The object of the invention relates to a detector wire array arrangement for two-dimensional nuclear wire detectors, which detector wire array arrangement has a first and second detector wire array containing spanned detector wires spaced from each other, each detector wire has an axis, the first detector wires of the first detector wire array determine a four-sided first enveloping surface delimited by first and second sides parallel to each other and by third and fourth sides connecting the end points of these, and the sides of which intersect the axis of each first detector wire at a total of two points outside of the wire, and which is the smallest-perimeter four-sided shape with such characteristics; the second detector wires of the second detector wire array form a four-sided enveloping surface delimited by fifth and sixth sides parallel to each other and by seventh and eighth sides connecting the end points of these, and the sides of which intersect the axis of each second detector wire at a total of two points outside of the wire, and which is the smallest-perimeter four-sided shape with such characteristics.

The object of the invention also relates to a two-dimensional nuclear wire detector containing the detector wire array arrangement according to the invention.

Some two-dimensional position-sensitive nuclear detectors contain a network of thin wires. In case of such detectors most often the network of wires is placed in a sealed, typically rectangular chamber in such a way that these cover the detection surface located between the two parallel sides of the rectangular shape with the largest area. In such a case the covering is realised so that two rectangular wire planes are provided preferably at a small distance from each other parallel to each other and provided separately per dimension to ensure the primary signals of the two-dimensional position-sensitive detection. Providing these typically takes place according to an arrangement illustrated in Figures 1 a and 1 b, where Figure 1 a depicts a top view of a detector wire array arrangement 1 10 of a wire detector according to the state of the art, while Figure 1 b depicts a perspective exploded view of the detector wire arrays according to Figure 1 a, in which the two detection wire planes of the detector wire array arrangement 1 10 can be seen, in each of which a wire array 1 10a, 1 10b is tensioned on a frame 120a, 120b. Parallel, i.e. not intersecting, wire filaments 1 1 1 a and 1 1 1 b are tensioned densely between the opposing sides of the rectangular first and second wire arrays 1 10a, 1 10b. The wire filaments 1 1 1 a, 1 1 1 b are perpendicular to the given side of the rectangle at their starting and ending points, and the axis planes of the wire filaments 1 1 1 a, 1 1 1 b located in the two wire arrays 1 10a, 1 10b are also perpendicular to each other. As a consequence of this arrangement the electronic signals that may be separately obtained from the two wire arrays 1 10a, 1 10b can be processed individually per lines, i.e. as a coordinate in a planar Cartesian coordinate system and the two data together provide a planar position.

Typically, further wire planes (wire arrays) are used in order to implement nuclear detecting, which is illustrated schematically in the wire detector 101 shown in Figure 2. The additional drift wire array 500 and anode wire array 502 are not required in order to detect position; instead these are used for producing the electric signals of impact and for ensuring the appropriate signal strength. The detector wire array arrangement 1 10 presented above is arranged in a detector chamber 102, which has a suitable ionisable active gas volume 600 between the anode wire array 502 and the drift wire array 500. When the charged nuclear particles 104 enter the wire detector 101 on the side opposite the detector back wall 103, it is the molecules or atoms of this gas volume 600 that are ionised, i.e. large numbers of the electrons surrounding them are split off due to the impact of the charged nuclear particles 104 to be detected. In certain cases, such as in the case of detecting neutrons, it is the nucleus of the gas in the gas volume 600 that enters into a nuclear reaction with the incoming neutron, and as a result one or two high-speed, characteristically approx. 0.8 MeV charged particles are produced, which create the aforementioned ionisation in the same way. A constant high voltage between the drift wire array 500 and the anode wire array 502, for example -3,000 V direct voltage connected to the drift wire array 500 and +3,000 V direct voltage connected to the anode wire array 502, the drift wire array 500 and the anode wire array 502 ensure that a static electric voltage field is provided between them, due to which the electrons split off during ionisation start to accelerate and move in a direction perpendicular to these arrays. As a consequence of the accelerated electrons and their cascade effect, a substantial electric signal is created in the detector wire arrays 1 10a, 1 10b at the geometrical position where the original ionisation took place. Although a single ionisation position is usually spread out and so a signal is actually caused in several detector wire filaments 1 1 1 a, 1 1 1 b at the same time, the electronic processing of these will ensure that the geometrical position of the average centre point is determined by determining the geometrical centre of the signals.

