RU2139778C1 - Method for manufacture of output window of gas electroluminescent detector of ionizing radiation - Google Patents

Abstract

FIELD: diffusion welding, applicable in production of ionizing radiation monitors. SUBSTANCE: the method consists in moulding of a translucent disk, annular metal cup, application of a grid electrode in the form of thin-filmed parallel or intersecting conducting tracks onto one of the plane end faces of the disk by the method of vacuum deposition, and sealed joining of the translucent disk to the cup by means of diffusion welding through a plastic metal wire interlayer, registering the centers of the circles, whose diameters are selected from the proposed relation; diffusion welding is accomplished through a plastic metal interlayer in the form of two concentric wire rings located between the translucent disk and cup, orienting the disk with the electrode towards the cup. EFFECT: enhanced reliability of gas electroluminescent detector. 2 dwg

Description

 The invention relates to the field of diffusion welding of glass-metal assemblies and can be used in x-ray and nuclear instrument engineering, in particular, in the technology of manufacturing detectors where ionizing radiation is recorded due to light radiation from a working gas, for example, electroluminescent detectors, gas proportional scintillation counters, etc. d.

A gas electroluminescent detector in general is a gas-filled metal-ceramic case, one of the ends of which has an input window made of beryllium foil, a focusing system made inside the case and two grid electrodes forming a scintillation zone between them, and an X-ray absorption zone in the space before the entrance window of quanta, and an exit window fixed to the second end of the housing, representing glass translucently connected to a metal ring cuff th disk, made depending on the specific conditions of materials such as uviole glass, quartz, magnesium fluoride MgF ₂ . The output window is one of the main components of the detector, because through it the final information signal in the form of a light stream is received and recorded by a photoelectronic multiplier, and the level of technology for its manufacture, in particular the one-piece connection of glass with a cuff, largely determines the technical parameters of the detector as a whole.

 A known method of manufacturing the output window of a gas scintillation proportional counter [1], in which an adhesive connection is provided for the glass disk from the material "suprasil" with elements of a ceramic-metal casing.

 The main drawback in this case is that the use of adhesive joints limits the permissible detector degassing temperatures, leads to contamination of the working gas with adhesive components and, ultimately, sharply reduces the detector’s working life and necessitates the connection of a rather complex gas purification system.

A known method of manufacturing the output window of a gas electroluminescent ionizing radiation detector [2], comprising shaping a metal ring cuff and a translucent disk from a single crystal of magnesium fluoride MgF ₂ , which has several advantages compared to other glasses, for example, quartz. About 90% of the electroluminescence of xenon, most suitable as the working gas of the detector, passes through a window of MgF ₂ . The light guide disk of MgF ₂ is hermetically connected to the metal cuff using high-temperature enamel.

In this case, the disadvantages of the previous method — the analogue associated with the use of adhesives — are eliminated, which improves the purity of the working gas of the detector. However, a significant drawback of the above technology is that the high-temperature enamel used to connect the MgF ₂ disk and the cuff is a dielectric. This prevents the implementation of such an effective (from the point of view of the detector’s functioning as a whole) technical solution, such as the formation of a second grid electrode by vacuum metallization in the form of thin-film parallel or intersecting paths directly on the flat surface of the MgF ₂ light guide disk facing the inside of the detector. The fact is that, in general, the implementation in the internal volume of the detector, as indicated above, of two grid electrodes causes the formation of two functional zones: the absorption zone between the input window and the first grid electrode and the scintillation zone between the first grid electrodes. However, along with this, a third, non-working zone is formed - between the second grid electrode and the exit window. This non-working gas gap leads to additional losses of the light flux and uneven illumination of the output window, i.e. there is an incomplete collection of the light flux and distortion of the final information signal of the detector.

 The solution to this problem could be the formation of the metal structure of the second grid electrode directly on a flat surface of the translucent disk facing the detector. However, this is possible if the technology for manufacturing the output window provides for the closure of the ends of all thin-film tracks of the grid electrode by some switching element, which makes it possible to supply an electric potential to this electrode through a metal cuff. It is obvious that neither high-temperature enamel, nor glue in the first analogue method can in principle fulfill the function of a switching element, since they are dielectrics. Another option for supplying the electric potential to the electrode through thin wire conductors connected to the ends of the thin-film paths, as is used in microelectronics in some cases, is practically impossible in this case. Thus, the disadvantages of this analogous method of manufacturing the input window of a gas electroluminescent detector are limited technical capabilities and relatively low operating parameters of the detector.

