Radiation detector of very high performance

• US 6,011,265 A
• Filed: 10/22/1997
• Issued: 01/04/2000
• Est. Priority Date: 10/22/1997
• Status: Expired due to Term

• Current Assignee: European Organization for Nuclear Research
• Original Assignee: European Organization for Nuclear Research
• Inventors: Sauli, Fabio
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Israel, Andrew
• Application Number:
  US08/956,128
• Time in Patent Office: 804 Days
• Field of Search: 250/374, 250/385.1
• US Class Current: 250/374
• CPC Class Codes: H01J 47/02 Ionisation chambers

Abstract

A radiation detector in which primary electrons are released into a gas by ionizing radiations and drifted through an electric field to a collecting electrode for detection. It further includes a gas electron multiplier formed by one or several matrices of electric field condensing areas which are distributed within a solid surface perpendicular to the electric field. Each electric field condensing area consists of a tiny hole passing through the solid surface that forms a dipole adapted to produce a local electric field amplitude enhancement proper to generate an electron avalanche from one primary electron. The gas electron multiplier operates thus as an amplifier or a preamplifier within a host radiation detector.

Claims

1. A radiation detector in which primary electrons are released into a gas by ionizing radiations and are caused to drift to a collecting electrode by means of an electric field, said radiation detector including a gas electron multiplier comprising at least one matrix of electric field condensing areas, said electric field condensing areas being distributed within a solid surface which is substantially perpendicular to said to said electric field, each of said condensing areas producing a local electric field amplitude enhancement sufficient to generate in said gas an electron avalanche from one of said primary electrons so that said gas electron multiplier operates as an amplifier of a given gain for said primary electrons,

said matrix of electric field condensing areas comprising:

an insulator having first and second foil metal claddings on opposed faces thereof forming a sandwich structure;

a plurality of through holes traversing said sandwich structure; and

biasing means for developing a bias voltage potential which is applied to said first and second metal claddings so as to generate, at each of said through holes, one of said electric field condensing areas, and

said sandwich structure being disposed substantially perpendicular to said electric field, said first metal cladding forming an input face for said drift electrons and said second metal cladding forming an output face for any electron avalanche generated at each through hole forming one of said electric field condensing areas.

2. The radiation detector of claim 1, wherein said local electric field amplitude enhancement generated by each of said condensing local areas is substantially symmetrical in relation to an axis of symmetry of said condensing local area, so that said local electric field amplitude enhancement is at a maximum at the center of symmetry of said condensing local area.

3. The radiation detector of claim 1, wherein said electric field condensing areas are substantially identical in shape and regularly distributed within said solid surface so as to form said matrix.

4. The radiation detector of claim 1, wherein said through holes are substantially identical and circular in shape in viewed in a direction substantially perpendicular to said sandwich structure.

5. The radiation detector of claim 1, wherein each of said through holes is formed by first and second frusto-conical bored holes said first frusto-conical bored hole substantially extending from said first metal-cladding to an intermediate surface of said sandwich structure and said second frusto-conical bored hole substantially extending from said second metal-cladding to said intermediate surface of said sandwich structure, said first and second frusto-conical bored holes each comprising a first circular opening of a diameter of a first given value at the level of said input and output faces respectively to and a second circular opening of a diameter of a second given value, smaller than the first ones, said second circular opening of said first and second frusto-conical bored holes joining together at the level of said intermediate surface of said sandwich structure so as to form said bored-through hole.

6. The radiation detector of claim 1, wherein said through holes are identical in shape and regularly distributed over all of the metal clad faces of said insulator foil.

7. The radiation detector of claim 1, wherein said through holes are identical in shape and regularly distributed over a part of the metal clad faces of said insulator foil so as to form at least one blind detection zone for said radiation detector.

8. The radiation detector of claim 1, wherein said solid surface is a planar surface.

9. The radiation detector of claim 1, wherein said solid surface is spherical in shape.

10. The radiation detector of claim 1, wherein said solid surface is cylindrical in shape.

11. The radiation detector of claim 1, wherein said solid surface comprises adjacent elementary solid surfaces, each of said elementary solid surfaces forming thus one elementary gas electron multiplier comprising at least one matrix of electric field condensing area.

12. The radiation detector of claim 1, in which said collecting electrode is adapted to operate at unity gain, in an ionization mode, said collecting electrode at least comprising a plurality of elementary anodes allowing an electronic detection of each electron avalanche.

