered rank being assigned to one respectively to the other X, Y of the two-dimensional detection directions. Such an embodiment makes it possible to reduce the number of outputs while maintaining a high counting rate.

It is in fact understood, as shown in FIG. 4c, that a counter electrode 32i can be associated with each electrode 31i, the counter electrode 32i not being electrostatically coupled to the latter but, on the contrary, electrically connected by internal electrical connections in the thickness of the multilayer printed circuit formed by layers C1, C2, C3. It is thus possible, by the repetition of each detection electrode elementary 31i and its subdivisions into concentric crowns 31il to 31i4, as shown in FIGS. 4a, 4b and 4c, with their elementary detection counter-electrodes 32i, and where appropriate their subdivisions into concentric elementary crowns 32il to 32i4, as well as shown in FIG. 4c, to reconstruct an interfacing circuit similar to that described above in connection with FIGS. 3a and 3b with regard to the counting lines for example. However, the repetition of each elementary detection electrode 31i into an elementary detection counter-electrode 32i does not appear to be necessary, as will be described below in the description.

It is thus understood that the subdivision, on the one hand, of each elementary detection electrode into concentric rings for example and the association of a number of superimposed elementary layers constituting a multilayer interfacing circuit, this number of elementary layers being equal to the number of crowns -1 constituting each elementary detection electrode, makes it possible to carry out a much more elaborate counting, adapted to much smaller avalanche sizes.

In particular, taking into account the technology used for the implementation of the multilayer printed circuit, when the technique used makes it possible to produce sealed outputs every 2.5 mm only, each elementary electrode 31i can then be produced in the form of a printed circuit on the IF face of the multilayer circuit from strips with a width of 100 μm separated by intervals of 50 μm for example. The aforementioned strips are then electrically connected via the interlayer connections alternately to the corresponding conductors of the counting lines associated with the direction X, Y respectively of two-dimensional detection. For a room with a 25 cm x 25 cm square interface circuit, it is possible to obtain, as shown in FIG. 4c, in the absence of repetition of each elementary detection electrode 31i into an elementary detection counter-electrode 32i, one hundred sealed outputs spaced apart from the minimum value of 2.5 mm for example. The number of outputs thus appears reduced and compatible with the technology used thanks to the use of multiple layers while maintaining the resolving power thanks to the subdivision of the elementary detection electrodes, as represented in FIG. 4c.

The embodiment as shown in FIGS. 4a, 4b and 4c appears to be particularly well suited to the implementation of a detector according to the object of the present invention, using an improved or optimized asymmetric chamber in which the distance D2 is taken equal to 200 μm for example and that the dimension D of the avalanche is of the order of 200 μm also. By dimension D of the avalanche is actually meant the corresponding dimension of the area of influence of the avalanche. In such a case, and in the context of the aforementioned embodiment, there are always at least two crowns on which a signal is induced.

It then suffices to provide a reading system making it possible to calculate the electric barycenter of the pulses collected on the conductors of the counting lines in the directions X and Y previously mentioned to obtain an accuracy which is much better than the overall size of each detection electrode. elementary 31i.

Of course, this technique also makes it possible to implement analog reading methods such as by means of the vernier systems previously described in the description. Indeed, the abovementioned analog methods make it possible to carry out an interpolation, which makes it possible to obtain a precision much greater than the effective width of the row or of the column constituted by the set of concentric rings.

It is also possible to include in the intermediate rings constituting each elementary detection electrode 31i of the delay lines printed in order to obtain the corresponding positioning. This technique corresponds to a conventional technique and, as such, will not be described in detail.

The previously described interfacing circuit, implemented in a gas detector of ionizing radiation, object of the present invention, effectively makes it possible to reduce the number of sealed outputs necessary for counting with a high counting rate and a high resolution.

The embodiments described above appear particularly well suited for the implementation of high pressure xenon detectors which can be used, on the one hand, in wide collimated beam imaging applications used for nuclear medicine, application for which the precision sought is of the order of 2 mm and the counting rate is equal to 5 MHz, that is to say 5 × 10 ⁶ c / s and, on the other hand, for an application of imaging of beams generated by a substantially point radiation source applied to crystallography.

In this application, in the case of BRAGG diffraction, a phenomenon for which a large number of small spots is distributed over the surface of the detection electrode 31, elementary electrodes 31i as shown in FIGS. 4a, 4b and 4c can advantageously be used. Thus, the entire surface of the detection electrode 31 is covered by a matrix of elementary electrodes, as shown in FIG. 4a.

