EP0340126B1 - Parallaxenfreier gasgefüllter Röntgenstrahlen-Detektor - Google Patents

Parallaxenfreier gasgefüllter Röntgenstrahlen-Detektor Download PDF

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Publication number
EP0340126B1
EP0340126B1 EP89420149A EP89420149A EP0340126B1 EP 0340126 B1 EP0340126 B1 EP 0340126B1 EP 89420149 A EP89420149 A EP 89420149A EP 89420149 A EP89420149 A EP 89420149A EP 0340126 B1 EP0340126 B1 EP 0340126B1
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EP
European Patent Office
Prior art keywords
electrodes
detector
input
sample
absorption
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP89420149A
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English (en)
French (fr)
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EP0340126A1 (de
Inventor
Vincent Comparat
Jean Ballon
Pierre Carrechio
Alain Pélissier
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Centre National de la Recherche Scientifique CNRS
Inel SAS
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Centre National de la Recherche Scientifique CNRS
Inel SAS
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    • 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
    • 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
    • H01J47/008—Drift detectors

Definitions

  • the invention relates to detectors of ionizing radiation, in particular X-rays, and more particularly gaseous detectors, that is to say those for which the material absorbing the radiations to generate electrons is a gas (based on argon or xenon for example) see the first part of claim 1.
  • the invention also relates to the use of such a detector.
  • This type of detector is used for example to analyze samples of matter (metal alloys, proteins, crystal structures, biological macromolecules etc.) in order to determine the structure.
  • the samples are placed in front of the detector and lit laterally (in general) by an X-ray source; they diffract the rays and return them to the detector and the role of the latter is to determine the angle of incidence at which it receives the X-rays, therefore the angle of diffraction by the sample.
  • the measured diffraction angles provide indications of the structure of the sample material.
  • FIG. 1 Known two-dimensional gas detectors have a structure which is generally represented in FIG. 1. They correspond for example to what is described in FIG. 1 of American patent US Pat. No. 4,595,834.
  • the detector comprises a sealed enclosure 10 containing the absorbent gas, and on the front face a sealed inlet window 12, transparent to X-rays.
  • This window carries a transparent electrode 14 brought to a potential V1.
  • V1 a potential
  • Between the window 12 and the bottom of the enclosure 10 extends the space 16 called absorption and drift space, filled with gas (argon or xenon with polyatomic additives).
  • an electron detector 18 At the bottom of the enclosure, opposite the window 12 is placed an electron detector 18 called “location detector” because of its function which is to detect the presence and the position of a packet of electrons from the ionization of the enclosure gas.
  • This detector 18 comprises an input electrode 19 transparent to the electrons brought to a potential V2 greater than V1 (for example 0V (volt) if V1 is at -4000V (volts) and the distance between the electrodes 14 and 19 is l '' order of 10 cm).
  • photonic radiation 24 is re-emitted from the sample towards the absorbing gas with an angle of incidence that one seeks to know.
  • a photon Upon entering the gas, a photon will be absorbed at a point in the enclosure and at this point it will emit an electron or a packet of electrons.
  • the electric field in the absorption and drift space is created by the potential difference V2 - V1 so that the electrons drift, along the field lines, towards the detector 18 and their arrival position is detected.
  • the field lines are straight lines perpendicular to the electrodes 14 and 19.
  • the electron detector 18 will detect a position a or b for receiving an electron packet .
  • the object of the present invention is to produce a two-dimensional radiation detector without parallax error.
  • a theoretical solution is simple: it would consist in making a spherical enclosure with a spherical input electrode and an electron detector with localization also spherical and concentric with the input electrode, the sample being placed in the center of these elements. spherical. The electrons are then entrained in the direction of the incident radiation. There is no parallax error.
  • Figure 2 of the aforementioned patent US-A-4,595,834 proposes to produce a radial electric field (that is to say spherical equipotentials) using a spherical input electrode, a spherical concentric auxiliary electrode, the space absorption and drift being delimited by these two electrodes, and a transfer space being provided between the spherical auxiliary electrode and the location detector which is planar.
  • the potential difference between the two electrodes creates a radial electric field and spherical equipotentials in the absorption space.
  • the spherical electrodes are difficult to produce, especially the auxiliary electrode because it must be very transparent to the electrons since the electrons must reach the localization detector; it is therefore produced in the form of a grid of fine wires which is difficult to manufacture.
  • the parallax error is reduced by forcing the X-rays to be absorbed near the spherical input electrode where the field is approximately radial. This is obtained by using xenon under high pressure and limits the use of such a system to not too energetic X-rays and requires the use of a fairly thick spherical beryllium window. For reasons of pressure resistance, this window is necessarily of limited size.