13. The radiation detector of claim 1, comprising a plurality of successive matrices of electric field condensing areas, said successive matrices being disposed parallel to one another to define homothetic matrices over a common center forming said gas electron multiplier and two successive matrices of said successive matrices being spaced apart from each other by a given separating distance in a direction parallel to said electric field forming a first electric field so as to define therebetween successive electric fields and to allow any electron of one electron avalanche to drift as a primary electron along said separating distance by means of its corresponding electric field so that said gas electron multiplier operates as an amplifier having a gain which is the product of the gain yield from each successive matrix.

14. The radiation detector of claim 1, wherein said collecting electrode comprises, on an insulator foil:

a first set of elementary anodes disposed on a first face of said insulator foil, said first face of said insulator foil and said first set of elementary anodes facing said gas electron multiplier, said first set of elementary anodes comprising a plurality of parallel electric conductive strips extending along a first given direction;

a second set of elementary anodes disposed on a second face of said insulator foil, said first and second sets of elementary anodes being separated by said insulator foil, said second set of elementary anodes comprising a plurality of parallel electric conductive strips extending along a given direction, transverse to said first given direction, and

said first and second sets of elementary anodes thereby enabling detection of said electron avalanche along said second and first directions, respectively, so as to form a bidirectional radiation detector.

15. In a radiation detector in which primary electrons are released into a gas by ionizing radiations, said radiation detector comprising a drift region from which said primary electrons are caused to drift by means of a substantially parallel electric field, a collection region, a gas electron multiplier located between said drift region and said collection region and comprising at least one matrix of electric field condensing areas, said electric field condensing areas being distributed within a solid surface which is substantially perpendicular to said parallel electric field, each of said condensing areas producing a local electric field amplitude enhancement to generate in said gas an electron avalanche from one of said primary electrons such that said gas electron multiplier operates as a preamplifier of given gain for said primary electrons upstream said collecting electrode of said radiation detector, and a collecting electrode for collecting from said collection region electrons produced by said electron avalanche, said matrix of electric field condensing areas comprising:

an insulator having first and second metal claddings on opposed faces thereof so as to form a planar sandwich structure;

a plurality of through holes extending transversely through said planar sandwich structure; and

biasing means for providing a bias voltage which is applied to said first and second metal claddings so as to generate at the level of each of said through holes one of said electric field condensing areas.

16. The gas electron multiplier of claim 15, wherein said local electric field amplitude enhancement generated by each of said condensing local areas is substantially symmetrical in relation to an axis of symmetry of said condensing local area which is perpendicular to said plane so that said local electric field amplitude enhancement is at a maximum at the center of symmetry of said condensing local area.

17. The gas electron multiplier of claim 15, comprising a plurality of successive matrices of electric field condensing areas, said successive matrices being disposed parallel to one another and two successive matrices of said successive matrices being spaced apart from each other by a given separating distance in a direction parallel to said parallel field forming a first parallel electric field so as to define therebetween successive electric fields and to allow any electron of one electron avalanche to drift as a primary electron along said separating distance by means of its corresponding parallel electric field such that said gas electron multiplier operates as a preamplifier the gain of which is the product of the gain yield from each successive matrix upstream of said collecting electrode of said radiation detector.

18. A radiation detector in which primary electrons are released into a gas by ionizing radiations, said radiation detector comprising a drift region from which said primary electrons are caused to drift by means of an electric field, a collection region, a gas electron multiplier located between said drift region and said collection region and comprising at least one matrix of electric field condensing areas, said electric field condensing areas being distributed within a solid surface which is substantially perpendicular to said electric field, and a collecting electrode for collecting electrons from said collection region said matrix of electric field condensing areas comprising:

an insulator having metal cladding on opposite faces thereof forming a sandwich structure; and

a plurality of through holes extending transversely through said sandwich structure, each of said through holes having an opening aperture diameter comprised between 20 μ

m and 100 μ

m.

19. The radiation detector of claim 18, wherein said insulator foil is made of a polymer material of thickness comprised between 25 μ

m and 500 μ

m, said through holes being spaced apart from one another at a distance comprised between 50 μ

m and 300 μ

m.

20. The radiation detector of claim 18, wherein each through hole of said plurality of through holes is provided with an internal lateral surface delimited by said insulator, said lateral surface comprising at least one local zone in which permanent electric charges are implanted, said permanent electric charges being distributed within said insulator and local zone thereof so as to further enhance and stabilize said electric field at the level of each corresponding electric field condensing area.