Theoretically it is possible to construct wire detectors wherein it is possible to determine the position of impact from the electric signals coming from each wire filament of the detector wire planes by detecting the signal per wire and along the length of the wire. In such a case a single detector wire plane would be sufficient for detecting. In practice, especially when detecting neutrons, simultaneous signal reading performed in parallel and simultaneously for each wire filament in addition to determining signal propagation in the direction along the wire using one method or another, even with very fine time resolution, or by using the charge division method, in order to determine position cannot be effectively technically implemented, as such a multi-channel solution is unnecessarily costly and is not even sufficiently reliable. This is why the use of two detector array planes is preferred.

Therefore the customary arrangement is a rectangular or square shaped planar detector wherein the wires are spanned between the opposite sides at a distance of a few mm from each other. The most common is an arrangement consisting of four wire planes where the first electron accelerating wire plane is at a negative direct potential of several thousand volts, the third is an anode wire plane at a positive direct potential of several thousand volts, where a significant proportion of the electrons finally impact, and the second and fourth wire planes are at earth potential, and it is from the wires of these two latter wire planes that the useful position signals are obtained. The reading of the signals may take place using one of several types of methods: either by reading the signal of every wire filament simultaneously and by adding the obtained signal strengths as a weighted, e.g. digitally calculated sum, or with the neighbouring wires connected by a T-type electronic filter arranged artificial L-C-L or R-C-R delay line and by measuring the delay time of the signals, or with the neighbouring wires connected through a resistor element to form an artificial chain of serial resistors and by using the charge division measurement method at the two ends of the series to determine the position in one dimension.

The density of the wire filaments in a given direction, i.e. the distance of the parallel wire filaments from each other, must be selected so that the electric charge signal created can be detected on several, characteristically 3 to 7 filaments, whereby the weighted sum of the voltage signals makes it possible to determine the position as precisely as possible. Therefore the position distribution is a result of the scale of the distance between the filaments, such as half of the filament distance. In this way the distribution of position can be characterised by the area of a square with sides equal in length to half of the distance between the filaments, where the centre of the square indicates the position of impact.

For reasons of design, practicality and economy the filaments mentioned above as neighbouring filaments do not represent single wire filaments, instead these parallel filaments are handled electrically in pairs, i.e. the two neighbouring filaments are treated as one.

Due to this everywhere in the specification where a single filament is mentioned, this may actually be a single wire filament, but it may also be two wire filaments parallel to each other, i.e. a pair of filaments, which are electrically connected to each other where they are fixed. Similarly, optionally, more than two parallel wire filaments may be electrically grouped, but in practice the grouping of more than 4 wire filaments using such reading methods is not typical.

In the conventional arrangement containing four wire planes, although the direction of the wires of the first and third wire planes is of no importance, and any array can be used, the wire filaments of the third and fourth wire planes are perpendicular to each other for the determination of position, and as a result of this both opposing side pairs of the rectangular or square shaped detector are connected to each other.

In practice, detector systems are also conventionally implemented where the two-dimensional detecting surface is a curved surface. The reason for this is that if the particles of radiation made to pass through a sample are to be measured at the same distance from the sample in various directions, and the significant inverse square reduction of the intensity of radiation over distance is not desired, such as in case of diffraction measurements, then a detector geometry is preferred where the set of the detection points of the detector is located on a spherical surface. This may be a square shaped, rectangular shaped or optionally shaped detector surface that is folded on a spherical surface. If, however, the detector surface is significantly spanned out in one direction, which is frequently the case in practice, this is usually implemented by creating a shape folded onto the surface of a cylindrical shell instead of a sphere for the sake of simplicity, where the longer side of the detector follows the curve of the cylindrical shell. This combined arrangement is called a banana-shaped detector.

