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
  • H01J47/06—Proportional counter tubes

Definitions

• the present invention relates to a gas detector for detecting ionizing radiation such as ⁇ , ⁇ , ⁇ radiation, or x or ultra violet radiation from a multitude of proportional microcounters assembled to form a proportional counter.
• Such a detector finds many applications in the fields of medical imaging, biology, particle physics, or even crystallography, and in many fields requiring non-destructive testing.
• the detector of the invention is of the type in which primary electrons resulting from the ionization of radiation by the gas are multiplied under the effect of an electric field of high local intensity, in a gas.
• the parallel plate detector comprises a counter produced by means of two parallel grids spaced from each other by a few millimeters and between which the multiplication of the electrons takes place. This area between the two parallel grids is called "multiplication zone".
• the multiplication zone of such a detector therefore takes the form of a single volume delimited by the two grids.
• the counters of these parallel plate detectors can only have a limited spatial resolution and, because of the plate / grid thickness, they cannot be arranged so as to constitute detectors of various shapes.
• the wire detector comprises a plurality of equidistant wires, stretched in a plane. On either side of this plane are placed two taut grids forming cathodes. The multiplication of electrons takes place near the wires since there is a high electric field there. However, the multiplication zone of such a detector cannot be isotropic; furthermore, it does not allow the detector to have various shapes.
• microstrip detector Another more recent type of gas detector is the microstrip detector.
• the counter In this microstrip detector, the counter consists of coplanar electrodes etched on an insulating support. Such a microstrip detector is described in French patent FR-A-2 602 058.
• the major drawback of this detector is its relatively low gain which is limited substantially to 5000 since it does not allow several counters to be superimposed.
• the counters of these microstrip detectors have amstrop multiplication zones, located on very fine tracks (approximately 10 ⁇ , which makes them very sensitive to slamming. These detectors also have the disadvantage of being relatively fragile.
• the object of the present invention is precisely to remedy the drawbacks of the various detectors described above. To this end, it offers a gas detector comprising a counter consisting of a plurality of independent proportional microcounters.
• the invention relates to an ionizing radiation detector comprising an enclosure filled with a gaseous mixture which may comprise, for example a rare gas, inside which is arranged a proportional counter which delimits, between itself and the upper wall of the enclosure, an area in which ionization of the gas occurs by absorption of radiation.
• This proportional counter further comprises at least one lower electrode and at least one upper electrode, parallel with each other, separated from each other by a layer of insulating material and brought to different potentials.
• the upper electrode and the layer of insulating material comprise at least one breakthrough in which a substantially uniform electric field prevails and constituting a zone for the multiplication of the electrons resulting from the ionization of the radiation.
• Each portion of the meter comprising an upper electrode part and a pierced insulating layer part as well as a lower electro ⁇ e part constitutes an independent microcounter, also called an elementary cell.
• the lower electrode is an anode and the upper electrode is a cathode.
• the insulating material is a rigid material which can either be photosensitive, which makes it possible to facilitate the manufacture of the detector, or is highly resistive (with a resistivity of the order of 10 9 to 10 13 ⁇ .cirO, or fluorescent, which makes it possible to transform the UV radiation resulting from the multiplication into visible radiation.
• the proportional counter comprises a plurality of upper electrodes arranged one above the other, in a plane parallel to the lower electrode and separated from each other by a layer of material insulating material, the openings in each upper electrode being aligned with the openings in the layers of insulating material.
• the proportional counter comprises: a plurality of upper electrodes arranged in the same first plane, with the same first direction and connected to each other; and a plurality of lower electrodes arranged in the same second plane, parallel to the first plane, in the same second direction and connected to each other.
• the proportional counter has a generally cylindrical shape, the lower and upper electrodes forming an open cylinder traversed longitudinally by an electric wire for supplying potential.
• the upper electrode and the lower electrode are independent and each connected to a input of an electronic processing circuit, to form a pixel detector.
• FIG. 1A represents a perspective view of a detector of the invention comprising a proportional counter produced according to a first embodiment
• - Figure 1B shows a front view of a strip of microcounters according to the embodiment of Figure 1A;
• FIG. 2A shows a front view of a strip of microcounters according to a second embodiment of the invention
• FIG. 2B represents a perspective view of a counter produced with several strips of microcounters in FIG. 2A;
• FIG. 4 shows a front view of a set of microcounters in which several cathodes are superimposed;
