EP1202322A1 - Detector for detecting electrically neutral particles, especially neutrons, using a gas-filled housing - Google Patents

Abstract

The detector has a detector housing (10) with detector gas, at least one converter (22) that produces a conversion product by absorbing the particles to be detected, whereby the conversion products produce electrically charge particles in the detector gas, at least one readout device (19) for detecting charged particles and at least one drift field generator (18) for producing a field that causes charged particles to drift to the read-out device. Independent claims are also included for the following: a converter for a detector, a method of manufacturing a converter and a detection method for detecting electrically neutral particles, especially neutrons.

Description

The invention relates to a detector for detecting electrically neutral particles according to claim 1, a converter device for a detector for detection Electrically neutral particles according to claim 11, a manufacturing method for a converter device according to claim 13 and a detection method for Detection of electrically neutral particles according to claim 14.

The use of low-energy neutron radiation, so-called thermal and cold neutrons, represents an important method in science (e.g. physical, chemical, biological and medical applications) and technology (e.g. non-destructive material testing). It is fundamental for all areas of application in science and technology the evidence, i.e. the detection of such neutrons, whereby detectors or Detection methods for neutrons have been a major economic in recent decades Have gained importance. The detection of neutrons can be made physical reasons only through a nuclear reaction of the same with a so-called Neutron converter can be realized. The neutrons of captured or absorbed the atomic nuclei of the converter, these nuclei then spontaneously decay. The mostly energy-rich resulting from the decay and electrically charged fragments, commonly called conversion products can then be called due to their ionizing effect be detected.

The gas helium-3, whose atomic nuclei consist of two protons and one neutron, has mainly been used to detect neutrons. This helium isotope is added to the actual counting gas of the detector in predetermined amounts in so-called gas detectors. Neutrons to be detected are absorbed by the helium-3 nuclei, which subsequently decay spontaneously in accordance with the nuclear reaction ³ He + ¹ n → ³ H + ¹ p + 764 keV, the tritium nucleus receiving a quarter and the proton three-quarters of the reaction energy. As high-energy, charged particles, these conversion products have an ionizing effect on the counting gas of such a gas detector. When neutrons are detected using helium-3 gas detectors, the conversion products in the counting gas thus generate charged particles, in particular free electrons. By applying an electrical drift field, these primary electrons are led to the electrodes of a readout structure. Appropriate shaping of the readout structure means that the electric field in the vicinity of the electrodes is so high that the primary charge can be enormously increased with the help of secondary gas ionization processes (gas amplification). The total charge generated in this way is subsequently collected on the electrodes and fed to an electronic evaluation device via a preamplifier.

Such neutron detectors in the form of conventional gas detectors with helium-3 as a neutron converter, however, have considerable disadvantages. In order to achieve an attractive detection efficiency of e.g. about 50% for thermal neutrons with a gaseous neutron converter such as helium-3 and at the same time to be able to determine the location of the impact of the neutrons, such detectors must be operated at a gas pressure of 5 to 10 bar. Due to the high operating pressure, this requires complex and expensive pressure vessels. A detection of neutrons over large detection areas can only be realized with the aid of large, matrix-like detector arrangements, which consist of a large number of small individual detectors, due to the design restrictions of the pressure vessels. For example, the IN5 neutron spectrometer from the Laue-Langevin Institute in Grenoble has 1400 individual helium-3 neutron detectors for angle-resolved neutron detection (cf. "The yellowbook guide to neutron research facilities at ILL", Institut Laue-Langevin, Grenoble, December 1997). However, the spatial resolution of approximately 2 cm × 10 cm and the typical acceptance of count rates of 10,000 detected neutrons per second and cm ² of such a neutron detector are very unsatisfactory.

The poor resolution and the low count rate acceptance can be improved by a combination of helium-3 as a converter with a so-called microstrip detector (MSGC) to approx. 2 mm x 2 mm and one million neutrons per second and cm ² (see Vellettaz et al., "Two-dimensional gaseous microstrip detector for thermal neutrons", Nuclear Instruments and Methods A 392 (1997), pages 73 to 79). However, because of the high gas pressure, even with a detector area of only 100 mm × 100 mm, these detectors are very complex and expensive to construct. Furthermore, the MSGC technology has proven to be very susceptible to interference.

Neutron scintillation detectors are also known for the detection of neutrons. With such detectors, a fixed neutron converter becomes a fixed one or liquid scintillator, for example in the form of a fine powder (see G.B. Spector et al., "Advances in terbium-doped, lithium-loaded scintillator glas development ", Nuclear Instruments and Methods A 326 (1993), pages 526 to 530). The conversion products used in a neutron detection reaction arise, deposit their energy in the scintillator. That from The scintillator then emits light that is then location-sensitive with a suitable one Detected light detection system. Such detectors are typical Detection efficiencies from 20% to 40%. However, the problem is Detection of the scintillation light. Because such detection concepts are a comparative one high sensitivity to X-rays and gamma radiation possess which cannot be avoided in a reactor or neutron environment, they are severely limited in their application possibilities. In particular makes this background due to X-ray and gamma radiation such detectors for the individual detection of neutrons or the detection very low neutron intensities unsuitable, so that such detector systems can only detect distributions of intensive event rates depending on location.