  • the present invention proposes a new X-ray detector which makes it possible to avoid the drawbacks of the gaseous detectors of the prior art and in particular authorizes the placement of a sample at a variable distance from the entry window, while minimizing the 'parallax error, and simplifying manufacturing.
  • a gaseous detector of radiations emitted by a sample comprising a closed enclosure containing an absorbent gas for the radiation, an entrance window transparent to the radiations to be detected, an absorption and drift space behind the entry window and, at the end of this space, a two-dimensional plane electron location detector to determine the coordinates of an electron arrival point generated by an impact of photons in the absorbent gas, the detector further comprising a group of input electrodes situated behind the input window and largely transparent to radiation; this detector further comprises a group of lateral electrodes surrounding the absorption and drift space, the individual input electrodes and the individual lateral electrodes being brought to potentials which are different from one another and which vary according to the position at which one wishes to place the sample relative to the entry window, the potentials chosen for each of the electrodes being such that the absorption and drift space is separated into two parts without the use of electrodes physically delimiting this separation , the equipotentials in the first part being spherical or quasi-spherical and centered
  • a distance between the entrance window and the detector sufficient, for example 10 cm, almost all of the X-rays will be absorbed in the first part and this at a pressure equal to or slightly higher than atmospheric pressure.
  • a much simpler construction detector is thus obtained, presenting no parallax error, and making it possible to place the sample to be observed at a variable distance from the input window.
  • the lateral electrodes of the enclosure will preferably be formed on conical side walls laterally delimiting the absorption and drift space.
  • the input electrodes are formed by screen printing on an insulating substrate and are separated from each other by a highly resistive substance allowing the flow of electric ionization charges which would risk accumulating between the electrodes.
  • the detector comprises a sealed external enclosure 30 closed at the front by an inlet window 32 transparent to X-rays (or more generally to the radiation to be detected).
  • the window is for example made of mylar or kapton (trademarks for polymer films) or beryllium.
  • the bottom of the enclosure 30 comprises, as in the prior art, a plane electron detector 34 which is a location detector, two-dimensional, for example a wire detector, with parallel plates or any other type of known gas detector.
  • a plane electron detector 34 which is a location detector, two-dimensional, for example a wire detector, with parallel plates or any other type of known gas detector.
  • a set of input electrodes which are in principle circular, concentric and all in the same plane, parallel to the plane of the electron detector. The fact that they are all in the same plan facilitates manufacturing but this is not an obligation. One can for example arrange them on a spherical surface.
  • These input electrodes are symbolized by the reference 36; they are best seen in plan view in FIG. 4.
  • the center of the circular input electrodes is located on the general axis 38 of the system, axis perpendicular to the electron detector 34 at its center.
  • the input electrodes 36 can be carried by a transparent X-ray support separate from the input window 32 or can be applied to the window, with the interposition of an insulating layer if the window is conductive.
  • the enclosure 30 is filled with gas absorbing the radiation to be detected: for example argon or xenon with one or more additives (hydrocarbon, CO2, etc.) allowing the localization detector 34 to function properly and having good drift characteristics and the absence of excessive electronic recombination which would harm the collection of electrons.
  • gas absorbing the radiation to be detected for example argon or xenon with one or more additives (hydrocarbon, CO2, etc.) allowing the localization detector 34 to function properly and having good drift characteristics and the absence of excessive electronic recombination which would harm the collection of electrons.
  • an absorption and drift space 40 is materially delimited, between the input electrodes 36 and the electron detector 34, by a side wall 42 of generally conical shape, having as axis the general axis 38 of the detector; this wall 42 surrounds the entire absorption and drift space in which electrons can be generated by incident radiation and then directed towards the electron detector 34.
  • the conical side wall 42 need not be sealed; it only serves as a support for lateral electrodes 44 which surround the drift and absorption space 40.
  • the wall 42 may for example be a sheet based on glass fiber on which are deposited conductors constituting the electrodes 44, for example by screen printing or by printed circuit techniques.
  • the individual input electrodes 36 and the lateral individual electrodes 44 can be brought to potentials which are all different from each other, these potentials being able to vary depending on the distance at which the sample 20 to be observed will be placed relative to the electrodes d 'entry 36.
  • the lateral electrodes 44 are distributed over the entire length of the wall 42, between the small end of the cone (immediately adjacent to the plane of the input electrodes) and the large end of the cone (immediately adjacent to the plane of the electron detector).
  • the lateral electrodes are circular, centered on the axis 38 of the detector.
  • the number of electrodes 36 and 44 is a function of the desired precision on the electric field inside the absorption and drift space.
  • the individual potentials of the side electrodes are brought by conductors 46 external to the wall 42, through conductive passages arranged in the wall opposite each electrode.