• - Figure 5 shows a front view of a counter in which several strips of microcounters are superimposed;
• FIG. 6 represents a micrometer plate on which each micrometer is connected by its anode to an external circuit;
• FIG. 7 shows an example of arrangement of several bands of proportional microcounters;
• FIG. 8 represents an example of a cylindrical proportional counter;
• FIG. 9 shows a spectrum representative of the resolution for measuring an energy of 6 Kev coming from a source of Fe * - ⁇ , by a gas detector according to the invention.
• a gas detector according to the invention is shown diagrammatically.
• This detector comprises an enclosure 1 shown in phantom in the figure.
• This enclosure 1 is filled with a gaseous mixture which generally comprises a rare gas (such as argon, krypton, xenon, etc.) and which is subjected to a selected pressure.
• a gaseous mixture which generally comprises a rare gas (such as argon, krypton, xenon, etc.) and which is subjected to a selected pressure.
• This gas mixture ensures the absorption of the radiation received by the detector.
• These radiations are therefore ionized by the gas in a zone called "absorption zone", in which a weak and uniform electric field prevails. This ionization of radiation creates electric charges that we seek to multiply, thanks to the proportional counter 2.
• This proportional counter 2 comprises a multitude of microcounters (also called “elementary cells") referenced 4. Each of these microcounters 4 is produced by means of two electrodes located in different planes and brought to different potentials so as to create an electric field which attracts electrical charges from the ionization of radiation in the gas.
• the microcounters are arranged in strips 3 of microcounters.
• microcounters arranged in bands (or rows).
• these microcounters can be arranged according to all kinds of geometries (for example, in squares), but that they can also be independent. This choice of representation in "band” is simply intended to facilitate the understanding of the appended figures.
• each strip 3 of microcomputer comprises an upper electrode 5, namely a cathode, a lower electrode 6, namely an anode, and a layer of insulating material 7 situated between the two electrodes 5 and 6.
• the cathode 5 and the insulating layer 7 are perforated by openings 8 leading to the anode 6.
• Each opening 8 constitutes a multiplication zone.
• each microcomputer comprises a cathode portion 5, an insulating layer portion 7, an anode portion 6 and a multiplication zone 8.
• each strip 3 can have several openings 8, each microcounter 4 is independent since it has its own multiplication zone.
• a counter 2 of the invention can include a multitude of multiplication zones, which greatly limits the risks of breakdown.
• FIG. 1A there is shown "a cutaway" of the counter 2 which makes it possible to see two breakthroughs 8 belonging to the strips 3 of microcounters and leading to the respective ⁇ anodes.
• FIG. 1B shows more precisely a strip 3 of microcounters.
• this strip 3 comprises an upper electrode 5 and a lower electrode 6.
• the electrode upper 5 is a cathode and the lower electrode 6 is an anode.
• the cathode 5 and the anode 6 are separated from each other by a layer 7 of an insulating material.
• this insulating material is also photosensitive, which makes it easier to manufacture the detector.
• the insulating material is also highly resistive. According to yet another embodiment, the insulating material is fluorescent so as to transform the UV radiation due to the multiplication into visible radiation which can, for example, be counted.
• the cathode 5, as well as the insulating layer 7, are pierced with holes 8 inside which an electric field prevails, which creates multiplication zones.
• the electric field is intense and almost uniform. It is therefore naturally towards these multiplication zones that the electric charges created by the ionization of the radiation in the absorption zone are directed.
• the cathode can be increased to a few hundred volts, so as to attract the primary charges and the anode brought to an even higher voltage, so as to ensure the multiplication of these primary charges.
• a substrate such as ceramic in order to ensure a better solidity of the counter.
• FIG. 2A there is shown, in section, microcounters 4 produced according to an embodiment different from that shown in FIG. 1B.
• the cathodes and the anodes are arranged in two perpendicular directions: the cathodes 5 are arranged in rows and the anodes 6 are arranged in rows.
• Each breakthrough 8 leads to a ⁇ anode, as in the previous embodiment.
• a proportional counter 2 is shown, produced by means of a multitude of strips 3 of microcounters of the type of that represented in FIG. 2A.
• the proportional counter 2 shown in this FIG. 2B comprises a plurality of cathodes 5 arranged in rows and a plurality of anodes 6 arranged in columns.
• the cathodes 5 are separated from the anodes 6 by a layer 7 of insulating, rigid and photosensitive material.
• the cathodes 5 as well as the layer of insulating material 7 are perforated by openings 8, which open onto the anodes 6, as shown in FIG. 2B.
• Such an arrangement of the electrodes 5 and 6 makes it possible to carry out the coding of events in two directions. It can therefore be, for example, used in imagery.
• the openings 8 of the microcounters 4 have been presented in this figure 2B as holes of round section.
• these microcounters may have openings 8 (or obviously) of different shapes.
• these recesses can be slots, parallel or non-parallel to each other; they can be conical, cylindrical, etc., and of variable size.