It is an object of the invention to provide a detector for electrically neutral particles, in particular Neutrons, indicating which has a high detection sensitivity with a structurally simple and therefore inexpensive structure. It is also an object of the invention to provide a converter device for such a device Detector for the detection of neutral particles and a corresponding manufacturing process to specify the converter device. After all, it's a job of the invention, a corresponding method for detecting electrically neutral Propose particles.

The respective tasks are performed by a detector according to claim 1 Converter device according to claim 11, a method for producing a Converter device according to claim 13 and a detection method according to Claim 14 solved. Preferred embodiments of the invention are the subject of the dependent claims.

• ein zumindest bereichsweise mit einem Zählgas gefülltes Detektorgehäuse,
• zumindest eine in dem Gehäuse angeordnete Konvertereinrichtung, welche Konvertierungsprodukte aufgrund einer Absorption der zu detektierenden neutralen Teilchen generiert, wobei die Konvertierungsprodukte elektrisch geladene Teilchen in dem Zählgas erzeugen,
• zumindest eine Ausleseeinrichtung zum Nachweis der elektrisch geladenen Teilchen,
• zumindest eine Driftfelderzeugungseinrichtung zum Erzeugen eines derartigen elektrischen Driftfeldes für die elektrisch geladenen Teilchen in zumindest einem Volumenbereich des Zählgases, so daß die elektrisch geladenen Teilchen zumindest teilweise zu der Ausleseeinrichtung driften,

wobei die Konvertereinrichtung ladungstransparent ausgelegt und derartig in dem Detektorgehäuse angeordnet ist, daß sie von dem Driftfeld zumindest teilweise durchsetzt ist.According to the invention, a detector for detecting electrically neutral particles, in particular neutrons, comprises

• a detector housing filled at least in some areas with a counting gas,
• at least one converter device arranged in the housing which generates conversion products on the basis of absorption of the neutral particles to be detected, the conversion products generating electrically charged particles in the counting gas,
• at least one reading device for detecting the electrically charged particles,
• at least one drift field generating device for generating such an electrical drift field for the electrically charged particles in at least one volume area of the counting gas, so that the electrically charged particles drift at least partially to the readout device,

wherein the converter device is designed to be transparent to charge and is arranged in the detector housing such that it is at least partially penetrated by the drift field.

The detector according to the invention is for the detection of electrically neutral particles, especially neutrons and other neutral particles, in particular Designed photons. The principle of detection is based on the fact that the neutral particles interact with a converter device, which due to this Interaction (for example a nuclear reaction) generates conversion products. For this purpose, the converter device preferably contains a solid converter material. The conversion products subsequently ionize the counting gas or the gas with which the detector housing is at least partially filled and which at least partially surrounds the converter device. hereby electrically charged particles, in particular electrons, are generated, which in the counting gas are movable under the influence of an electric field. To the To be able to detect electrically charged particles, they are under the influence an electrical drift field fed to a readout device. This points the detector has a drift field generating device which, in particular, is separate be provided by the converter device and the readout device can. However, it is equally possible to use the drift field generating device as To design part of the converter device. Also the readout facility can be included to generate the drift field, so that the drift field generating device in particular through a special configuration of the converter and readout device can be realized. According to the invention at least one converter device designed to be charge-transparent, i.e. she owns a high transmission coefficient for the electrically charged particles. Preferably, the electrically charged particles can be retained pass or enforce their location information the converter device.

According to a preferred embodiment, the converter device has a A large number of passages, preferably arranged in a matrix, for the electrical charged particles. The passages can be, for example, as geometric formed openings or holes in the converter device his. Furthermore, a passage can also be made through a transparent charge Zone are formed, which is a compared to the adjacent material has only a small interaction cross-section for the electrically charged particles, so as to have a high transmission coefficient for the charged particles. The converter device particularly preferably has a regular one Matrix of circular breakthroughs.

According to a further preferred embodiment, the passages have a Minimum diameter between 10 microns to 1000 microns, preferably 25 microns to 500 microns and a minimum distance from each other from 10 microns to 500 microns, preferably 15 µm to 300 µm.