Based on the foregoing, and by the greatest number of common essential features, a method for manufacturing optical elements [3] was adopted as a prototype, which in devices such as gas electroluminescent detectors are the output windows, which are glass-metal assemblies. The method consists in forming a translucent disk with an outer diameter D _d and an annular metal cuff, the inner diameter D _{p of} which determines the working diameter of the output window. A thin-film metal coating with a thickness of about 0.1 μm is applied by vacuum deposition to one of the flat end surfaces of a translucent disk by diffusion welding of a disk with a cuff through an annular metal layer with a thickness of about 200 μm. The sprayed coating, which in general can act as an electrode, is used in this technology as an element that activates the welding process and improves the conditions for the formation of a diffusion compound. It is obvious that the welding technology and type of coating are uniquely selected based on the requirements of the welding process. It can be assumed that the coating thickness of approximately 0.1 μm determines its excessively high ohmic resistance, unacceptable for the electrode, and the requirements for the configuration of the grid electrode (for example, the width of each of the tracks within (0.1... 0.15) mm at the distance between the tracks is approximately 1 mm) cause difficulties in subsequent diffusion welding along the stepped glass surface.

The disadvantage in this case is that it is practically very difficult to coordinate and provide a joint solution to three main tasks:
1) the formation of a high-quality metal structure of a thin-film electrode, providing the required electrical properties, a given configuration and the necessary adhesion to the disk material;
2) reliable electrical contact of the thin-film paths of the electrode with the material of the deformed intermediate layer providing stable switching of the electric potential;
3) a vacuum tight, strong connection of a translucent disk with a metal cuff, which determines the reliability of the output window during operation.

 For each of the listed technology elements, there are conditions and criteria for the selection of materials and process parameters, which may have a mutual inconsistency.

 For example, the operation of diffusion welding requires a significant degree of deformation of the intermediate layer, the material of which flows along the joined surfaces, which is accompanied by the appearance of large shear stresses. These voltages can lead to destruction and delamination of the thin-film electrode tracks from the disk. Reducing this deformation to preserve the integrity of the tracks, provided reliable electrical contact is obtained, may not ensure the tightness and the required strength of the connection, and the choice of material and geometry of the electrode based on the conditions of the welding operation will not allow to obtain the necessary functional characteristics of the electrode.

 Thus, the disadvantages of the prototype method are its limited technological capabilities and low reliability of the detector with the output window made according to the described technology.

 The aim of the present invention is to expand technological capabilities and increase the reliability of a gas electroluminescent detector.

где α_∂, α_пр(1) и α_пр(2) - коэффициенты термического расширения материалов светопрозрачного диска и колец прослойки соответственно,
h - конечная толщина деформированной прослойки,
ΔT = (T_св-295)K, T_св - температура сварки,
внутренние диаметры D₁ и D₂ большего и меньшего соответственно колец прослойки определяют из выражений

при этом пластические характеристики и диаметры d₁ и d₂ колец прослойки выбирают исходя из условия
d₂ ≤ d₁, при σ_тт(2)≤ σ_тт(1),
где σ_тт(1) и σ_тт(2) - пределы текучести при температуре сварки материалов большего и меньшего колец прослойки соответственно, а деформирование прослойки при сварке осуществляют до смыкания указанных колец.According to the invention, this goal is achieved by the fact that the grid electrode on the flat surface of the translucent disk is performed by setting the diameter D _{e of the} circle bounding the electrode pattern from the condition D _p <D _e <D _d and ensuring that the centers of the circle of diameters D _e and D _d coincide, intermediate layer is placed in diffusion welding between the translucent plate and a cuff, orienting disc electrode towards the cuff, in the form of two concentric circles of diameters D _e D and _p and another one of larger and smaller rings of wire diameters d ₁ and d _2, respectively, selected from ratios of