In the case where the diffraction phenomenon is that of the LAUE diffraction, the diffraction pattern corresponds to a single series of concentric circular spots. In the context of such a phenomenon, it is appropriate to detect the distribution of the diffracted intensity as a function of the radius, distance from the center of the pattern. The counting rates are then huge. In this case, the interfacing circuit shown in FIG. 5a comprises a network of concentric circular zones. It can be produced by means of a printed circuit comprising circular bands centered on a common point 0 and of width 100 μm, for an accuracy of the order of 100 μm. The multilayer structure, as shown in Figures 4a to 4c, can then be advantageously used, so as to have a strip output. It is thus possible to have 250 outputs for a network comprising 250 concentric bands. Such an embodiment is entirely realistic insofar as the printed circuit technology allows the creation of watertight crossings in steps of 1.2 mm, or 1500 watertight crossings over an area of approximately 4.6 x 4.6 cm. . In addition, each circular zone constituting the elementary detection electrodes 31i can, as shown in FIG. 5b, be subdivided into a plurality of identical segments, each segment corresponding to a determined counting capacity. This subdivision into segments will be used when the counting rates are very high, the segments being said to be identical when these segments have an identical surface. In Figure 5b, there is shown a subdivision into four sectors so as not to overload the drawing. However, and in the case where a circle or circular zone with a diameter of 5 cm is used to constitute an elementary detection electrode 31i for example, the set of circular zones can be subdivided into one hundred parts of 1.5 mm, each part or segment being connected to counting electronics whose counting capacity is of the order of 1 MHz for example. It is then possible to count with a counting speed of 100 MHz for the entire elementary detection electrode 31i, which of course makes it possible to envisage an application with a detector in accordance with the object of the present invention, in the embodiment thereof from an improved or optimized asymmetric chamber. In such a case, a gas detector in accordance with the object of the present invention achieves performance comparable to that of the erasable phosphor detectors normally used in these applications due to the very large radiation intensities emitted from X-ray sources. synchrotrons.

In addition, if the counting rate is enormous, for example greater than 10 ⁸ Hz, each circular band can for example be subdivided into 20 sectors of angle at the center of 18 °. Each sector can then, in a particularly advantageous manner, be constituted so as to form an elementary electrode 31i formed by a ring pattern, as shown previously in FIG. 4a. In this application, however, the crown patterns, as shown in FIG. 5c, retain the general shape of the circular sectors, with an opening angle of 18 °. In this embodiment, because a number of watertight outputs equal to 250 x 20 = 5000 cannot be easily achieved, it is possible to group the segments of the same radius according to a number of segments, depending on the value radius, on intermediate circles located at different depths, in order to reduce the number of exits. It is then possible to wear the elementary electrodes or the part of these which are connected together to a determined electrical potential, that of the anode shown in FIG. 2b in the case of an improved or optimized asymmetric chamber. One can thus obtain partial counting rates, functions of the value of the radius of the segments of the group considered. It is further possible to provide, at each sector with the same angular position, an vernier type analog reading system, as shown in FIGS. 5d and 5e. The analog reading system can consist, as shown in FIG. 5d, of two complementary bands in the shape of a right triangle Tl, T2 opposite by their hypoto- nude and placed symmetrically with respect to the bisector OB of the sector considered. The reading of the position value of radius r of the circular band, seat of an electric detection voltage, is given by the ratio of the value of the voltages detected at each complementary band. In an alternative embodiment shown in FIG. 5e, the two complementary bands in the shape of a triangle T'1, T'2 together occupy the entire surface of the circular sector with an angle of 18 °. In this case, the shape of the complementary strips can be chosen so that the position of the circular strip is given by the ratio of the value of the detected voltages. A fine calibration of the position, value of the radius, can be carried out.

Claims

1. Ionizing radiation gas detector, comprising, in a pressurized gas enclosure, means for absorbing said ionizing radiation making it possible to generate electrons from this ionizing radiation and means for amplification by avalanche phenomenon electronics of said electrons, characterized in that it comprises means for detecting and reading said electronic avalanches comprising at least: - a detection electrode having a plurality of elementary detection electrodes intended to detect the electric charge of said avalanches;

- An interfacing circuit electrically coupled to said detection electrode, this interfacing circuit comprising a plurality of detection outputs and making it possible to seal said gas enclosure.