According to a particularly preferred embodiment, the detector has a Variety, preferably 2 to 20, most preferably 10, of (in a row) cascaded converter devices. In particular, the Converter devices are spaced from each other, stack-like in the detector housing be arranged so that between the converter devices the counting gas is. This creates a large effective area for the interaction necessary for the detection of the neutral particles the converter device. Due to the transparency of the charge of the converter devices can load the ones generated by the conversion products Particles whose detection enables the detection of the neutral particles by the cascade of the converter devices by means of the drift field to the readout device be moved. The use of cascaded converter devices in the detector according to the invention accordingly enables enormous increase in the available interaction area for the electrical neutral particles and thus a considerable increase in detection sensitivity.

Preferably, one is more active for converting the electrically neutral particles Area of the converter device designed in a planar manner - in particular planar and preferably arranged substantially vertically in the drift field. This A flat or layer-like structure of the converter device enables a further one Improvement of the surface to volume ratio of the converter device. This is because, typically, the (solid) converter material as a whole Volume is sensitive to the neutral particles to be detected However, conversion products often only have a relatively short range have in the converter material and can therefore only emerge from it, if they are sufficiently close to the surface, it is for achieving a high detection sensitivity advantageous for a given converter volume or the largest possible converter area for detection To have available. A particularly efficient and quick derivation of the generated charged electrical particles to the readout device then succeeds when the converter device is arranged substantially vertically in the drift field is. Accordingly, the average field direction of the Drift field essentially parallel to the surface normal of the area trained converter device. Also an inclined arrangement of the converter device is possible as long as the level of the flat converter device is not parallel to the drift field.

According to a preferred embodiment, the drift field generating device a flat, optionally structured drift electrode to the To generate drift field between the drift electrode and the readout device. For the detection of electrons in the counting gas by the conversion products generated, the drift electrode with respect to the readout device negatively biased. The drift electrode can be omitted if whose function is taken over by an electrode layer of the converter device becomes.

According to a particularly preferred embodiment, the converter device comprises a first and a second conductive layer, which is defined by an intermediate one arranged insulator layer are electrically insulated from each other, and at least one preferably arranged on the first and / or second conductive layer Converter layer. The converter device thus has a layer structure on. A plastic film, for example, is used as the insulator layer Polyimide film for use. So-called Kapton films have proven particularly useful (Kapton is a trademark of DUPONT). Through this insulating layer the two conductive layers are electrically insulated from one another. The conductive layers are preferably metal layers, which is applied directly to the insulating layer by a coating process were. In particular, copper layers come in for the conductive layers Consideration. The layered converter device further comprises one Converter layer, which preferably facing away from the insulator layer Surface of the first and / or second conductive layer is arranged. equally However, the converter layer can also be between one of the in particular thin and structured conductive layers and the insulator layer arranged his. If the converter layer can be designed as a conductive layer, can dispense with an additional conductive layer of the converter device become.

Such a particularly preferred layer-like converter device can are produced using so-called GEM foils (gas electron multiplier foils), as for example in US-A-6 011 265 and in the publication of F. Sauli in Nucl. Inst. And Methods A 386 (1997) pages 531 to 543 are. With these GEM films described in the specified publications are Kapton foils coated on both sides with copper, which 1997 were developed by F. Sauli at CERN. Using a photolithographic The process involves etching a regular hole structure into these GEM foils The copper top and bottom of the foils are not electrically connected to one another are. On the detailed disclosure regarding the manufacture, the construction as well as the electrical wiring and other properties of the GEM films is fully directed to the disclosure of the present invention References cited above, so that the disclosure these publications form an integral part of the disclosure of the present invention should be. For a complete repetition of those in these publications detailed description of the GEM foils can thus be dispensed with.

The layered converter device described differs however, in particular compared to the GEM foils proposed by F. Sauli due to the additional converter layer. Furthermore, the GEM foils in the applications discussed in the cited publications only operated in a gas boost mode. There are one suitable electrical wiring such field strengths between the two conductive layers built up that there is an avalanche-like multiplication of the Primary electrons comes so that the foils a "gas electron multiplier" (GEM) represent. Preferably, the converter devices according to the present However, inventions are not operated in such a gas amplification mode, it only becomes the charge-transparent property of the GEM films exploited.

According to a further preferred embodiment, the first and second conductive layer of the converter device via a converter field generating device electrically connected to each other. The converter field generating device enables the generation of an electrical drift field, which in particular in addition to the drift field generated by the drift field generating device can work. This ensures that the electrically charged particles can be efficiently guided through the converter device.

The (fixed) converter layer preferably contains a neutron converter layer, so that the detector is suitable for the detection of neutrons, the Neutron converter layer in particular lithium-6, boron-10, gadolinium-155, gadolinium-157 and / or uranium-235 contains. Should be UV and / or as neutral particles X-ray photons are detected, especially Csl as a material for the photon converter layer.

According to a further preferred embodiment, the converter layer a layer thickness of 0.1 microns to 10 microns, preferably for a substantially neutron converter layer consisting of boron-10 between 0.5 µm to 3 µm, most preferably about 1 µm, the first and second conductive layers one Layer thickness of 0.1 microns to 20 microns, preferably 0.2 microns to 10 microns and the insulator layer a layer thickness of 10 μm to 500 μm, preferably 25 μm to 100 µm.

