EP0619597B1 - Ionisationskammer mit hoher Empfindlichkeit für Gammastrahlung - Google Patents

Ionisationskammer mit hoher Empfindlichkeit für Gammastrahlung Download PDF

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Publication number
EP0619597B1
EP0619597B1 EP19940400716 EP94400716A EP0619597B1 EP 0619597 B1 EP0619597 B1 EP 0619597B1 EP 19940400716 EP19940400716 EP 19940400716 EP 94400716 A EP94400716 A EP 94400716A EP 0619597 B1 EP0619597 B1 EP 0619597B1
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EP
European Patent Office
Prior art keywords
ionization chamber
enclosure
curve
electrodes
energy
Prior art date
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
Application number
EP19940400716
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English (en)
French (fr)
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EP0619597A1 (de
Inventor
Gilles Bignan
Jean Cloue
Alain Le Peron
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Orano Cycle SA
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Original Assignee
Commissariat a lEnergie Atomique CEA
Compagnie Generale des Matieres Nucleaires SA
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Publication date
Application filed by Commissariat a lEnergie Atomique CEA, Compagnie Generale des Matieres Nucleaires SA filed Critical Commissariat a lEnergie Atomique CEA
Publication of EP0619597A1 publication Critical patent/EP0619597A1/de
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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 high-efficiency ionization chamber for detecting ⁇ (gamma) radiation. It finds applications in the fields of nuclear reactors and nuclear fuel reprocessing plants.
  • the sources of ⁇ radiation generally used are sources of Cesium or sources of Cobalt. From this in fact, the ⁇ radiation to be detected has an energy of approximately 661 kev for a source of Cesium and approximately 1,170 to 1,300 kev for a source of Cobalt. The energy range of the ⁇ radiation to be detected is therefore between 500 and 1,500 kev.
  • background noise is very often present during these ⁇ radiation measurements.
  • This background noise is, in the case of reprocessing plants, the consequence of the ⁇ rays diffused from the dissolution solution. In the case of a nuclear reactor installation, this background noise is due to the various activation products of the medium considered.
  • the energy of such background noise is of the order of 80 to 100 kev.
  • One of these types is an ionization chamber comprising cylindrical housings filled with air at atmospheric pressure in which the application of a high voltage to a central electrode makes it possible to obtain an electric field, thanks to which electrons created by the ionization of air are collected on the electrode.
  • Such an ionization chamber (which is also more generally called a ⁇ detector) has only a low detection efficiency; its detection efficiency being of the order of 10 -9 A / Gy / h (amperes per absorbed dose of ⁇ radiation per hour) when a cobalt source is used as a source of ⁇ radiation.
  • Another type of ionization chamber consists of a cylindrical enclosure made of stainless steel and filled with Xenon brought to a pressure of 7 bars. This chamber has two cylindrical and coaxial electrodes arranged in the enclosure. These electrodes are electrically isolated and create an electric field between them. The passage of ionizing particles in this electric field produces ions which are collected by the electrodes.
  • Such a chamber has a detection efficiency of ⁇ radiation of approximately 5.10 -8 A / Gy / h for a Cobalt source.
  • the energy response curve C1 represented on a logarithmic scale in the appended FIG. 1, exhibits a maximum efficiency around 100 kev, which is explained, essentially, by the large effective cross-section of ionization of Xenon in the photoelectric domain from 50 to 400 kev of gamma / matter interaction.
  • an efficiency ratio Re is the ratio of the useful signal corresponding to an energy of the ⁇ rays of between 500 and 1,500 kev on the background noise which corresponds to an energy of the ⁇ rays of l '' from 80 to 100 kev
  • the object of the present invention is precisely to remedy the drawbacks mentioned above and to enable the efficiency ratio to be increased considerably.
  • the gas filling the enclosure is Argon brought to a pressure of between substantially 5 and 10 bars.
  • the enclosure has an outer wall made of Aluminum and covered, on its inner face, with a layer of Lead capable of absorbing photons of energy less than 100 kev.
  • This chamber is substantially identical to that described in the prior art. However, the materials used for its production and the gas filling said ionization chamber differ from those usually used.
  • This ionization chamber therefore comprises, as in the prior art, an enclosure 1.
  • this enclosure 1 is made of Aluminum.
  • the inner wall 2 of this enclosure 1 is covered with a layer of Lead, the thickness of which can vary from substantially 0.5 mm to 1 mm.
  • This enclosure 1 is filled with Argon under a pressure which can be approximately 5 to 10 bars.
  • This ionization chamber further comprises two electrodes: the high voltage electrode referenced 3 and the central electrode referenced 4. These electrodes 3 and 4 are cylindrical and coaxial.
  • the central electrode 4 is supported by an electrode support 5.
  • the high-voltage electrode 3 (or HT electrode) is supported by three electrode supports arranged 120 degrees from one another relative to the support 5 central.
  • the ionization chamber being represented in a sectional view, only two of these high-voltage electrode supports 3 are shown in FIG. 2.
  • These HT electrode supports 3 are referenced 6a and 6b. As their name suggests, these electrode supports 5, 6a and 6b make it possible to maintain the respective electrodes 4 and 3 in a fixed position inside the enclosure 1.
  • Electrode supports 5, 6a and 6b are made of conductive materials covered with an insulating material.
  • the support 5 and one of the supports 6 of the HT electrode 3 can be connected to an electrical source via a connection means introduced into the threaded base 15 of the enclosure 1.
  • This connection means thus that the electrical source is not shown in this figure for the sake of simplification of FIG. 2.
  • it is the support 6b which is connected to the electrical source.
  • This support 6b of the high voltage electrode 3 is therefore connected to the electrical source via the connection wire 7 and the connection pin 8 as well as the connection means introduced into the threaded base 15.
