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
  • H01J47/02—Ionisation chambers
  • H01J47/026—Gas flow ionisation chambers

Definitions

• the present invention relates to an ionization chamber, a chain for measuring the activity of a gas emitting ⁇ radiation, which may for example be a tritium detection chamber, and a method of implementing the latter.
• a tritium chain with an ionization chamber is used to measure the activity of a gas emitting ⁇ radiation in a given gaseous atmosphere, by example that of a glove box, that of a laboratory ventilation network, or that of a nuclear chimney control.
• the ionization chamber which is immersed directly in the medium to be controlled, provides a current proportional to the activity to be quantified.
• a processing electronics allows to measure intensities between 10 "14 and 10 " 8 A.
• Such a measurement chain is composed of an ionization chamber, which acts as a detector, a preamplifier, a signal processing electronics, and a connection cable between the preamplifier and the electronics. treatment.
• Chambers with massive anode and cathode a chamber of this type, illustrated in FIG. 1, includes a central electrode 10 in nickel-plated brass forming an anode, a shell 11 in brass forming a cathode, a filling orifice 12, a nozzle 13 for adaptation to a preamplifier, a guard ring 14 in nickel-plated brass, insulators 15 in polystyrene , O-rings 16.
• Such chambers are used for measurements of low activities, for example less than 5,000 LDCA (admissible contamination limit). They are generally of large volume, for example around 10 000 cm 3 .
• Chambers with anode and / or with a light cathode a chamber of this type, illustrated in FIG. 2, comprises removable electrodes 20 and 21, namely a central anode 20 and a cathode 21 formed by a brass mesh, of copper or aluminum, and is provided with a filling orifice 22. It is arranged here in a steel shell 23, provided with two orifices 24 and 25 respectively for filling and evacuation. It further comprises an O-ring 26, a guard ring 27, polystyral insulators 28, an output 29 to a high voltage, and an output 30 to a preamplifier.
• Such chambers are dedicated to the measurement of higher activities (glove box, or even certain manufacturing processes). These are generally small volumes, for example 100 cm 3 .
• the use of light electrodes for the measurement of strong activities aims at limiting the contamination of surface of the electrodes which causes a significant background noise.
• a preamplifier mounted directly on the ionization chamber, makes it possible to amplify the current, which can have a very low value, at a sufficient level to make it transmissible by the connecting cable to the processing electronics.
• Electronics of the first type are said to be more precise because their drift over time is lower.
• Electronics of the second type are less delicate to implement and less expensive.
• the signal processing electronics must have a large measuring range (from 10 ⁇ 14 A to 10 "8 A or from 10 " 12 to 10 "6 A), which implies automatic switching of the ratings.
• Measuring systems of the known art have many drawbacks:
• the measurements are, in fact, more stable when the atmosphere in the vicinity of the room can be heated (stabilization in temperature, convection stirring, action on humidity ...);
• a complete measurement chain (detector + processing electronics + cable) has a cost between approximately 72 kF (approximately 14 kF for a 100 cm 3 detector and approximately 58 kF for electronics) and approximately 126 kF (approximately 68 kF for a 10,000 cm 3 detector and approximately 58 kF for electronics) .
• the present invention aims to overcome the drawbacks of these devices of the prior art.
• the present invention relates to a cylindrical ionization chamber comprising an anode formed by a central bar of electrically conductive material and a cathode of electrically conductive material surrounding said anode, both connected to two elements of a mechanical base of said chamber , characterized in that it comprises two cylindrical flanges made of non-magnetic and insulating material centered on the anode and arranged perpendicularly to the latter at its two ends, and in that the cathode is formed from a wire wound on the peripheral part of these two flanges.
• the lower end of the anode, and the two ends of the wire forming the cathode are connected to male plugs arranged on the lower flange.
• the base is provided at its two upper and lower ends respectively with a contact carrier assembly and a connector, said assembly comprising female plugs capable of receiving the male plugs arranged on the lower flange, and connected by conductive wires. to connector lugs, the chamber thus being removable.
• a cylindrical body for protecting the chamber is fixed to the upper part of the base.
• the present invention also relates to a chain for measuring the activity of a gas emitting ⁇ radiation comprising such an ionization chamber, a preamplification assembly mounted just behind the ionization chamber, an electronic remote signal processing and a connecting cable between the preamplifier assembly and the processing electronics.
• the preamplification assembly performs analog / digital conversion.
• the measurement chain can be, for example, a tritium measurement chain.
• the present invention also relates to a method for implementing this ionization chamber, such that one of the following three variants can be obtained, in which a heating current is circulated in the cathode:
• the temperature being higher than 400 ° C.
• Figures 1 and 2 illustrate two ionization chambers of the prior art.
• Figures 3 and 4 illustrate the ionization chamber of the invention.
• FIG. 5 illustrates the ionization chamber + preamplification assembly according to the invention.
• FIG. 6 illustrates comparative measurement curves obtained for an ionization chamber of the known art and for the ionization chamber of the invention.