• Figures 3A and 3B show two examples of these recesses.
• the recess 8 has a conical shape which has the advantage of avoiding that the ions resulting from the multiplication adhere to the wall 8 ′ of the recess, that is to say to the material 7.
• the recess 8 of the microcounter has a concave wall 8 ′, the advantage of which is similar to that of the recess in FIG. 3A.
• the ratio between the solid part of a microcomputer and the hollowed part of this microcomputer is typically chosen between 1 and 10.
• the recesses are circular holes whose ratio between the depth of the hole and the width of the hole generally varies between 3 and 1/2.
• the light emitted during the multiplication can be collected to form images or to perform counting or to obtain a synchronization signal signaling the event (namely the avalanche of ions) .
• the strip 3 comprises two cathodes 5a and 5b and two layers 7a and 7b of photosensitive insulating materials: the insulating layer 7a is disposed between the cathodes 5a and 5b, and the insulating layer 7b is disposed between the cathode 5b and the common anode 6.
• the openings 8 are made throughout the thickness consisting of the cathodes and the insulating layers.
• Such an assembly with several stages of cathodes makes it possible to increase the height of the openings 8 and, consequently, the volume of the multiplication zone.
• the multiplication power of this zone is thus increased and the collection of the ions created during the multiplication is facilitated and increased.
• FIG. 5 there is shown a front view of a multistage counter produced by means of several plates 3a, 3b, of microcounters superposed one above the other.
• the microcounters are arranged in the form of strips substantially of the type shown in FIG. 1B.
• Each plate can either be placed directly on the lower plate or separated from its neighboring plate by gas identical to that prevailing in the activation zone (as is the case in this figure) or by an insulating layer.
• the anode 6a, 6b of each of the plates 3a, 3b has a breakthrough 8a, 8b aligned with the breakthroughs of the cathodes 5a, 5b and the insulating layers 7a, 7b and leading to an additional anode 6c.
• additional anodes 6c are necessary to ensure the creation of the electric field over the entire height of the openings and are placed under the clearance produced by the openings 8a and 8b. All of these plates 3a, 3b and additional anodes 6c are deposited on a rigid substrate 10.
• each cathode / anode space of a plate 3 has a lower multiplication power than a multiplication zone of the counter of FIG. 2A, the superposition of several cathode / anode spaces makes it possible to obtain a gain which is higher than in a simple multiplication zone (like those shown in Figure 2A).
• This "sandwich" configuration makes it possible to significantly reduce the electric field in the insulation; it also allows additional cathodes to collect part of the ions from the multiplication. The counting rate of the detector is thus greatly increased.
• each microcomputer 4 has its own multiplication zone 8. This means that each microcomputer is independent. However, in certain applications the microcounters 4 can be linked together, either via their cathode or via their anode.
• FIG. 6 there is shown a plate 3 of microcounters whose microcounters 4 are connected by their anodes 6 to an external circuit. More specifically, the plate 3 is bonded to a support 13 carrying the anodes 6 of the microcounters 4. Each anode 6 is connected by means of tracks PI, P2, from contact to the external circuit, for example, to an amplifier 15 itself arranged on a support 17. According to this example, the tracks PI and P2 pass through the support 13. Furthermore, as shown in this FIG. 6, a voltage source 19 is connected to the plate 3 by the cathode 5.
• each of them can be connected directly to a separate amplifier.
• Each microcomputer can then be considered as the pixel of a linear or two-dimensional detector.
• the invention thus has the advantage of facilitating the connection by the fact that this can be done either on the cathode side or on the anode side, so still on the back of the detector.
• the connecting tracks between the microcounters and the amplifiers can be engraved or screen printed during the manufacture of the proportional counter, so as to further facilitate the connection.
• each microcomputer makes it possible to give an electrical signal, a function of the quantity of electrons received.
• This electrical signal can be used for energy measurement and for measuring the position of impact. More precisely, the positioning of the impact of the ray (or spatial location) can be obtained directly by identifying the microcomputer affected, in the case where the absorption zone is weak. Otherwise, the electrons from the ionization are scattered on at least part of the proportional counter. We can then proceed to the search for the centroid, that is to say the microcomputer which has received the largest share of the scattered electrons.
• centroid among the affected microcounters one can use either a known logical method which consists in digitizing the signal derived by the affected microcounters and then calculating the corresponding centroid, or by an analogical method by taking the electrical signals on lines to delay type RC, LC or R. Whatever the method chosen for determining the location of events, it is necessary to carry out a processing of the signals coming from the cathode, of the signals coming from the anode and, for certain embodiments using a additional anode, signals from this additional anode.