According to the invention comprises a converter device for a detector for Detection of electrically neutral particles, especially neutrons, a first and second conductive layer, which is arranged between an insulator layer are electrically insulated from one another, and at least one is preferred the (fixed) converter layer arranged in the first and / or second conductive layer, the converter device being arranged in a plurality of preferably matrix-like Has passages for electrically charged particles. Such Converter layer can be used in conjunction with a conventional gas detector simple and highly sensitive detection of neutral particles, in particular Neutrons. For this purpose, the converter device in the Drift field of the gas detector introduced. Not one is particularly preferred single converter device, but a "stack" of cascaded converter devices used, which makes the detection sensitivity enormous can increase.

The converter device preferably contains a neutron converter material, so that the converter device for a detector for the detection of neutrons is designed, the neutron converter material in particular lithium-6, boron-10, Gadolinium-155, Gadoliniuim-157 and / or Uranium-235 contains.

• Vorsehen einer zwischen zwei elektrisch leitfähigen Schichten angeordneten Isolatorschicht, so daß die elektrisch leitfähigen Schichten gegeneinander elektrisch isoliert sind; und
• Vorsehen einer Konverterschicht, insbesondere einer Neutronenkonverterschicht.

According to the invention, a method for producing a converter device for a detector for detecting electrically neutral particles, in particular neutrons, comprises the steps:

• Providing an insulator layer arranged between two electrically conductive layers, so that the electrically conductive layers are electrically insulated from one another; and
• Providing a converter layer, in particular a neutron converter layer.

The neutron converter layer preferably contains at least one above called neutron converter material. As described above, the invention Converter device in particular from a so-called GEM film are produced, to which an additional converter layer is applied becomes. For example, on a GEM film using electron beam evaporation of a boron-10 powder or granulate, a boron-10 layer is evaporated become.

• Auffangen der zu detektierenden elektrisch neutralen Teilchen mit zumindest einer Konvertereinrichtung, welche bei Absorption der neutralen Teilchen Konvertierungsprodukte generiert;
• Erzeugen von elektrisch geladenen Teilchen in einem Zählgas bzw. Gas durch die Konvertierungsprodukte;
• Ableiten bzw. Beschleunigen der elektrisch geladenen Teilchen in einem elektrischen Driftfeld zu einer Ausleseeinrichtung, wobei die elektrisch geladenen Teilchen zumindest teilweise durch die ladungstransparente Konvertereinrichtung hindurchgeleitet werden, insbesondere durch eine Vielzahl vorzugsweise matrixartig angeordneter Durchgänge in der Konvertereinrichtung; und
• Nachweisen der elektrisch geladenen Teilchen in der Ausleseeinrichtung.

According to the invention, a detection method for the detection of electrically neutral particles, in particular neutrons, comprises the steps:

• Collecting the electrically neutral particles to be detected with at least one converter device which generates conversion products when the neutral particles are absorbed;
• Generating the electrically charged particles in a counting gas by the conversion products;
• Deriving or accelerating the electrically charged particles in an electrical drift field to a readout device, the electrically charged particles being at least partially passed through the charge-transparent converter device, in particular through a plurality of passages arranged preferably in a matrix in the converter device; and
• Detection of the electrically charged particles in the reading device.

The charge-transparent design of the converter device allows the charged particles without losing their location information through the Conversion facility (s) can be directed. Hence it follows from the Charge transparency that the place of production of the charged particles in the Counting gas undistorted by the converter device (s) to the preferably location-sensitive readout device is mapped or directed.

Figur 1

eine schematische Schnittansicht eines Detektors zum Nachweis von Neutronen gemäß einer Ausführungsform der Erfindung;

Figur 2a

eine schematische, perspektivische Ansicht eines Detektors zum Nachweis von Neutronen gemäß einer weiteren Ausführungsform der Erfindung;

Figur 2b

eine schematische, perspektivische Ansicht des in Figur 2a gezeigten Detektors, jedoch mit einer unterschiedlichen Ausleseeinrichtung;

Figur 2c

eine schematische, perspektivische Ansicht des in Figur 2a gezeigten Detektors, jedoch mit einer weiteren unterschiedlichen Ausleseeinrichtung;

Figur 2d

eine schematische, perspektivische Ansicht des in Figur 2a gezeigten Detektors, jedoch mit einer weiteren unterschiedlichen Ausleseeinrichtung;

Figur 3

eine schematische Schnittansicht durch eine Konvertereinrichtung, wobei Feldlinien des lokalen elektrischen Feldes schematisch gezeigt sind; und

Figur 4

eine schematische Schnittansicht samt perpektivischer Detailansicht einer Ausführungsform einer Trageinrichtung für Konvertereinrichtungen.