  • the outer conductors 46 are connected to connectors 48 through which the various potentials can be brought.
  • the potentials can be generated by resistive dividing bridges, not shown, located outside the enclosure 30 and preset as required for desired sample distances, or by a more complex voltage generation system controlled by outside by the detector user.
  • connection system is the same for the input electrodes 36 but it has not been shown so as not to make Figure 2 heavy.
  • a distance D is chosen at which the sample 20 to be observed will be placed (distance between the sample and the plane of the input electrodes 36) and the sphere centered on the position of the sample and of radius D is called SPHD.
  • the radial electric field is produced not only by virtue of the lateral electrodes 44 situated inside the SPHL sphere, but also by virtue of an appropriate choice of the potentials of the lateral electrodes 44 situated outside the SPHL sphere; this remark is important because the absence of a material spherical auxiliary electrode at the location of the limiting auxiliary sphere SPHL or the absence of plane auxiliary electrodes between regions A and B to simulate a spherical electrode, requires doing also pay particular attention to potentials applied to the lateral electrodes 44 located outside the SPHL limit sphere.
  • the spherical equipotentials in the vicinity of the limit sphere SPHL are in fact particularly sensitive to the proximity of the plane detector and they are not isolated by an electrostatic screen which until now constituted the auxiliary electrode or electrodes materially placed in the limit region between the regions A and B.
  • the equipotentials in region B are determined, by the method of electrical images, between a sphere SPHL brought to a constant potential VL and the plane of the detector 34, brought to a fixed potential VF; the electric field on the SPHL sphere is calculated as a function of VL and VF.
  • V (r) (VD - VL) x L x D / r (LD) + (L x VL - D x VD) / (LD)
  • FIG. 3 shows, in addition to the spherical equipotentials of region A, an intermediate equipotential EQB of region B, which is not a sphere centered on point S.
  • the distance D at which the sample to be observed can be changed, and this results in a new preferential distribution of potentials to be assigned to the input electrodes 36 and to the side electrodes 44. It is therefore possible to move the position of the sample while retaining spherical equipotentials, centered on the sample, in most of the absorption and drift space 40.
  • region A can go down to 70% of this distance.
  • FIG. 4 represents the configuration of the input electrodes 36. These are concentric conductive circular tracks. They are produced in this example by screen printing of a conductive paste of carbon (carbon having the advantage of being fairly transparent to X-rays) on an insulating support.
  • a conductive paste of carbon carbon having the advantage of being fairly transparent to X-rays
  • the individual electrodes are supplied by conductors located on the other side of the support.
  • the support is then pierced with holes 50 filled with conductive paste and the supply conductors 52 are electrically connected to these holes.
  • the supply conductors can be screen printed on the other side of the insulating support. They must be as transparent as possible to the radiation to be detected.
  • FIG. 5 represents the configuration of the input conductors seen in cross section perpendicular to the plane of the input window, through only one of the conductive passages 50 and along the supply conductor 52 which is connected to this hole.
  • the insulating support is designated by the reference 54.
  • a highly resistive paste 56 is deposited between the circular conductive tracks constituting the electrodes 36 intended to evacuate towards the electrodes 36 the electric charges (ions) which are liable to accumulate at the interface between the insulating substrate 54 and the gas. of the enclosure. These charges come from the ionization of the gas and disturb the shape of the equipotentials towards the input of the detector if they remain stored on the insulating substrate.
  • the highly resistive paste can be a paste based on carbon in small proportion in an insulating resin.
  • the conductive electrodes 36 are deposited directly (by screen printing for example) on a resistive substrate (highly resistive) and not insulating; the same result would be achieved with regard to the removal of troublesome loads.
  • the side electrodes 44 can be deposited by screen printing on a flexible insulating sheet constituting the side wall 42; this flexible sheet is then rolled up in the form of a truncated cone.
  • the electrodes can also be produced in flexible printed circuit or else by stacking circular electrodes spaced by insulating shims. The connections with the supply conductors will however always be outside the space 40 so as not to disturb the electric field on the inside of the side wall 42.
  • FIG. 6 shows a slightly different constitution of the detector, in which an attempt is made to analyze the rear X-ray diffraction, by a sample of material.
  • the detector to be traversed in its center by a pierced axial tube 60 through which an X-ray emission beam can pass, directed towards the sample 20.
  • the rays re-emitted towards the rear by the sample are captured and analyzed by the detector.
  • the walls of the tube 60 are also side walls of the absorption and drift space 42, and that they also carry individual side electrodes 44; these electrodes are brought to potentials which are calculated in the same way than the others both in the upper region and in the lower region of the enclosure.
  • connections to bring the potentials to the different electrodes along the tube are made with the same constraints as above, and it is also recommended to provide a resistive substance between the electrodes peripheral to the tube.