21. The radiation detector of claim 18, wherein each through hole of said plurality of through holes is provided with an internal lateral surface delimited by said insulator, said lateral surface comprising at least one local zone of electric conductivity comprised between 10¹⁵ and 10¹⁶ Ω

/square.

22. The radiation detector of claim 18, wherein each said through hole of said plurality of through holes has a cross section along a longitudinal plane of symmetry of said through hole which is conical in shape, each of said through holes comprising first and second circular openings of given values different from each other thereby forming first and second opening aperture diameters of different values, said radiation detector further comprising controllable direct and reverse biasing means for providing a direct biasing voltage and a reverse biasing voltage, respectively, which are applied to said first and second metal claddings so as to generate at the level of each of said through holes one of said electric field condensing areas which is thus functionally reversed.

23. A radiation detector for photons emitted by an external source, said radiation detector comprising, in a vessel containing a gas adapted to generate an electron avalanche from a primary electron through an electric field:

an inlet window having an inner face and a transparent electrode disposed on the inner face of said inlet window, said inlet window and transparent electrode being adapted to transmit said photons within said gas;

a photocathode layer facing said transparent electrode, said photocathode layer being adapted to generate one photo-electron as a primary electron under impingement of each one of said photons thereon;

a gas electron multiplier comprising at least one matrix of electric field condensing areas, said matrix of electric field condensing areas comprising;

first and second foil metal-clad insulators on opposed faces of said matrix comprising first and second metal claddings and first and second insulators, said photocathode layer being disposed on said first metal cladding so as to face said transparent electrode, said photocathode layer, and said first and second metal claddings, forming a sandwich structure with said first and second insulators, and

a plurality of through holes traversing said sandwich structure such that each of said through holes permits free flowing therethrough of the gas and any electrically charged particle generated therein;

first biasing means for maintaining said transparent electrode and first metal cladding substantially at the same voltage value so as to allow extraction of any photo-electron generated by said photocathode layer under impingement thereof of each one of said photons;

second biasing means for providing a bias voltage which is applied between said first and said second metal claddings, so as to form, at the level of each of said through holes, one of said electric field condensing areas in which a condensed electric field is generated so that said condensed electric field operates to convey each of said photo-electrons to one given electric field condensing area and to then generate from said photo-electron regarded as a primary electron one electron avalanche which is passed through said through hole forming said given electric field condensing area;

a collecting electrode comprising a plurality of elementary anodes, said collecting electrode facing said second metal cladding and being spaced apart therefrom, so as to define a detection region within said vessel; and

third biasing means for providing a bias voltage which is applied to said collecting electrode so as to allow the detection of said electron avalanche.

24. The radiation detector of claim 23, wherein said collecting electrode comprises, on an insulator foil:

a first set of elementary anodes disposed on a first face of said insulator foil, said first face of said insulator foil and said first set of elementary anodes facing said gas electron multiplier, said first set of elementary anodes comprising a plurality of parallel electric conductive strips extending along a first given direction

a second set of elementary anodes disposed on a second face of said insulator foil, said first and second sets of elementary anodes being thus separated by said insulator foil, said second set of elementary anodes comprising a plurality of parallel electric conductive strips extending along a given direction, transverse to said first given direction,

said first and second sets of elementary anodes thereby enabling detection of said electron avalanche along said second and first directions respectively so as to form a bidirectional radiation detector.

25. A radiation detector in which primary electrons are released into a gas by ionizing radiations, said radiation detector comprising a drift region from which the primary electrons are caused to drift by means of an electric field, a collection region, a gas electron multiplier located between said drift region and said collection region, said multiplier comprising a sandwich structure comprising an insulator having first and second conductive surfaces on opposite sides thereof and a plurality of through holes extending transversely through said sandwich structure to form a matrix of electric field condensing areas, each of said electric field condensing areas producing a local electric field amplitude enhancement sufficient to generate in said gas an electron avalanche from any of said primary electrons in said drift region and to transfer multiplied electrons into the collection region, and a collecting electrode for collecting from said collection region multiplied electrons produced by said electron avalanche.

26. A radiation detector in accordance with claim 25, wherein a plurality of gas electron multipliers are disposed between said drift region and said collecting electrode.