The invention is described below by way of example with reference to the accompanying drawings. It shows:

Figure 1

is a schematic sectional view of a detector for detecting neutrons according to an embodiment of the invention;

Figure 2a

is a schematic, perspective view of a detector for detecting neutrons according to another embodiment of the invention;

Figure 2b

a schematic, perspective view of the detector shown in Figure 2a, but with a different reading device;

Figure 2c

a schematic, perspective view of the detector shown in Figure 2a, but with another different readout device;

Figure 2d

a schematic, perspective view of the detector shown in Figure 2a, but with another different readout device;

Figure 3

a schematic sectional view through a converter device, field lines of the local electric field are shown schematically; and

Figure 4

is a schematic sectional view including perspective detailed view of an embodiment of a support device for converter devices.

Figure 1 shows a highly schematic sectional view and Figure 2 schematic perspective views of a detector for the detection of neutrons according an embodiment of the invention. First, using Figures 1 and 2 the structure of the detector is described.

In a detector housing 10, which can be part of a conventional gas detector, a (not shown) gas or counting gas is introduced via a gas supply 12. A gas discharge 14 is also provided for venting the detector housing. All counting gases common for gas detectors can be used. It is only necessary that the conversion products formed in the nuclear reaction to be described later have an ionizing effect on the gas. Mixtures of argon with one or more of the components CO ₂ (10-90% content), CF ₄ , dimethyl ether, isobutane and CH _{4 have} proven to be particularly suitable. In contrast to conventional helium-3 neutron detectors, it is not necessary for the counting gas to be kept under high pressure, but can advantageously be introduced into the detector housing 10 under normal pressure.

An entry window 16 is embedded in the top of the detector housing 10. Since the detector shown is preferably not with an increased counting gas pressure is operated, the entrance window 16 can be made very thin, so that it only a small cross section for the absorption of the incident neutrons having. In addition, the incident neutrons become very insignificant distracted by the thin entrance window. In the detector housing 10 is adjacent at or near the entrance window 16 a drift electrode 18 arranged, which is part of a drift field generating device. Between the Drift electrode 18 and a readout device 19 to be described later an electrical drift field for electrical via a voltage source (not shown) charged particles are applied, the drift electrode with respect to the Readout device 19 is subjected to a negative voltage. At the Drift electrode 18 can optionally be a layer 20 of a solid neutron converter, for example, a boron-10 layer.

In the embodiments of the invention shown in Figures 1 and 2 Detector, the drift field generating device comprises the drift electrode 18 first Electrode and the readout device as a (structured) second electrode. It is however also possible instead of using the readout device 19 as the second electrode to provide a separate second drift electrode. Further The function of the drift electrode 18 can also be determined by a conductive layer adjacent converter device 22 are taken over, so that on the Drift electrode 18 can be dispensed with.

In the detector housing 10 there are also three cascaded one above the other Converter devices 22 are provided. The converter devices 22 are located essentially in that between the drift electrode 18 and the readout device 19 generated drift field. As shown in particular in Figure 3, are the converter devices 22 are preferably constructed and exist in layers For example, from a so-called GEM film (see above), which on one or both sides with a fixed converter layer 24 - here a neutron converter layer Boron-10 - is coated. Preferably, the converter layer 24 is essentially applied homogeneously, but the converter layer 24 only in some areas or can be applied in different layer thicknesses. Each of the converter devices 22 comprises an insulator layer 26, for example a polyimide film. Kapton films have proven particularly successful (Kapton is a trademark of DUPONT company). The insulator layer 26 is conductive on both sides Material, such as copper, coated, so that they between a first conductive layer 28 and a second conductive layer 30 is arranged. The Both electrically conductive layers 28 and 30 are through the insulator layer 26 electrically isolated from each other. Furthermore, the converter device 22 has a A plurality of passages 32 arranged in a matrix, through which passages electrically can drift charged particles in a manner to be described. The Arrangement patterns of these passages 32, which the converter devices 22 Enforcing in the normal direction of the layer plane is shown schematically in FIG. 2 shown.

The construction, the electrical wiring and the manufacture of the GEM foils, from which preferred converter devices according to the invention are produced in a simple manner 22 is detailed in US-A-6,011,265 as well as in the publication by F. Sauli, "GEM: A new concept for electron amplification in gas detectors ", Nuclear Instruments and Methods in Physics Research A 386 (1997), pages 531-534. To repeat all of them to avoid aspects and properties of GEM foils described there, is fully disclosed below on the disclosure of these References referred to. Thus, the description of the Construction, the electrical wiring and the production of the GEM films in the mentioned publications an integral part of the disclosure of this invention The GEM foils described in the specified publications (gas electron multiplier films) are essentially double-sided Copper-coated Kapton foils, developed by F. Sauli at CERN in 1997 were. By means of a photolithographic process, these GEM foils are a regular hole structure is etched, with copper top and bottom of the foils are not electrically connected.

