EP0029758B1 - Gasionisationsdetektor und einen solchen Detektor verwendendes Tomographiegerät - Google Patents

Gasionisationsdetektor und einen solchen Detektor verwendendes Tomographiegerät Download PDF

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Publication number
EP0029758B1
EP0029758B1 EP80401481A EP80401481A EP0029758B1 EP 0029758 B1 EP0029758 B1 EP 0029758B1 EP 80401481 A EP80401481 A EP 80401481A EP 80401481 A EP80401481 A EP 80401481A EP 0029758 B1 EP0029758 B1 EP 0029758B1
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EP
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Prior art keywords
electrodes
gas
detector according
compartments
compartment
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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
Application number
EP80401481A
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English (en)
French (fr)
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EP0029758A1 (de
Inventor
Rémy Klausz
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Thales SA
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Thomson CSF SA
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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
    • H01J47/02—Ionisation chambers

Definitions

  • the present invention relates to a gas ionization detector, according to the preamble of claim 1 which can be advantageously used in a CT scanner.
  • a detector is known from FR-A-2344121.
  • Detectors of this type use ionization chambers as described in FR-A-2 292 985 for example.
  • These ionization chambers consist of a sealed enclosure provided with a window permeable to the beam of ionizing radiation (X or y rays), inside this enclosure being placed metal plates, or electrodes, substantially parallel to each other. and perpendicular to the window, these electrodes being brought to potentials of determined values so as to establish between two successive electrodes a high electric field (several thousand volts / cm) and as uniform as possible.
  • a gas of high atomic number is introduced into the sealed enclosure under high pressure so that the beam of ionizing radiation penetrating into this enclosure ionizes the gas which it contains, thus releasing ions and electrons which are respectively collected by the electrodes.
  • the electric field lines generally have deformations at the ends of the electrodes, these deformations being due to the overflow of the electric field at the ends of the electrodes and to the presence of the entry window, placed in the vicinity of these, as is known from FR-A-2 348 567.
  • part of the electrical charges is not collected by the electrodes, which decreases the efficiency of the detector and can also create parasitic currents.
  • the electric fields undergo deformations such that the ions and / or the electrons produced in the space included between the collecting electrodes and the window cannot be collected by these electrodes and therefore do not contribute to the electrical signal delivered to the output of the detector.
  • the detector It is therefore necessary for the detector to be provided with a device serving both as a collimator and as a guard electrode, without affecting the performance of this detector.
  • One solution is to have a guard electrode in the extension of each of the measurement electrodes placed in the ionization chamber, the guard electrode being at the same potential as the electrode which it extends, so as to eliminate the deforma - tlons of the electric field.
  • guard electrodes are in the same enclosure they will collect charged particles (ions or electrons), which will decrease the efficiency of the detector, and, if these guard electrodes are placed outside the ionization chamber, the distance separating the guard electrode from the corresponding measurement electrode will be very important because of the thickness of the window which must withstand a significant pressure difference, which will lead to significant overflows of the electric field.
  • the detector object of the present invention avoids these drawbacks.
  • a gas ionization detector for detecting a beam of ionizing radiation, comprising a sealed enclosure forming an ionization chamber containing a gas, in this enclosure being arranged at least two measuring electrodes, and, in the extension of these measurement electrodes, two guard electrodes, these measurement electrodes being brought respectively to a first potential and to a second potential and the guard electrodes being brought respectively to the potential of the measurement electrodes which they extend, is characterized in that the enclosure is divided in leaktight manner into at least two compartments by means of a partition placed substantially perpendicular to the path of the beam, this partition being of dielectric material, permeable to the beam of ionizing radiation, these compartments being arranged at the one after the other on the beam path, in that the measuring electrodes are arranged in the front compartment al and the guard electrodes in the upstream compartment.
  • the detector with ionization chambers of known type shown in FIG. 1, comprises an enclosure C o into which is introduced, under high pressure, a gas of high atomic number.
  • This enclosure is provided with a window f permeable to the beam F of ionizing radiation (X-rays in the example described).
  • the detector according to the invention shown in FIG. 2, avoids these drawbacks.
  • This detector shown in FIG. 2, comprises a sealed enclosure C provided with a window f.
  • This enclosure C is divided into two compartments Ci and C 2 by means of a partition M of electrically insulating material, permeable to the beam of ionizing radiation (X-rays) and arranged substantially perpendicular to the beam F of X-rays.
  • X-rays ionizing radiation
  • measuring electrodes e 1 , e 2 , e i ... are arranged opposite each other. Two electrodes successive are separated from each other by determined distances.
  • Figure 3 shows a detail of figure 2.
  • the electrodes e 1 and e 21 are brought to the same first potential v 1 and the electrodes e 2 and e 22 are brought to the same second potential v 2 .
  • the potential v 1 is for example a negative HT potential of several thousand volts relative to the mass (to which the enclosure is connected for example) and the potential v 2 is then a positive potential, to ground for example, or equal to a few tens of volts for example relative to this mass.
  • a high pressure gas whose atomic number is of low value (hydrogen or helium for example) while a gas of high atomic number (xenon for example) is introduced, substantially at the same pressure , in the downstream compartment Ci.
  • the X-ray beam F crosses the window f and successively enters the upstream compartment C 2 which has, for the X-ray beam, a gas partition of very low attenuation, then in the downstream compartment Ci where the lines of strength of the electric field E remain perpendicular to the electrodes e 1 , e 2 ... without undergoing deformations, the guard electrodes e 21 , e 22 ... being very close to the main electrodes e 1 , e 2 ... corresponding, since the partition M which separates them is very thin (1/10 of a mm for example).
  • the guard electrodes form an anti-diffusion grid.
  • a measuring device A 1 is placed in the electrical circuit of the electrode e 2 for example, supplying a signal 1 2 corresponding to the current collected by this electrode e 2 .
  • the detector according to the invention allows measurements to be made for X-ray beam energies of different values.
  • the detector according to the invention may have more than two successive compartments, namely a downstream compartment Ci and several upstream compartments C 2 , C 3 ... (FIG. 4) separated from each other by partitions M 1 , M2 of small thicknesses.
  • partitions M 1 , M2 of small thicknesses.
  • electrodes e 21 , e 22 and e 31 , e 32 are respectively arranged.
  • the electrodes e 21 and e 31 are at the same potential as the electrode e 1 that they extend and the electrodes e 22 , e 32 are at the same potential as the electrode e 2 that they extend.
  • Electrodes e 21 , e 22 ; e 31 , e 32 are such that the absorption of X-rays, which is of low value, is located in the middle zone of the inter-electrode space.
  • the gases introduced into the different compartments C 1 , C 2 , C 3 are at the same pressure and have different atomic numbers, the atomic number of the gas introduced into the compartment Ci being the highest.
  • a measuring device A 1 is placed for example in the circuit of the electrode e 2 . Measuring devices A 2 , A 3 can also be placed in the circuits of electrodes e22 and e 32 .
  • This system comprises a tube T, twice bent, the ends 1 and 2 of which open respectively in the compartments Ci and C 2 .
  • a transverse wall 3 which can move on either side of a medium position, allows the pressures of the gases contained in the compartments C 1 and C 2 to be balanced.
  • This wall 3 can be a deformable membrane fixed to the tubing T or a piston for example.
  • Such detectors can advantageously be used in CT-type translation-rotation or in pure rotation CT ( Figure 6).