where α _∂ , α _{ol (1)} and α _{ol (2)} are the coefficients of thermal expansion of materials of a translucent disk and rings of the interlayer, respectively,
h is the final thickness of the deformed layer,
ΔT = (T _St. -295) K, T _St. - welding temperature,
the inner diameters D ₁ and D _{2 of the} larger and smaller rings of the layer, respectively, are determined from the expressions

while the plastic characteristics and diameters d ₁ and d _{2 of the} rings of the layer are selected based on the condition
d ₂ ≤ d ₁ , for σ _{TT (2)} ≤ σ _{TT (1)} ,
where σ _{tt (1)} and σ _{tt (2)} are the yield strengths at the welding temperature of the materials of the larger and smaller rings of the interlayer, respectively, and the deformation of the interlayer during welding is carried out before the closure of these rings.

The invention is illustrated by the drawing, in which in FIG. 1 shows a diagram of the assembly of parts of the output window before the welding operation, and FIG. 2 is a General view of the welded input window. In the drawing are indicated:
1 - translucent disk of the output window;
2 - an annular metal cuff;
3 - mesh electrode deposited in the form of thin-film conductive tracks on the inner flat end surface of the translucent disk;
4 - a larger outer ring of the initial intermediate layer;
5 - smaller inner ring of the original intermediate layer;
6 - the final configuration of the metal intermediate layer, providing welding of the disk 1 with the cuff 2;
D _p - the working diameter of the output window, determined by the inner diameter of the annular cuff 2;
D _d - the outer diameter of the translucent disk 1;
D _e - the diameter of the circle bounding the pattern of the grid electrode 3;
d ₁ - the diameter of the wire ring 4;
d ₂ - the diameter of the wire ring 5;
D ₁ - the inner diameter of the wire ring 4;
D ₂ - the inner diameter of the wire ring 5;
L ₁ is the final width after welding of the deformed ring 4;
L ₂ is the final width after welding of the deformed ring 5;
h is the final thickness of the intermediate deformed layer 6 after welding;
O'O "- axis of symmetry of the output window, on which lie the centers of the circles of diameters
The essence of the method consists in sequentially performing the following set of technological operations.

Means of machining (turning, milling, stamping, grinding, lapping, polishing) carry out the formation of a translucent disk 1 with plane-parallel ends with an outer diameter of D _d and an annular metal cuff 2 with an inner diameter of D _p . Obviously, the annular cuff 2 may contain, as shown in the drawing, a flat part connected to the disk 1, and a cylindrical one, which is a mounting element for fixing on the reciprocal cuff of the casing (not shown) and subsequent sealing in this place by electronic beam or laser welding. Another option may be the implementation of the cuff 2 in the form of a flat ring with an outer diameter greater than the diameter D _{d of the} disk 1. The specific configuration of the cuff for the invention is not critical.

By any method of vacuum metallization (for example, by thermal evaporation in vacuum), one of the flat end surfaces of the light guide disk 1 is applied using a stencil of the corresponding configuration, a grid electrode 3 in the form of thin film parallel or intersecting conductive tracks, the width, pitch and thickness of which is determined functional characteristics of the electrode and the operating parameters of the detector as a whole. Moreover, the diameter D _{e of the} circle bounding the electrode pattern is chosen to be larger than the diameter D _p and smaller than the diameter D _d , i.e. set from the condition D _p <D _e <D _d , and also ensure the coincidence of the centers of the circles of diameters D _e and D _d , i.e. the placement of these centers on the O'O axis of symmetry. "

Thus, at the point of contact defined by circles with diameters D _p and D _d , along which diffusion welding of the translucent disk 1 and cuff 2 can be carried out, two annular zones are formed:
- the outer zone bounded by circles with diameters D _e and D _d , where there is a clean surface of the translucent disk 1;
- the inner zone bounded by circles with diameters D _p and D _e , on which the ends of the thin-film tracks of the electrode 3.

Next, the formation of two rings of the intermediate layer is carried out:
- a larger ring 4 with an inner diameter D ₁ of wire with a diameter of d ₁ located in the outer end zone of the specified contact (diameters D _e and D _d );
- a smaller ring 5 with an inner diameter D ₂ of a wire with a diameter of D ₂ installed in the inner contact zone of the disk 1 with the cuff 2 (diameters D _p and D _e ).