Opposite the entrance window 16 and the drift electrode 18 in the detector housing 10 the readout device 19 is arranged such that the cascaded Converter devices 22 are arranged in a stack-like manner therebetween. The Surface normals of the entrance window 16, the drift electrode 18, the converter devices 22 and the readout device 19 preferably essentially fall together. The mean field direction of the electrical drift field between neighboring ones Converter devices 22 is substantially perpendicular to the Layer planes of the converter devices 22 so that they are the longitudinal axis of the hole-like passages 32 follows. The drift electrode 18 and the readout device 19 are spaced from the converter devices 22, with the intermediate space is filled by the counting gas.

All conventional detector systems can be used as readout device 19 with which charged particles, in particular electrons, can be detected are. For example, the readout device 19 is comb-like or interdigital interlocking electrode structures can be used, which are schematic are shown in Figure 2a and Figure 2b. However, they are also multi-wire gas chambers or similar detectors can be used. To prove the captured charged particles - here electrons - is conventionally used with a (not shown) detection electronics a voltage signal between the two interdigital electrodes evaluated.

In addition to comb-like and interdigital readout structures (see FIGS. 2a and 2b), which only provide the location information in one dimension are the same read out structures crossed to one another, which have a spatial resolution in deliver two dimensions of space. A reading device 19 "modified in this way is shown schematically in Figure 2c. Here are two crossed each other Readout structures arranged on the top and bottom of a carrier plate. As well are interesting - especially for scattering experiments - ring-shaped readout structures, because these integrate over the entire azimuth angle and the entire intensity deliver for a scattering angle. Such a reading device 19 "'with an annular Readout structure is shown in Figure 2d.

Figure 4 (a) is a schematic sectional view of a preferred support 36, with which a large number of converter devices arranged in cascade 22 can be attached in the detector housing 10. The carrying device 36 has four, for example, mounting brackets made of a ceramic material 38 on which are fixed to a base plate 40. At each of the Mounting brackets 38 is a corner portion of a substantially rectangular one designed clamping frame 42 attached.

As shown in the exploded perspective view of Figure 4 (b), points the tensioning frame 42 has an upper 44 and a lower 46 frame element. The Frame elements 44 and 46 consist of a conductive material, for example Stainless steel. One of the converter devices is located between the frame elements 44, 46 22 kept under such a mechanical tensile stress, that it is set essentially smooth and without drapes. Between respective Layer sides of the converter device 22 and the frame elements 44 and 46 U-shaped insulating elements 48, for example Kapton foils, are introduced, which have a direct contact between the frame elements 44, 46 and the enable the respective layer sides of the converter device 22 only in regions. As a result, the converter device can thus be held in the clamping frame 42 be held that the upper frame member 44 with the first conductive Layer 24 and its lower frame element 46 with the second conductive Layer is electrically connected while frame members 44 and 46 are isolated from each other.

The mode of operation of the illustrated embodiments of FIG described detectors according to the invention. The neutrons to be detected are at least partially from the converter layers 24 of the converter devices 22 absorbed. The converter layer 24 consists essentially of isotope-pure Boron-10, which has proven to be particularly suitable, decays after absorption of the neutron the boron-10 nucleus spontaneously split into an α-particle and an Lithium-7 core. Because the momentum of the absorbed neutron is comparatively is small and therefore negligible, the α-particle and the lithium-7 Flying core apart in opposite directions due to the conservation of momentum. At least one of these conversion products will therefore differ from the layer level of the converter device 22 or from the converter layer 24 move away and ionize the counting gas. In this way, in particular, free Electrons generated in the counting gas.

Such ionization traces of the conversion products are shown schematically in FIG shown. Make the primary electrons generated by this process the signal actually to be detected. The charge cloud of the primary Electrons are released from the electrical drift field, which is between the drift electrode 18 and the reading device 19 is applied, in the direction of the reading device 19 deducted. At least some of the electrons generated must one or more of the converters 22 pass to the Readout device 19 to arrive. This is made possible by the transparency of the charge the converter devices 22, which allow the primary electrons, to get to the reading device 19 without losing their location information, so that by means of a spatially resolved detection of these electrons the reading device 19 also on the ionization site of the counting gas - and thus the absorption site of the neutron to be detected - can be closed.

As detailed in US-A-6-011 265 and the above publication by F. Sauli, GEM foils have suitable electrical wiring charge-transparent properties. So lace up, as schematically is shown in Figure 3, the electric field lines of the drift field in the range Passages 32 of converter devices 22 together when one is drifting supporting potential difference between the first conductive layer 28 and the second conductive layer 30 is applied. In the field direction behind the Passages 32 of the converter devices 22 widen the electric field lines symmetrically again. A primary electron, which is characterized by the ionizing Effect of a conversion product in which count gas was generated follows this Course of one of the field lines shown in Figure 3 and can thus through the passage 32 upon receipt of its location information by one or more converter devices 22 are "smuggled".