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  • Measurement Of Radiation (AREA)
  • Electron Tubes For Measurement (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Apparatus For Radiation Diagnosis (AREA)

Claims (10)

1. Gasionisationsdetektor zur Feststellung eines ionisierenden Strahlungsbündels (F), mit einem dichten, eine ein Gas enthaltende lonisationskammer bildenden Raum (C)., wobei in diesem Raum wenigstens zwei Meßelektroden (e1, e2) angeordnet sind und, in Verlängerung dieser Meßelektroden wenigstens zwei Schutz- bzw. Wächterelektroden (e21, e22), wobei diese Meßelektroden jeweils auf ein erstes Potential und ein zweites Potential gebracht werden und die Schutzelektroden jeweils auf das Potential der Meßelektroden, die sie verlängern, gebracht werden, dadurch gekennzeichnet, daß der Raum (C) abgedichtet in wenigstens zwei Kammern (C1, C2) mittels einer im wesentlichen senkrecht zur Bahn des Bündels angeordneten Trennwand (M) unterteilt ist, wobei diese Trennwand (M) aus dielektrischem für das ionisierende Strahlungsbündel durchlässigem Material besteht und diese Kammern (C1, C2) eine auf die andere folgend in der Bahn des Bündels angeordnet sind ; und daß die Meßelektroden (e1, e2...) in der abströmseitigen Kammer (C1) und die Schutzelektroden (e21, e22..) in der anströmseitigen Kammer (C2) angeordnet sind.
2. Gasionisationsdetektor nach Anspruch 1, dadurch gekennzeichnet, daß die in die anströmseitige Kammer (C2) und die abströmseitige Kammer (C1) eingeführten Gase im wesentlichen den gleichen Druck haben.
3. Gasionisationsdetektor nach Anspruch 2, dadurch gekennzeichnet, daß die in die anströmseitige Kammer (C2) und die abströmseitige Kammer (C1) eingeführten Gase von unterschiedlicher Atomzahl sind, wobei das in die anströmseitige Kammer (C2) eingeführte Gas über die niedrigere Atomzahl verfügt.
4. Gasionisationsdetektor nach Anspruch 1, dadurch gekennzeichnet, daß der Raum dicht in n-Kammern (C1, C2, C3) unterteilt ist, wobei n eine ganze Zahl größer 3 ist, und daß in diesen Kammern (C1, C2, C3...) jeweils Paare von Elek- troden (e1, e2; e21, e22 ; e31, e32) angeordnet sind, daß n-1 Schutzelektroden (e21 und e31 ; e22 und e32) in der Verlängerung jeder Meßelektrode (ei, e2) der Elektrodenpaare angeordnet sind und auf das gleiche Potential wie diese Elektrode (e1) gebracht sind ; und daß die in die n Kammern (C1, C2, C3) eingeführten Gase den gleichen Druck haben.
5. Gasionisationsdetektor nach Anspruch 4, dadurch gekennzeichnet, daß die jeweils in die n-1 anströmseitigen Kammern (C2, C3) eingeführten Gase Atomzahlen kleiner der Atomzahl des Gases haben, das in die abströmseitige Kammer (C1) eingeführt ist.
6. Gasionisationsdetektor nach einem der Ansprüche 1-4, dadurch gekennzeichnet, daß ein Druckausgleichssystem der in den verschiedenen Kammern des dichten Raums enthaltenen Gase diesem dichten Raum zugeordnet ist.
7. Gasionisationsdetektor nach Anspruch 6, dadurch gekennzeichnet, daß das Ausgleichssystem wenigstens ein zweimal gekrümmtes bzw. umgelenktes Rohrstück (T) aufweist, dessen Enden (1, 2) jeweils in die beiden Kammern (C1, C2) sich öffnen, in deren Innerem die Drücke der Gase auszugleichen sind ; und daß eine dichte und bewegliche Wand (3) das Rohrstück (T) quer in zwei Teile unterteilt.
8. Gasionisationsdetektor nach Anspruch 7, dadurch gekennzeichnet, daß die bewegliche Wand (3) eine nachgiebige verformbare Membran ist.
9. Gasionisationsdetektor nach Anspruch 7, dadurch gekennzeichnet, daß die bewegliche Wand (3) aus einem Kolben besteht.
10. Tomodensitometer, dadurch gekennzeichnet, daß es einen Gasionisationsdetektor nach einem der Ansprüche 1-9 umfaßt.
EP80401481A 1979-11-14 1980-10-17 Gasionisationsdetektor und einen solchen Detektor verwendendes Tomographiegerät Expired EP0029758B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR7928041 1979-11-14
FR7928041A FR2469797A1 (fr) 1979-11-14 1979-11-14 Detecteur a ionisation gazeuse et tomodensitometre utilisant un tel detecteur