The assembly before the diffusion welding operation is performed by orienting the disk 1 with the surface on which the electrode 3 is made, towards the joined surface of the cuff 2 and placing the rings 4 and 5 of the interlayer in the indicated outer and inner zones, respectively, while ensuring the concentricity of the rings to one another and to circles with diameters D _e and D _p , or, in other words, setting the location of the centers of circles with diameters D _p , D _e , D _d , D ₁ and D ₂ on the axis of symmetry O'O ".

Next, diffusion welding of the disk 1 with the cuff 2 is carried out, heating the assembly in the appropriate fixture to the required temperature, applying the calculated welding pressure and keeping it for a time sufficient to close the deformable rings 4 and 5 of the interlayer to obtain a thickness h of the final configuration 6 of the interlayer when it total width (L ₁ + L ₂ ).

A similar assembly and welding scheme provides for the initial formation of two autonomous sections:
1) the area of the outer contact zone, where the wire ring 4 provides the flow of welding processes and the implementation of a tight and durable connection; it is obvious that the welding mode and parameters are selected based on the creation of the required conditions for the deformation of the ring 4 in this outer zone;
2) a portion of the inner contact zone, where the wire ring 5 during deformation causes the creation of electrical contact between the ends of all thin-film tracks of the electrode 3 and is a switching element in conjunction with the deformed ring 4 and the sleeve 2, which determine the transfer of electric potential to the electrode 3.

Obviously, for the second section (inner contact zone), the diameter d ₂ and the material of the ring 5 of the interlayer are selected under the actual mode and parameters of the welding process, only on the basis of the conditions for ensuring the necessary electrical contact.

That is, the technology of the joining process as a whole is associated with a variation in the ratio of the diameters d ₁ and d ₂ and the plastic characteristics of the materials of rings 4 and 5, for example, yield strengths at the welding temperature σ _{tt (1)} and σ _{tt (2)} , respectively. With the same material of the interlayer in the case of d ₂ <d ₁ in the inner zone where electrical contact is ensured, there will be a significantly lower degree of deformation of the interlayer compared to the outer zone (welding zone), and therefore lower tangential stresses will occur that do not lead to destruction (peeling, structural disruption, appearance of defects) of thin-film tracks of the electrode 3. Another option is to choose the material of the inner layer 5 with a significantly larger layer than the material of the layer 4 Nost, ie σ _{tt (2)} <σ _{tt (1)} , if, for example, the diameters d ₁ = d _{2 are} equal. In this case, deformation of the interlayer will also be accompanied by significantly lower values of shear stresses. Obviously, the maximum efficiency in this scheme is ensured by the use of both of these factors: both the choice of the difference d ₂ <d ₁ and the provision of the ratio of the plastic characteristics of the materials of the rings 4 and 5 of the interlayer σ _{tt (2)} <σ _{tt (1)} . These options ultimately provide an equivalent final effect associated with the creation in each of these zones of the required conditions for welding and electrical contact. Obviously, under certain conditions, the possibility of realizing both a diffusion connection and electrical contact with d ₁ = d ₂ and σ _{tt (1)} = σ _{tt (2)} , i.e. under conditions of identical thermomechanical influences in each of the corresponding zones. In a generalized form, all of the above options can be expressed by the ratio
d ₂ ≤ d ₁ for σ _{TT (2)} ≤ σ _{TT (1)} .
The closure of the deformed rings 4 and 5 of the interlayer and the formation of the interlayer of the final configuration 6 is advisable, since this allows you to apply electric potential directly to the outer portion of the deformed interlayer, for example, through a wire contact (wire diameter d <h), which extends the technological capabilities of manufacturing the output window if various kinds of design limitations and considerations. It should be borne in mind that with heterogeneous materials of rings 4 and 5 of the interlayer, the welding temperature should not exceed the temperature of formation of a possible eutectic (if the presence of a liquid phase is undesirable).