In contrast to the mode of operation of the GEM films, as they are mentioned Publications is described, the potential difference between the first conductive layer 28 and the second conductive layer 30, which over a Converter field generating device are electrically connected to each other, preferably chosen small. So it is not necessary in the area of the passageways 32 to build up such field strengths in the converter devices 22, which too would lead to a gas amplification of the primary electrons because of the conversion products of each individual neutron sufficient primary electrons for one direct evidence can be generated. Consequently, the converter devices 22 not like GEM films as a gas amplifier with amplification factors between 10 and 100 wired, but work without amplification (amplification = 1). Because of the total energy available for the conversion products reinforcement is therefore not necessary or only to a small extent, so that a very high operational stability and lifespan of the detector is achieved becomes.

The described structure of the embodiments of the detector according to the invention for neutrons advantageously allows the use of a fixed neutron converter. Solid neutron converters of this type, for example converter layers from boron-10, are much better for one for basic reasons efficient detection of neutrons because of the density of the converter atoms in a solid neutron converter about 1000 times larger than in gaseous ones Is a converter and thus a significantly higher cross section for neutrons having. In conventional neutron detectors, the use of fixed leads However, converter materials lead to detection problems of the loaded conversion products. To a large extent, these remain in the converter material themselves stuck and can only limit their energy to a surrounding one Dispense the detection medium (e.g. a counting gas). Can be demonstrated effectively conversion products originating only from surface layers. The advantage of a tightly packed neutron absorber in the form of a solid is therefore due to the lack of conventional neutron detectors again Probability of the loaded fragments to escape into the surrounding detection medium destroyed.

Since the fixed neutron converter and the counting gas are decoupled from each other, the counting gas can be used under normal pressure, so that no pressure vessel necessary is. Operation at normal pressure in turn enables construction detectors of any size and with various shapes.

The use of neutron detectors has proven to be particularly advantageous, which comprise converter devices 22 arranged in cascade. So this makes it possible to have a particularly favorable ratio of the surface area of a To provide converter layer to its converter volume. The usage fixed neutron converter regularly draws problems with the Proof of the loaded conversion products themselves. These conversion products to a large extent already remain in the fixed converter themselves stuck and can only transfer their energy to a surrounding area to a small extent Detection medium, e.g. deliver a counting gas. Be detected can effectively only convert products originating from surface layers. Thus, the advantage of a densely packed neutron absorber may be possible in the form of a solid due to the low probability of leakage the conversion products in the surrounding detection medium destroyed become.

The charge-transparent design of the converter devices according to the invention 22, however, preferably allows multiple converter devices 22 cascaded one after the other for duplication or improvement of the Use detection efficiency. The actual ionization signal, i.e. the educated primary electrons, the converter devices can due to the charge transparency 22 penetrate while receiving their location information so that the entire electron signal is used to detect the absorbed neutrons can be. When using boron-10 as converter material in the converter layers 24 of a detector according to the invention, which 10 on both sides comprises coated, cascaded converter devices 22, is obtained For example, a detection efficiency of 75% for 2 meV neutrons, 50% for 25 meV neutrons, 35% for 100 meV neutrons and about 25% for 200 meV neutrons. These high detection efficiencies of the detector system according to the invention are comparable to those of high-pressure helium-3 gas detectors.

The primary charge in the cascade of charge-transparent converter devices 22 can be generated - as described - from any electrode array be demonstrated as the execution of the readout device 19. The type and shape of the read-out device 19 result in a simple manner the spatial resolution. From the shape and duration of typical charge pulses there is a typical acceptance rate of about 10 million neutrons per second and pixel. The size of a pixel and thus the spatial resolution is due to the range of the loaded conversion products limited to about 2 mm x 2 mm at normal counting rates under normal pressure. Thus, the inventive detector concept presented here has an approx Rate acceptance 1000 times greater per pixel and 10 times better linear Spatial resolution than previous helium-3 gas detectors for neutrons on.

Another advantage of the invention lies in the fact that in the invention Detector for the use of materials with a high atomic number can be dispensed with. This results in an inherent insensitivity to Gamma and X-rays. When using, for example, Bor-10 as the active one Converter material, the signals can also because of the shape of the pulse height spectrum without problems against the remaining X-ray and Discriminate gamma background. The detector according to the invention is in its Embodiment as a neutron detector consequently for gamma and X-rays insensitive.