Publications (2)

Publication Number Publication Date
EP0029758A1 EP0029758A1 (de) 1981-06-03
EP0029758B1 true EP0029758B1 (de) 1983-04-20

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EP80401481A Expired EP0029758B1 (de) 1979-11-14 1980-10-17 Gasionisationsdetektor und einen solchen Detektor verwendendes Tomographiegerät

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US (1) US4367409A (de)
EP (1) EP0029758B1 (de)
DE (1) DE3062841D1 (de)
FR (1) FR2469797A1 (de)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2504278B1 (fr) * 1981-04-15 1985-11-08 Commissariat Energie Atomique Detecteur de rayons x
US4980904A (en) * 1985-11-15 1990-12-25 Picker International, Inc. Radiation imaging calibration
US4751391A (en) * 1986-12-19 1988-06-14 General Electric Company High resolution X-ray collimator/detector system having reduced sensitivity to leakage radiation
DE4340389C1 (de) * 1993-11-26 1994-11-03 Siemens Ag Gasdetektor für die Computertomographie
DE4342779C1 (de) * 1993-12-15 1994-11-17 Siemens Ag Gasdetektor für die Computertomographie
RU180521U1 (ru) * 2017-04-28 2018-06-15 Федеральное государственное бюджетное учреждение "Петербургский институт ядерной физики им. Б.П. Константинова" Ионизационная камера
US11841104B2 (en) 2020-04-21 2023-12-12 Shanghai United Imaging Healthcare Co., Ltd. System and method for equalizing pressure in ionization chamber of radiation device
CN113749682B (zh) * 2021-08-05 2023-05-09 中国人民解放军总医院 具有隔断平台的扫描床

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1046235A (en) * 1963-08-23 1966-10-19 English Electric Co Ltd Radiation detectors
US4158774A (en) * 1975-08-01 1979-06-19 Stokes Arthur J Radiation detector with improved performance characteristics
DE2609626A1 (de) * 1976-03-09 1977-09-15 Philips Patentverwaltung Strahlennachweisvorrichtung
US4075527A (en) * 1976-09-27 1978-02-21 General Electric Company X-ray detector
NL7703944A (en) * 1977-04-12 1978-10-16 Philips Nv Multichannel X=ray detector esp. for computer tomography - has cells of differing measuring capacity increasing speed and accuracy
DE2747872A1 (de) * 1977-10-26 1979-05-03 Philips Patentverwaltung Strahlennachweisvorrichtung

Also Published As

Publication number Publication date
DE3062841D1 (en) 1983-05-26
EP0029758A1 (de) 1981-06-03
FR2469797B1 (de) 1981-10-30
FR2469797A1 (fr) 1981-05-22
US4367409A (en) 1983-01-04

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