However, such a detector surface cannot be realised by merely stretching out wire filaments, because straight filaments cannot be spanned in a curved direction. One of the conventional solutions for this is to use straight detector tubes, which provide much worse position resolution as compared to wire filament arrangements, where the straight tubes stand in the direction of the axis of the cylindrical shell, and the tubes together take on the shape of a curved square or rectangle. The other solution is to stretch straight wires spannedin the non-curved direction, while thin parallel conductors implemented on circuit boards customary in electronics are provided perpendicularly and these circuit boards are positioned in the gas volume of the detector in a curved way for an extended length. The disadvantage of this is that the penetration of the particles to be detected into the solid board and their dispersion there makes this solution difficult to implement and/or disadvantageous.

A general requirement is that the active surface of the detector should be continuous, i.e. in the ideal case there should be no interruption, frame, inactive section or inactive surface part formed anywhere in the detector surface. In other words, in the above case an electronic circuit board should be placed on a curved surface for a length of as much as several metres without any interruption in it, which generally has significant limitations.

In the context of the present invention, both the planar and the curved surfaces are regarded as two-dimensional surfaces. In the context of the present invention a two-dimensional surface is understood to mean any planar or curved surface embedded in a three-dimensional space. From the point of view of nuclear detectors particularly relevant two-dimensional surfaces include squares, rectangles, a section of a cylindrical shell, a section of a spherical shell, but naturally the demand for the use of other surfaces may arise.

In other words a two-dimensional nuclear wire detector is two-dimensional in the sense that the impact of the nuclear particle is detected by being projected onto a two-dimensional planar or curved surface.

The objective of the invention is to provide a wire detector and a two- dimensional detector wire array arrangement with a planar or curved surface, with good position resolution, i.e. operating with spanned wire filaments, the detection surface of which is not close to a square shape, instead it is shaped as an elongated rectangle, or a parallelogram, or any other shape.

As an example, the detector surface may be of an elongated rectangle shape where one of the two opposing pair of sides is much longer than the side length of conventional detectors having a maximum length of 1 metre, and a typical length of 40 cm, while the shorter opposing sides fall within this customary size range. In such a case the wires of the detection wire plane between the shorter opposing sides would have to be spanned inside the gas volume along a length which is too long, corresponding to the length of the longer side of the rectangle, which has mechanical and, therefore, feasibility limitations.

In order to satisfy the other practical demand a curved detector plane needs to be provided with better two-dimensional position resolution than in the case of detector tubes, i.e. with the use of wire filaments.

These objectives are achieved with the detector wire array arrangement according to claim 1 , and with the nuclear wire detector according to claim 7.

Certain preferred embodiments of the invention are defined in the dependent claims.

Further details of the invention will be explained by way of exemplary embodiments with reference to the figures, wherein

Figure 1 a is a top view of a detector wire array arrangement of a wire detector according to the prior art,

Figure 1 b is a perspective exploded view of the detector wire arrays according to Figure 1 a,

Figure 2 is a schematic side cross-sectional view of a two-dimensional nuclear wire detector according to the prior art,

Figure 3 is a schematic top view of a detector wire array arrangement according to the invention,

Figure 3a is a top view of the first detector wire array of the detector wire array arrangement according to Figure 3,

Figure 3b is a top view of the second detector wire array of the detector wire array arrangement according to Figure 3,

Figure 3c is a view illustrating the angles between two wires of the detector wire array arrangement according to Figure 3 and one side of the frame,

Figure 3d is a schematic enlarged view of four crossing wires of the detector wire array arrangement according to Figure 3 in the vicinity of the crossings,

Figure 3e illustrates the determination of the angle between two wires, Figure 4 is a schematic top view of a further detector wire array arrangement according to the invention, where the angle between the axis of the two detector wire arrays is perpendicular,

Figure 5 illustrates a possible way of securing the wires of a further detector wire array arrangement according to the invention where preferably there are no wires secured to the shorter sides, and where the angle between the axis of the detector wire arrays are preferably symmetrical, and acute,

Figure 6 is a schematic top view of the detector wire arrays and an enveloping surface of an irregular-shaped detector wire array arrangement according to the invention,

Figure 6a is a schematic top view of a first wire array and first enveloping surface of the detector wire array arrangement according to Figure 6,

Figure 6b is a schematic top view of a second wire array and second enveloping surface of the detector wire array arrangement according to Figure 6, Figure 7 is an exploded perspective schematic view of two wire arrays with curved surfaces of a two-dimensional detector wire array arrangement according to the invention,

Figure 7a is a top view of the wire arrays according to Figure 7,

Figure 7b is a cross-sectional view of the detector wire array arrangement according to Figure 7 taken along line l-l,

Figure 8 is a schematic circuit diagram illustrating a possible electrical connection of the detector wires, and

Figure 9 depicts an exemplary wire detector according to the invention containing a drift wire array and an anode wire array.