The converter devices 22 can in particular be made in a simple manner from conventional ones GEM films are made in one or preferably both Surfaces of the GEM film are provided with converter layers 24. As special has been suitable for the production of such converter devices 22 electron beam evaporation of powdery or granular and isotopically pure Boron-10 proved. The boron-10 layer has a layer thickness of approximately 3 μm an optimum for the ratio of the neutron absorption probability and the escape probability of the loaded conversion products the fixed convector into the counting gas, since the maximum range of the charged Conversion products in Bor-10 is only about 3.5 µm.

LIST OF REFERENCE NUMBERS

10

detector housing

12

Zählgaszufuhr

14

Zählgasabfuhr

16

entrance window

18

drift electrode

19

reading device

19 '

reading device

19 "

reading device

19 " '

reading device

20

Layer of a neutron converter on the drift electrode

22

converter devices

24

converter layer

26

insulator layer

28

first conductive layer

30

second conductive layer

32

crossings

34

field lines

36

support means

38

mounting brackets

40

baseplate

42

tenter

44

upper frame element

46

lower frame element

48

insulating

Claims (14)

Detector for the detection of electrically neutral particles, in particular neutrons, with a detector housing (10) at least partially filled with a counting gas, at least one converter device (22) arranged in the detector housing (10) which generates conversion products due to absorption of the neutral particles to be detected, the conversion products generating electrically charged particles in the counting gas, at least one readout device (19) for detecting the electrically charged particles, at least one drift field generating device (18) for generating such an electrical drift field for the electrically charged particles in at least one volume range of the counting gas that the electrically charged particles drift at least partially to the readout device (19), wherein the converter device (22) is designed to be charge-transparent and is arranged in the detector housing (10) such that it is at least partially penetrated by the drift field. The detector of claim 1, wherein the converter means (22) is a plurality of passages (32), preferably arranged in a matrix, for the electrically charged particles. The detector of claim 2, wherein the passages (32) have a minimum diameter between 10 µm to 1000 µm, preferably 25 µm to 500 µm and a minimum distance of 10 µm to 500 µm, preferably 50 µm to 300 µm. A detector according to any one of the preceding claims, wherein the detector a plurality, preferably 2 to 20, most preferably 10, cascading arranged converter means (22). Detector according to one of the preceding claims, wherein one for the Conversion of the active area of the converter device (22) area-like designed and preferably arranged substantially vertically in the drift field is. Detector according to one of the preceding claims, wherein the drift field generating device (18) a flat, possibly structured Drift electrode (18) to the drift field between the drift electrode (18) and the readout device (19). Detector according to one of the preceding claims, wherein the converter device (22) first (28) and second (30) conductive layers which by means of an insulator layer (26) arranged between them are electrically insulated, and at least one preferably on the first (28) and / or second (30) conductive layer arranged converter layer (24) includes. The detector of claim 7, wherein the first (28) and second (30) conductive Layer electrically connected to a converter field generating device are. The detector of claim 7 or 8, wherein the converter layer (24) is a neutron converter layer which is in particular lithium-6, boron-10, gadolinium-155, Contains Gadolinium-157 and / or Uranium-235. The detector of claims 7 to 9, wherein the converter layer (24) is a Layer thickness of 0.1 microns to 10 microns, preferably for a substantially Neutron converter layer consisting of boron-10 between 0.5 µm to 3 µm, most preferably about 1 µm, the first and second conductive layers a layer thickness of 0.1 µm to 20 µm, preferably 0.2 µm to 10 µm and the insulator layer has a layer thickness of 10 μm to 500 μm, preferably Has 25 microns to 100 microns. Converter device (22) for a detector for the detection of electrically neutral Particles, especially neutrons, with a first (28) and a second (30) conductive layer through an interposed insulator layer (26) are electrically insulated from one another, and at least one preferably arranged on the first (28) and / or second (30) conductive layer fixed converter layer (24), the converter device (22) being a A plurality of passages (32), preferably arranged in a matrix, for has electrically charged particles. A converter device according to claim 11, wherein the converter device (22) a neutron converter material, in particular lithium-6, boron-10, gadolinium-155, Contains Gadolinium-157 and / or Uranium-235. Method for producing a converter device (22) for a detector. for the detection of electrically neutral particles, in particular neutrons, with the steps: Providing an insulator layer (26) arranged between two electrically conductive layers (28, 30) so that the electrically conductive layers (28, 30) are electrically insulated from one another and Providing a converter layer (24), in particular a neutron converter layer. Detection method for the detection of electrically neutral particles, in particular neutrons, with the steps: Collecting the electrically neutral particles to be detected with at least one converter device (22), which generates conversion products when the neutral particles are absorbed; Generating electrically charged particles in a counting gas by the conversion products; Deriving the electrically charged particles in an electrical drift field to a readout device (19), the electrically charged particles being at least partially passed through the charge-transparent converter device (22), in particular through a plurality of passages (32) in the converter device (22), preferably arranged in a matrix. ; and Detection of the electrically charged particles in the readout device (19).

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