• FIG. 7 illustrates the processing chain according to the invention.
• FIG. 8 illustrates an exemplary embodiment of the chain illustrated in FIG. 7.
• an ionization chamber 34 of cylindrical shape, comprises a central anode 35 formed by a bar made of electrically conductive material, for example made of stainless steel, two lower cylindrical flanges 36 and upper 37 made of an agnetic and insulating material, for example ceramic, PTFE or mixed material (ceramic + PTFE), centered on the anode 35 and arranged perpendicularly to the latter at its two ends, and a cathode 38 formed of a wire of conductive material, for example platinum, wound on the peripheral part of these two flanges 36 and 37, thereby surrounding the anode 35.
• these two flanges 36 and 37 are provided with three openings respectively 50 of circular shape, which has the advantage of lightening the structure and reducing the contaminable surface.
• the anode 35 at its lower end, is connected to a first male plug 39.
• the two ends of the wire forming the cathode 38 are connected to two other male plugs 39 arranged on the lower flange 36.
• FIG. 3 also illustrates a connector flange 41, forming a mechanical base, provided at its two upper and lower ends respectively a contact carrier assembly 40 and a connector 42.
• the assembly 40 comprises female plugs 47, for example four in number, capable of receiving the male plugs 39, for example four in number, arranged on the lower flange 36, and connected by conductive wires 49 to lugs of the connector 42, the chamber 34 thus being removable.
• a cylindrical protective body 43 On the upper part of the flange 41 is fixed a cylindrical protective body 43, which is disassembled in the measurement phases. Also shown are a ring 45 and a nut 44 allowing the fixing of the flanges 36 and 37 on the anode, an insulating barrel 46, a stainless steel coated seal 48.
• Flanges 36 and 37 allow background noise levels below 5.10 '14 A to be reached, which is essential for measuring low currents.
• the flanges 36 and 37 make it possible to no longer have to use a structure in guard rings to precisely delimit the lines of electric fields in the chamber.
• the wound cathode 38 made of extremely fine wire, for example 0.05 mm in diameter, makes it possible to divide by a certain number n, for example 16, the active surface of the chamber. Such a winding tends towards a notion of "immaterial electrode", which would obviously be ideal for eliminating surface contamination. The results obtained show a reduction in background noise due to surface contamination. In addition to the reliability of the measures which is improved, the cost of corrective maintenance is also minimized because the replacement of detectors becomes less frequent.
• cathode 38 is a nested series type winding allows three possibilities for implementing the ionization chamber:
• the self-supporting structure of the chamber 34 causes it to become a consumable element without the need to replace either the flange 41 or the associated connectors.
• the mechanical fixing functions of the chamber 34 on the base 41 and electrical continuity of the chamber 34 are provided by all of the male connectors 39 and female connectors 47.
• This solution is made possible by the extreme lightness of the chamber d ionization 34, which is for example 30 g.
• the cost of the ionization chamber according to the invention is approximately 7,000 F compared to 14,000 F of a 100 cm 3 chamber of the known art. Besides the fact that such rooms are replaced less often (low surface contamination), their cost is divided by approximately two, the corrective maintenance on them is therefore greatly reduced. “The flange 41 is tested for tightness, the system can therefore be mounted on a Tritium manufacturing process without jeopardizing its confinement.
• a preamplification assembly 51 can be mounted in the base 41 just behind the ionization chamber 34. It makes it possible to amplify and digitize the signal leaving said chamber.
• the activity measurement chain of gas emitting ⁇ radiation comprises an ionization chamber 34 such as described above, a preamplification assembly 51, a signal processing electronics 52 and a connection cable 53 between the preamplification assembly 51 and the processing electronics 52.
• the electronics 52 can be offset several meters of the assembly described in Figure 5.
• the processing electronics 52 includes several sets:
• a network interface for example BITBUS.
• the general functions provided by the preamplification unit 51 and the processing electronics 52 are as follows:
• FIG. 8 illustrates an exemplary embodiment of the circuits constituting the various elements of the chain, namely:
• the preamplification assembly 51 comprising an amplifier 56, an isolation amplifier 57, a 14 bit analog / digital converter 58, a temperature compensation resistance Rc, two resistors RI and R2 corresponding to two power supply positions of the cathode;
• the signal processing electronics 52 comprising:
• a power supply 61 which receives 220 V and which delivers 0 V, 5 V and ⁇ 12 V, • a central unit 62 which comprises for example a microprocessor ⁇ P, a RAM memory, an EPROM memory, and a PSTN unit,

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

Applications Claiming Priority (3)

Publications (2)

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• 1999
  • 1999-04-20 FR FR9904962A patent/FR2792772B1/fr not_active Expired - Lifetime
• 2000
  • 2000-04-18 US US09/958,041 patent/US6734433B1/en not_active Expired - Lifetime
  • 2000-04-18 WO PCT/FR2000/001001 patent/WO2000063948A1/fr not_active Ceased
  • 2000-04-18 EP EP00920825A patent/EP1171902B1/de not_active Expired - Lifetime
  • 2000-04-18 DE DE60020952T patent/DE60020952T2/de not_active Expired - Lifetime
  • 2000-04-18 CA CA2370992A patent/CA2370992C/fr not_active Expired - Lifetime
  • 2000-04-18 JP JP2000612983A patent/JP4584463B2/ja not_active Expired - Lifetime

Non-Patent Citations (1)

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