• FIG. 7 there is shown another embodiment of the invention in which several strips 3a, 3b, 3c, 3d, 3e of microcounters are arranged to form a series of U and inverse U's. These bands are of the type of those shown in Figure 1B.
• This particular arrangement makes it possible to produce a delay line such as one can use to effect the localization of events.
• the different cathodes 5a-5e are juxtaposed perpendicular to each other other. Each of these cathodes 5a-5e corresponds to an anode 6a-6e separated from its corresponding cathode 5a-5e, by a layer of insulating material l a-le.
• FIG. 8 yet another embodiment of a proportional counter according to the invention is shown. Unlike the linear counters described in the previous embodiments, this proportional counter 2 is cylindrical. Such a cylindrical counter can be used, for example, in crystallography.
• this counter 2 has the form of an open cylinder whose opening 12 ensures the introduction of radiation inside the cylinder.
• This counter 2 therefore comprises a cathode plane 5 forming the interior wall of the cylinder and an anode plane 6 forming the exterior wall of the cylinder.
• the anode 6 and the cathode 5 are separated by a layer 7 of insulating and photosensitive material.
• This cylinder having been shown in section, we see on the section of said cylinder breakthroughs 8. Such breakthroughs 8 are distributed over the entire length of the cylinder; they are shown in dotted lines, since they are covered by the anode 6. As can be seen in FIG.
• an electric wire which 9 crosses the cylinder longitudinally this electric wire making it possible to bring a certain potential inside the cylinder. For example, one could bring the cathode 5 to a zero potential, the anode 6 to a potential of +1000 volts and the electric wire 9 to a potential of -200 volts.
• each set of microcounters is therefore produced by means of a sheet of insulating material covered on each of its faces with a material driver.
• the insulator may be glass or else photosensitive glass or even any other plastic material having sufficient dielectric strength.
• To make each of the microcounters on a plate it is necessary to pierce the composite sheet (insulating sheet covered on either side with a conductive layer) of blind holes.
• various known techniques can be used: - one of the methods consists in carrying out reserves in the cathode by photoengraving, then in digging it, for example by chemical attack. The cathode then serves as a self-supporting mask.
• the insulating sheet is pierced either by UV photogravure, by deep X-ray lithography or by chemical attack, laser machining, ion attack, etc. according to the nature of this insulating sheet;
• Another method consists in drilling blind holes directly using a laser capable of piercing the cathode and insulating it without piercing the anode.
• the anode will be chosen thicker than the cathode, or else in a material of an appropriate nature.
• the multiplier zones have a geometry such that it ensures the non-existence of breakdown between the electrodes, even at the ends of the plates, since the electrodes, cathodes and anodes are not in the same plane.
• the anodes being of simple and robust form, they are not subject to deterioration under the effect of possible breakdown or the electronic and ionic bombardment which they undergo.
• proportional meters described in FIGS. 1A to 8 can be used in gas detectors to determine different types of radiation.
• X-ray detectors used in crystallography
• the counters are placed on goniometers, in front of X sources or in front of synchrotron radiation sources.
• These detectors having a good resolution in energy and a significant gain, they make it possible to obtain a very good spatial resolution while simplifying the connection since the anode or cathode planes can comprise, by screen printing, all the necessary electrical paths towards external circuits.
• FIG. 9 a spectrum is shown showing the resolution of the energy measurements, for an energy of six thousand electron volts, in an argon / CO 2 mixture under atmospheric pressure.
• the multiplication gain obtained can be around 20,000, which ensures completely correct processing of electrical signals.
• the spatial resolution is of the order of 50 ⁇ m.
• Such a proportional counter advantageously makes it possible to withstand high counting rates by microcounters; this rate can be around 100,000 events per second.
• the counters according to the invention can have a high density of microcounters, this makes it possible to work with very high flows.
• each microcomputer is independent, it is possible to obtain an even higher signal, to allow the detection of weak fluxes, by operating the counters in Geiger regime.

Landscapes

• Measurement Of Radiation (AREA)
• Electron Tubes For Measurement (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=9469160

Family Applications (1)

Country Status (7)

Families Citing this family (42)

Family Cites Families (9)

• 1994
  • 1994-11-25 FR FR9414158A patent/FR2727525B1/fr not_active Expired - Lifetime
• 1995
  • 1995-11-23 WO PCT/FR1995/001548 patent/WO1996017373A1/fr active IP Right Grant
  • 1995-11-23 EP EP95941134A patent/EP0742954B1/de not_active Expired - Lifetime
  • 1995-11-23 US US08/676,222 patent/US5742061A/en not_active Expired - Lifetime
  • 1995-11-23 DE DE69529605T patent/DE69529605T2/de not_active Expired - Lifetime
  • 1995-11-23 CA CA002181913A patent/CA2181913C/en not_active Expired - Lifetime
  • 1995-11-23 JP JP51832596A patent/JP3822239B2/ja not_active Expired - Lifetime

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events