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  • Measurement Of Radiation (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Electron Tubes For Measurement (AREA)

Claims (10)

  1. Gasgefüllter Detektor für von einer Probe (20) abgegebene Strahlung, mit einer geschlossenen Kammer (30), die ein die Strahlung absorbierendes Gas enthält, mit einem für die zu detektierende Strahlung transparenten Eintrittsfenster (32), einem Absorptions- und Driftraum (40) hinter dem Eintrittsfenster und, am Ende dieses Raumes, mit einem ebenen zweidimensionalen Detektor (34) zur Lokalisation von Elektronen, um die Koordinaten eines Auftreffpunktes von Elektronen zu bestimmen, die durch einen Aufprall von Photonen in dem absorbierenden Gas erzeugt wurden, wobei der Detektor noch eine Gruppe von Eingangselektroden (36) aufweist, die hinter dem.Eintrittsfenster gelegen und weitgehend transparent für die Strahlung sind, dadurch gekennzeichnet, daß er darüberhinaus eine Gruppe von seitlichen Elektroden (44) enthält, die den Absorptions- und Driftraum umgeben, wobei die einzelnen Eingangselektroden (36) und die einzelnen seitlichen Elektroden (44) auf voneinander unterschiedlichen und als Funktion der Position, an der man die Probe in bezug zu dem Eintrittsfenster zu plazieren wünscht, variablen Potentialen gehalten werden, wobei die für jede der Elektroden gewählten Potentiale so sind, daß der Absorptions- und Driftraum in zwei Abteile ohne Verwendung von Elektroden, die diese Teilung materiell begrenzen, unterteilt ist, wobei die Äquipotentiale in dem ersten Abteil sphärisch oder quasi-sphärisch und um die Position der Probe zentriert sind und die Äquipotentiale in dem zweiten Abteil sich kontinuierlich ändern von einer sphärischen Form am Ort der Unterteilung bis zu einer ebenen Form in der unmittelbaren Nähe des ebenen Detektors für die Elektronen.
  2. Gasgefüllter Detektor nach Anspruch 1, dadurch gekennzeichnet, daß die seitlichen Elektroden (44) über die gesamte Distanz zwischen Eingangselektroden (36) und Detektor für die Elektronen (34) verteilt sind.
  3. Detektor nach einem der Ansprüche 1 oder 2, dadurch gekennzeichnet, daß das erste Abteil (A) des Absorptions- und Driftraumes sich über eine Distanz von ungefähr 70 bis 90 % der Distanz zwischen den Eingangselektroden (36) und dem Detektor für die Elektroden (34) erstreckt, wobei die Distanz in der Achse des Detektors gemessen wird.
  4. Verwendung eines gasgefüllten Detektors nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die Potentialwerte der verschiedenen Eingangselektroden und der verschiedenen seitlichen Elektroden nach dem folgenden Rechenverfahren bestimmt sind:
    a. Bestimmen der Äquipotentiale zwischen einer Strahlungskugel entsprechend der Distanz (L) zwischen der Probe und dem ersten der beiden Abteile des Absorptions- und Driftraumes mit dem Potential (VL) und einer konzentrischen Strahlungskugel entsprechend der Distanz (D) zwischen der Probe und dem Eintrittsfenster, die auf einem Potential (VD) gehalten wird,
    b. Festlegen des Potentiales der in dem ersten Abteil gelegenen Eingangselektroden (36) und seitlichen Elektroden (44) als Funktion dieser Bestimmung und
    c. Festlegen des Potentiales der in dem zweiten Abteil gelegenen Elektroden durch lineare Interpolation.
  5. Verwendung eines gasgefüllten Detektors nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die Potentialwerte der verschiedenen Eingangselektroden und der verschiedenen seitlichen Elektroden nach dem folgenden Rechenverfahren bestimmt sind:
    a. Bestimmen der Äquipotentiale zwischen einer Strahlungskugel entsprechend einer Distanz (L) zwischen der Probe und dem ersten der beiden Abteile des Absorptions- und Driftraumes, die auf dem Potential (VL) gehalten ist, und einer konzentrischen Strahlungskugel entsprechend der Distanz (D) zwischen der Probe und dem Eintrittsfenster, die auf einem Potential (VD) gehalten ist,
    b. Bestimmen der Äquipotentiale zwischen der auf einem Potential (VL) gehaltenen Kugel und einer auf einem Potential (VF) gehaltenen Ebene und
    c. Bestimmen der resultierenden Potentiale an den Orten, an denen die unterschiedlichen Elektroden plaziert sind, wobei die den verschiedenen Elektroden zugeteilten Potentiale die resultierenden Potentiale sind.
  6. Verwenden eines gasgefüllten Detektors nach Anspruch 5, dadurch gekennzeichnet, daß die Potentialwerte der unterschiedlichen Elektroden diejenigen sind, die aus einer zusätzlichen Berechnung resultieren, die darin besteht, das Potential (VL) derart zu wählen, daß das elektrische Feld in einem Punkt der auf dem Potential (VL) gehaltenen Kugel den gleichen Wert wie in der im Schritt a ausgeführten Rechnung und der in dem Schritt b ausgeführten Rechnung hat.
  7. Verwendung eines gasgefüllten Detektors nach einem der Ansprüche 4 bis 6, dadurch gekennzeichnet, daß die Potentiale an den Eingangselektroden und den seitlichen Elektroden durch ein iteratives, auf einem Rechner ausgeführten Rechenverfahren optimiert sind.
  8. Detektor nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß eine Substanz (56) mit hohem Widerstand zwischen den Eingangselektroden (36) angeordnet ist, um das Einlagern von elektrischen Ladungen zwischen zwei benachbarten Elektroden zu vermeiden.
  9. Detektor nach einem der Ansprüche 1 bis 3 und 8, dadurch gekennzeichnet, daß die seitlichen Elektroden (44) auf einer konischen Wand (42) gebildet sind, die den Absorptions- und Driftraum begrenzt.
  10. Detektor nach einem der Ansprüche 1 bis 3, 8 und 9, dadurch gekennzeichnet, daß er mit einem axialen Rohr (60) versehen ist, das ihn in seinem Zentrum durchquert, um die Beleuchtung einer Probe und die Beobachtung der Rückstreuung zu erlauben, wobei die seitlichen Elektroden (44) einheitlich längs der Wand des Rohres in dem Absorptions- und Driftraum verteilt sind.
EP89420149A 1988-04-27 1989-04-25 Parallaxenfreier gasgefüllter Röntgenstrahlen-Detektor Expired - Lifetime EP0340126B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8806018 1988-04-27
FR8806018A FR2630829A1 (fr) 1988-04-27 1988-04-27 Detecteur gazeux pour rayons-x sans parallaxe