  • the support 5 of the central electrode 4 is connected, via the connection wire 9, to a pin of central connection 10 itself connected to the electrical source by the connection wire 11 and by the connection pin 12.
  • This ionization chamber further comprises a socket 13 allowing the enclosure 1 to be filled with gas, that is to say with Argon.
  • This queusot 13 is connected to the central pin 10 by a ground wire, said queusot 13 itself being grounded.
  • This set of connection pins, connection wires, sockets and electrode supports are included in the base, referenced 14, of the ionization chamber.
  • This base 14 is mounted on the enclosure 1 and has on its surface the screw pitch constituting the threaded base 15 and making it possible to fix the whole of the ionization chamber on the medium whose ⁇ radiation is sought to be detected, that is to say, for example, on the hot branch of a pressurized water reactor.
  • the electrodes 4 and 3 thus connected to an electrical source, can be brought to a voltage such that a direct potential difference is established between the central electrode 4 and the high voltage electrode 3.
  • An electric field E s' then establishes between these electrodes in the volume of gas which is located between said electrodes, this volume of gas being called the useful volume.
  • the incident radiation ⁇ which passes through this detector ionizes the Argon located in the enclosure 1, and therefore releases electrical charges which are collected by the electrodes 3 and 4. More precisely, the ions released by the particles ionizers crossing the Argon go either to the high voltage electrode 3 or to the central electrode 4 depending on the sign of their charge.
  • FIG. 3 there is shown the curve C2 of the energy response of an ionization chamber made of a material identical to that described in the prior art, that is to say an ionization chamber comprising a stainless steel enclosure; but this enclosure is filled with Argon.
  • the curve C2 which is represented on a logarithmic scale, like all the curves of Figures 1, 3, 4 and 5, aims to show the advantage of an enclosure filled with Argon compared to the enclosure of the prior art filled with Xenon.
  • the energy response curve of the ionization chamber of the prior art is referenced C1 and corresponds to the curve C1 shown in FIG. 1.
  • the curve C2 is therefore the energy response curve of an ionization chamber made of stainless steel and filled with Argon.
  • the gases used are respectively under a pressure of 7 bars (for the curve C1) and 9 bars (for the curve C2).
  • the gas used in the invention to fill the enclosure 1, namely Argon is a gas which does not have a particularly strong intrinsic efficiency; "intrinsic efficiency” means the efficiency from the point of view of creating the number of electrons.
  • Argon is a gas which optimizes the RE efficiency ratio between the energy range from 500 to 1,500 kev representing the useful signal, and the average energy from 80 to 100 kev representing the parasitic signal, c is the background noise.
  • the Argon is brought to a pressure ranging from 5 to 10 bars.
  • the Argon is brought to a pressure of 9 bars.
  • using Argon in a room ionization provides a contribution of radiation at 80-100 kev much lower than the contribution of radiation at 80-100 kev produced by the ionization chamber of the prior art.
  • the detection efficiency of the chamber d ionization relative to the curve C2 is of the order of 3.10 -8 A / Gy / h.
  • the detection efficiency represented on the curve C2 is equivalent to approximately 1.5 ⁇ 10 -8 A / Gy / h.
  • FIG. 4 the energy response curves of an ionization chamber are shown, the enclosure of which, filled with Xenon, is covered on its inner wall with a layer of Lead of, respectively, 0.5 and 1 mm thick.
  • the curve C1 represents the energy response curve of the ionization chamber of the prior art, that is to say the ionization chamber filled with Xenon and whose enclosure is made in Stainless steel.
  • Curve C3 represents the energy response curve of an ionization chamber filled with Xenon and whose enclosure is made of Aluminum covered on its inner face with a layer of 0.5 mm of Lead.
  • Curve C4 represents an energy response curve of an ionization chamber, the enclosure of which is filled with Xenon and made of coated Aluminum, on its face, inside of a layer of Lead 1 mm thick.
  • this embodiment of the enclosure 1 does not substantially modify the contribution of the ⁇ radiation of energy included in the range 500 to 1,500 kev, that is to say that it hardly modifies the number of electrons created, lead having the characteristic of absorbing photons whose energy is less than 100 kev.
  • the useful signal is substantially equivalent to the value of the useful signal of the curve C1, that is to say 5.10 -8 A / Gy / h, and that the background noise signal is substantially 3.10 -7 A / Gy / h.
  • the useful signal is substantially equivalent to the value of the useful signal of the curve C1, namely 5.10 -8 A / Gy / h, and that the noise signal background equals approximately 1.5.10 -7 A / Gy / h.
  • FIG. 5 shows the energy response curves of the ionization chamber of the prior art, and of ionization chambers according to the invention, in which the lead layer of the enclosure 1 is, 0.5 mm and 1 mm thick, respectively.
  • the curve C1 represents, as in FIGS. 1, 3 and 4, the energy response curve of the ionization chamber of the prior art.
  • Curve C5 represents the energy response of an ionization chamber according to the invention in which the enclosure 1 is covered, on its inner face, with a lead layer 0.5 mm thick.
  • curve C6 represents the energy response of an ionization chamber according to the invention, the enclosure of which is covered with a layer of Lead 1 mm thick.
  • the values of the useful signals and of the background noise signals of the curves C5 and C6 can be read. More precisely, the useful signal is substantially the same for the curve C5 and for the curve C6; it has a value of approximately 1.5.10 -8 A / Gy / h.
  • the background noise signal from curve C5 is approximately 6.10 -9 A / Gy / h and the background noise signal from curve C6 is approximately 2.10 -9 A / Gy / h.
  • Such an ionization chamber with such a gain in useful signal / background noise signal ratio, makes it possible, with equivalent measurement accuracy, to use sources of ⁇ radiation of lower intensity than that usually used; which consequently results in a lower cost of measurement stations by gammadensitometry.