2. Detector according to claim 1, characterized in that said interfacing circuit comprises a detection counter electrode having a plurality of elementary detection counter electrodes, each elementary detection counter electrode being electrostatically coupled to at least an elementary detection electrode, in order to allow the transmission of the detected electrical charge of said electronic avalanches with a view to their counting, said detection electrode and detection counter electrode making it possible to ensure gas tightness of said gas enclosure under pressure.

3. Detector according to claim 1 or 2, characterized in that said means for absorbing said ionizing radiation and said means for amplification by electronic avalanche phenomenon are formed by a chamber of wires of asymmetrical type, said detection electrode and elementary detection electrode forming a cathode electrode and elementary cathode electrodes respectively.

4. Detector according to claim 1 or 2, character- laughed in that said means for absorbing said ionizing radiation and said means for amplification by avalanche phenomenon are formed by a first, a second and a third planar parallel electrode, the third electrode distant from the second by a smaller distance at 200 μm constituting an anode electrode and forming said detection electrode constituted by elementary anodes.

5. Detector according to one of claims 2 to 4, characterized in that said detection electrode formed by said elementary detection electrodes and said detection counter electrode formed by said elementary detection counter electrodes are formed by at least one layer of electrically insulating material, blade with substantially parallel faces, a first face of said blade, placed inside said gas enclosure being provided with electrically conductive elements, each forming an elementary detection electrode, and a second face of said blade placed outside said gas enclosure being provided with electrically conductive elements each forming an elementary detection counter-electrode.

6. Detector according to one of claims 1 to 5, characterized in that said elementary detection electrodes and said elementary detection counter-electrodes are aligned in two orthogonal directions so as to allow two-dimensional tracking X, Y of said electronic avalanches.

7. Detector according to one of claims 1 to 6, characterized in that said elementary detection electrodes and said elementary detection counter-electrodes are constituted by zones of electrically conductive material of substantially square shape and aligned to form a checkerboard, two-dimensional detection matrix.

8. Detector according to claim 7, characterized in that the conductive zones of substantially shaped square are each subdivided into two triangular elements separated by a diagonal space, a triangular element on two successive triangular elements forming said elementary detection counter-electrodes in the direction of travel of one or the other two-dimensional direction being interconnected with a line counting assigned to one of the two-dimensional directions.

9. Detector according to one of claims 1 to 4, characterized in that said interfacing circuit is formed by a circuit of the multilayer printed circuit type, formed by a set of superimposed elementary layers, one of the faces of the printed circuit multilayer, oriented towards the interior of said gas enclosure comprising said detection electrode, each elementary layer comprising a plurality of interlayer electrical connections allowing the electrical connection of said elementary detection electrodes to another face of the multilayer printed circuit oriented the exterior of said gas enclosure, said electrical connections being impermeable to the gas contained in the gas enclosure.

10. Detector according to claims 6, 7 and 9, characterized in that the conductive zones of substantially square shape forming the elementary detection electrodes have a plane configuration in the plane X, Y of two-dimensional detection adapted to the corresponding plane dimension of said avalanches , which makes it possible to optimize the spatial resolution of the elementary detection electrodes placed on the face of the first elementary layer oriented towards the interior of said pressurized gas enclosure.

11. Detector according to claim 10, characterized in that said conductive zones are each formed by a plurality of concentric rings, each crown of even odd rank of the same conductive area being interconnected in parallel in the direction Z perpendicular to the directions X , Y detection two-dimensional, all of said crowns of even odd respectively even row being assigned to one respectively the other of said two-dimensional detection directions X, Y, which makes it possible to reduce the number of outputs while maintaining a high counting rate.

12. Detector according to claim 11, characterized in that, in the case of the detection of diffraction phenomena of LAUE, said rings are constituted by concentric circular zones.

13. Detector according to claim 12, characterized in that each circular area is subdivided into a plurality of identical segments, each segment corresponding to a determined counting capacity.

14. Detector according to one of claims 6 to 13, characterized in that, to each two-dimensional direction is assigned a given number of counting lines f X- to X _n }; f Y- to Y _n 1, each counting line being electrically connected to at least one conductive zone forming an elementary electrode respectively an elementary detection counter-electrode, all the counting lines assigned to each direction being provided with a device for Vernier-type detection of the row of the counting line subjected to the electrical charges of an electronic avalanche.