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Publication Number Publication Date
EP0340126A1 EP0340126A1 (de) 1989-11-02
EP0340126B1 true EP0340126B1 (de) 1993-08-04

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EP89420149A Expired - Lifetime EP0340126B1 (de) 1988-04-27 1989-04-25 Parallaxenfreier gasgefüllter Röntgenstrahlen-Detektor

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US (1) US4954710A (de)
EP (1) EP0340126B1 (de)
JP (1) JPH02177243A (de)
DE (1) DE68907993T2 (de)
FR (1) FR2630829A1 (de)

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Publication number Priority date Publication date Assignee Title
FR2718633B1 (fr) * 1994-04-19 1996-07-12 Georges Charpak Dispositif d'imagerie médicale en rayonnement ionisant X ou gamma à faible dose.
US6198798B1 (en) * 1998-09-09 2001-03-06 European Organization For Nuclear Research Planispherical parallax-free X-ray imager based on the gas electron multiplier
SE0003390L (sv) * 2000-09-22 2002-03-23 Xcounter Ab Parallax-fri detektering av joniserande strålning
US8119978B2 (en) * 2006-07-10 2012-02-21 University Health Network Apparatus and methods for real-time verification of radiation therapy
US7639783B1 (en) 2008-06-02 2009-12-29 Bruker Axs, Inc. Parallax free and spark protected X-ray detector
WO2016191883A1 (en) 2015-06-05 2016-12-08 University Health Network Sensors with virtual spatial sensitivity for monitoring a radiation generating device

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Publication number Priority date Publication date Assignee Title
FR2363117A1 (fr) * 1976-08-26 1978-03-24 Anvar Perfectionnements aux dispositifs de detection et de localisation de rayonnements
US4595834A (en) * 1984-05-23 1986-06-17 Burns Ronald E Low parallax error radiation detector

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FR2630829A1 (fr) 1989-11-03
DE68907993D1 (de) 1993-09-09
US4954710A (en) 1990-09-04
DE68907993T2 (de) 1994-03-24
JPH02177243A (ja) 1990-07-10
EP0340126A1 (de) 1989-11-02

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