Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J47/00—Tubes for determining the presence, intensity, density or energy of radiation or particles
  • H01J47/02—Ionisation chambers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J47/00—Tubes for determining the presence, intensity, density or energy of radiation or particles
  • H01J47/06—Proportional counter tubes
  • H01J47/062—Multiwire proportional counter tubes

Definitions

• 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.
• a type of xenon pressure chamber of 3 bars has also been used for ⁇ 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 ⁇ ppl ⁇ 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.
• 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.
• FIGS. 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;
• FIG. 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
• FIG. 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.
• 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.
• the gas enclosure bears the reference E.
• 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.
• Fes a so-called top window
• Fes a so-called top window
• 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.
• 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.
• 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 .
• 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.
• 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 ⁇ m 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.
• 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 ⁇ m.
• These parameters allow counting rates greater than or equal to 10 7 c / s .mm 2 to be obtained.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 ⁇ m.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the elementary detection counter-electrodes 32i 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.
• X the number of conductors
• Y the number of the chamber
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the distance p separating two successive elementary detection electrodes, respectively two counter-electrodes of successive elementary detection can be taken equal to 100 ⁇ m, and the value of dimension c or side of each conductive zone can be taken equal to 1 mm.
• 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 ⁇ m for example, distance separating the grid G from the detection electrode 31, the dimension D has the value substantially 200 ⁇ m 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the electrical connections are impermeable to the gas contained in the gas enclosure.
• planar configuration of the elementary detection electrodes 31i it is thus indicated as shown in FIG.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 ⁇ m separated by intervals of 50 ⁇ m 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.
• a room with a 25 cm x 25 cm square interface circuit it is possible to obtain, as shown in FIG.
• FIGS. 4a, 4b and 4c appear 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 ⁇ m for example and that the dimension D of the avalanche is of the order of 200 ⁇ m also.
• 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.
• 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 diffraction pattern corresponds to a single series of concentric circular spots.
• 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 ⁇ m, for an accuracy of the order of 100 ⁇ m.
• the multilayer structure, as shown in Figures 4a to 4c, can then be advantageously used, so as to have a strip output.
• 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.
• 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.
• 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.
• 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.
• the crown patterns as shown in FIG. 5c, retain the general shape of the circular sectors, with an opening angle of 18 °.
• 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.
• 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 °.
• 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.

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• 1996
  • 1996-10-02 FR FR9612004A patent/FR2754068B1/fr not_active Expired - Fee Related
• 1997
  • 1997-10-01 WO PCT/FR1997/001736 patent/WO1998014981A1/fr not_active Application Discontinuation
  • 1997-10-01 EP EP97943923A patent/EP0929908A1/de not_active Withdrawn

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