Essential features of the invention are also such technology elements as the ratio and interdependence of dimensional factors of rings 4 and 5 of the interlayer, disk 1 and cuff 2. Obviously, the diameters d ₁ and d _{2 of} rings 4 and 5 at a welding temperature T _sv will have values
d _{1 (Tsv)} = d ₁ (1 + α _{ol (1)} • ΔT), (1)
d _{2 (Tsv)} = d ₂ (1 + α _{ol (2)} • ΔT), (2)
where α _CR - the coefficient of thermal expansion of the material of the rings of the interlayer;
T = (T _St - 295) K.

Оперируя значениями L_1(Тсв) и L_2(Тсв) и считая, что для L_1(Тсв) возможная максимальная величина (что достаточно наглядно следует из чертежа) составляет
L_1(Тсв)max = 1/2 (D_д - D_э)(Т_св) (7)
и учитывая, что максимально возможный диаметр d₁ через значение L₁ из зависимости (5) выражается в виде

можно с учетом соотношений (7) и (8) записать

что определяет предельно допустимое значение d₁ в соответствии с приведенными выше условиями.And since at T _{sv the} width L _{1 (Tsv)} and L _{2 (Tsv) of} each of the deformed sections (outer and inner) of the interlayer is
L _{1 (Tsv)} = L ₁ (1 + α _d • ΔT), (3)
L _{2 (Tsv)} = L ₂ (1 + α _d • ΔT), (4)
where α _d is the coefficient of thermal expansion of the material of the disk 1, then there are relations:

Using the values of L _{1 (Tsv)} and L _{2 (Tsv)} and assuming that for L _{1 (Tsv) the} maximum possible value (which follows quite clearly from the drawing) is
L _{1 (Tsv) max} = 1/2 (D _d - D _e ) (T _sv ) (7)
and given that the maximum possible diameter d ₁ through the value of L ₁ from dependence (5) is expressed as

taking into account relations (7) and (8), we can write

which determines the maximum permissible value of d ₁ in accordance with the above conditions.

Obviously, the minimum possible value of d ₁ is determined on the basis of welding conditions and takes into account factors such as the degree of deformation, the plasticity of the interlayer, the specific geometry of the disk and cuff, etc., i.e., it is identified individually in each case. It is not possible to designate the minimum allowable value in the form of a mathematical expression due to the large number of different-sized factors that must be taken into account.

При этом достаточно наглядным представляется исходя из конкретных значений при T_св диаметров и величины и диаметра, на котором имеют место смыкания деформируемых колец 4 и 5 прослойки, определить исходные внутренние диаметры D₁ и D₂ колец 4 и 5 прослойки:

Перечисленные технологические операции и математические зависимости определяют совокупность существенных признаков изобретения:
- выбор соотношения D_р < D_э < D_д, с созданием двух зон контакта;
- формообразование прослойки в виде двух концентричных большего и меньшего колец, соответствующих данным зонам;
- взаимная ориентация светопрозрачного диска и манжеты;
- допустимые значения d₁ и d₂;
- величины D₁ и D₂;
- выбор соотношений d₁ и d₂ и пластических характеристик материалов колец прослойки;
- условия деформирования прослойки, которые обеспечивают достижение поставленной цели.By analogy, the maximum possible value of d _{2 is} determined:

In this case, it is quite clear based on specific values at T _{st of} diameters and the magnitude and diameter at which the deformable rings 4 and 5 of the interlayer are closed, to determine the initial internal diameters D ₁ and D _{2 of the} rings 4 and 5 of the interlayer:

The listed technological operations and mathematical dependencies determine the set of essential features of the invention:
- the choice of the ratio D _p <D _e <D _d , with the creation of two contact zones;
- the formation of the layer in the form of two concentric larger and smaller rings corresponding to these zones;
- mutual orientation of the translucent disk and cuff;
- permissible values of d ₁ and d ₂ ;
- values of D ₁ and D ₂ ;
- the choice of the ratios d ₁ and d ₂ and the plastic characteristics of the materials of the rings of the interlayer;
- conditions of deformation of the layer, which ensure the achievement of the goal.