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

Claims (3)

  1. Ionisationskammer für die Detektion von γ-Strahlung, umfassend:
    - einen Behälter (1), gefüllt mit Gas, und
    - zwei Elektroden (3, 4), im Innern des Behälters befindlich, wobei diese Elektroden elektrisch isoliert und von einander getrennt sind, um zwischen sich ein elektrisches Feld (E) zu erzeugen und in diesem elektrischen Feld den Durchgang von ionisierenden, Ionen erzeugenden Teilchen zu ermöglichen, die durch die genannten Elektroden eingefangen werden können,
    dadurch gekennzeichnet,
    daß das den Behälter füllende Gas Argon unter einem im wesentlichen zwischen 5 und 10 Bar enthaltenen Druck ist.
  2. Ionisationskammer nach Anspruch 1,
    dadurch gekennzeichnet, daß der Behälter eine aus Aluminium hergestellt Wand umfaßt.
  3. Ionisationskammer nach Anspruch 2,
    dadurch gekennzeichnet, daß die Wand auf einer Innenseite (2) von einer Bleischicht bedeckt ist.
EP19940400716 1993-04-07 1994-04-01 Ionisationskammer mit hoher Empfindlichkeit für Gammastrahlung Expired - Lifetime EP0619597B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9304118 1993-04-07
FR9304118A FR2703790B1 (fr) 1993-04-07 1993-04-07 Chambre d'ionisation à haute efficacité de détection de rayonnement.

Publications (2)

Publication Number Publication Date
EP0619597A1 EP0619597A1 (de) 1994-10-12
EP0619597B1 true EP0619597B1 (de) 1997-01-08

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EP19940400716 Expired - Lifetime EP0619597B1 (de) 1993-04-07 1994-04-01 Ionisationskammer mit hoher Empfindlichkeit für Gammastrahlung

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EP (1) EP0619597B1 (de)
JP (1) JPH075267A (de)
DE (1) DE69401374T2 (de)
FR (1) FR2703790B1 (de)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100866888B1 (ko) * 2006-10-04 2008-11-04 한국원자력연구원 와이어 수집 전극 및 이온 챔버 내 혼합 가압 기체를이용한, 감도가 향상된 철판 두께 측정용 방사선 센서 및측정 방법
US9312109B2 (en) * 2013-01-25 2016-04-12 General Electric Company High pressure ion chamber enclosure support mount

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2530381A1 (fr) * 1982-07-13 1984-01-20 Commissariat Energie Atomique Chambre d'ionisation pour la mesure de rayonnements gamma de haute energie
FR2631121B1 (fr) * 1988-05-03 1991-02-15 Commissariat Energie Atomique Dispositif de controle du taux de dissolution d'un residu nucleaire dans une solution de dissolveur

Also Published As

Publication number Publication date
JPH075267A (ja) 1995-01-10
DE69401374D1 (de) 1997-02-20
FR2703790B1 (fr) 1995-05-24
DE69401374T2 (de) 1997-06-26
FR2703790A1 (fr) 1994-10-14
EP0619597A1 (de) 1994-10-12

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