According to the invention, the enterprise has developed design and technological documentation and produced an experimental batch of output windows of a gas electroluminescent detector. The exit windows were a translucent disk of a single crystal of magnesium fluoride MgF ₂ , connected to a cuff of alloy 47 ND, which has the values of thermal expansion coefficients matched with MgF ₂ in the temperature range (295-895) K. The value of D _e was 52 mm, and D _p = 46 mm. Using a magnetron sputtering method, a grid electrode in the form of parallel thin-film chrome tracks 0.15 mm wide with a pitch of 1.5 mm and a coating thickness (1.0 ... 2.0) μm was applied to the inner flat surface of the MdF ₂ disk. The value of D _e was given 49 mm. The intermediate layer was an aluminum wire with a diameter of d ₁ = 0.3 mm for the larger ring and a diameter of d ₂ = 0.2 mm for the smaller ring of the layer. Diffusion welding was performed at T _b = 520 ^o C, pressure (1.5 ... 2.2) kgf / mm ² and a time of 20 min.

In general, this technology made it possible to obtain output windows of a qualitatively new type, which provided a significant improvement in the performance and operating conditions of the gas electroluminescent detector. This consists in the achieved energy resolution (on the MnK line _α E = 5.9 keV) within (8.5. .. 9.0)% compared with the value (9.0 ... 10.0)% in the known samples and increasing the stability of the peak position of the amplitude distribution of pulses from the detector.

 The technical and economic efficiency of the invention consists in a substantial increase in operating parameters and an improvement in the operating conditions of electroluminescent detectors by expanding the technological capabilities of manufacturing their main components, which greatly expands the possibilities for implementing various scientific and technical programs in such fields as X-ray diffraction and X-ray spectral analysis, X-ray astronomy, geology , space technology, nuclear energy, ecology.

Literature
1. G. Manzo, A. Peacock, RDAndzessen, BG Taylor "Preliminary studies of gas filling in scintillation proportional counters 2 IEEE Transactions of Nuclear Science, Vol. NS-27, No.1, February 1980.

 2. Goganov D.A., Schulz A.A., Elkind V.B. "Sealed gas electroluminescent x-ray detector with a focusing system" - Instruments and experimental equipment. 1984, N 2, pp. 206-208.

 3. V. A. Bachin "Diffusion welding of glass and ceramics with metals." -M .: Engineering, 1986, p. 74-87.

Claims (1)

A method for producing output windows gas electroluminescent detector of ionizing radiation, wherein the carried shaping translucent disk diameter D _a, for example, magnesium fluoride single crystal of MgF _2, and an annular metallic collar, the inner diameter D _p which defines the effective diameter of the exit window, is applied by vacuum metallization on one of the flat end surfaces of the disk mesh electrode in the form of thin-film parallel or intersecting conductive tracks and produce tight connection of the translucent disk with the cuff by diffusion welding through a plastic metal wire layer, while combining the centers of the circles of diameters D _a and D _p , characterized in that the grid electrode on the flat surface of the translucent disk is performed by setting the diameter D _{e of the} circle bounding the electrode pattern, conditions of D _p <D _e <D _a and ensuring coincidence of the centers of the circles of diameters D _e and D _a, an intermediate layer with diffusion welding is placed between the translucent plate and ma zhetoy orienting disc electrode towards the cuff, in the form of two concentric circles of diameters D and _E D _p to one another and of larger and smaller rings of wire diameters d ₁ and d _2, respectively, selected from ratios of

where α _a , α _{ol (1)} and α _{ol (2)} are the coefficients of thermal expansion of materials of a translucent disk and rings of the interlayer, respectively;
h is the final thickness of the deformed layer;
T- (T _St. - 295) K, T _St. - welding temperature,
the inner diameters of D ₁ and D ₂ , larger and smaller, respectively, of the rings of the layer are determined from the expressions

while the plastic characteristics and diameters d ₁ and d ₂ rings are selected based on the condition
d ₂ ≤ d ₁ for σ _{TT (2)} ≤ σ _{TT (1)} ,
where σ _{tt (1)} and σ _{tt (2)} are the yield strengths at the welding temperature of the materials of the larger and smaller rings of the interlayer, respectively, and the deformation of the interlayer during welding is carried out before the closure of these rings.

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