Figure 3 shows a schematic top view of the detector wire arrays 10a, 10b of a detector wire array arrangement 10 according to the invention. The first wire array 10a is shown separately in Figure 3a and the second wire array 10b is shown separately in Figure 3b. As shown, the wires 1 1 of the wire arrays 10a and 10b cross each other in top view, however as the first and second wire arrays 10a, 10b are spaced from each other within the detector wire array arrangement 10, the first wires 1 1 a of the first wire array 10a do not come into contact with the second wires 1 1 b of the second wire array 10b.

Both the first wire array 10a and the second wire array 10b are provided such that the wires 1 1 are spanned in a first frame 20a and a second frame 20b of the wire arrays 10a, 10b, which frames 20a, 20b are rectangular in the present case. The frames 20a and 20b can also be formed as a single element, in such a case the frame 20a is understood to mean the frame part on which the wires 1 1 a of the first wire array 10a are spanned, and the frame 20b is understood to mean the frame part on which the wires 1 1 b of the second wire array 10b are spanned. The first frame 20a of the first wire array 10a has a first side 21 and a second side 22 parallel to each other, and a third side 23 and a fourth side 24 parallel to each other and perpendicular to the first and second sides 21 , 22. The second frame 20b of the second wire array 10b has a fifth side 25 and a sixth side 26 parallel to each other and to the first and second sides 21 and 22, and a seventh side 27 and an eighth side 28 perpendicular to these, and also parallel to each other. The majority of the first wires 1 1 a are spanned between the first side 21 and the second side 22 of the first frame 20a, and in such a way so that they are at an angle a to the first side 21 as depicted in Figure 3c. The rest of the first wires 1 1 a are either spanned between side 21 and side 23, or between side 24 and side 22 of the first frame 20a. The axes of these latter first wires 1 1 a are also at angle a to the side 21 of the first frame 20a. In other words the first wires 1 1 a are all preferably parallel to each other, and in the interest of simplifying positioning preferably each first wire 1 1 a is located at an equal distance from the neighbouring first wires 1 1 a. Consequently, the detector wire array 10a is an array within which the wires 1 1 a do not cross each other. Similarly, the majority of the second wires 1 1 b are spanned between the fifth side 25 and the sixth side 26 of the second frame 20b, and in such a way so that they are at an angle b to the fifth side 25 as illustrated in Figure 3c. The rest of the second wires 1 1 b are either spanned between the fifth side 25 and the eighth side 28, or between the seventh side 27 and sixth side 26 of the second frame 20b. The axes of these latter second wires 1 1 b are also at angle b to the fifth side 25 of the frame 20b. In other words the second wires 1 1 b are all parallel to each other, and in the interest of simplifying positioning preferably each second wire 1 1 b is located at an equal distance from the neighbouring second wires 1 1 b. Consequently, the detector wire array 10b is an array within which the wires 1 1 b do not cross each other.

If 180° - b = a is fulfilled, then the first and second wires 1 1 a, 1 1 b are symmetrically inclined with respect to each other.

The angle g between the first wires 1 1 a and the second wires 1 1 b facing the first side 21 equals the angle (b - a), as is shown in Figure 3d. The angle g between any first wire 1 1 a and second wire 1 1 b facing the first side 21 is understood to mean the following in the context of the present invention. As illustrated in Figure 3e, a plane S is provided at a middle point F of section k connecting points A and B of the given first wire 1 1 a and the second wire 1 1 b closest to each other and which plane S is perpendicular to the section k, and the perpendicular projections 1 1 a’ and 1 1 b’ of the first wire 1 1 a and the second wire 1 1 b, as well as the perpendicular projection 2T of the first side 21 are generated on this plane S. The angle g is the angle between the perpendicular projection 1 1 a’ of the first wire 1 1 a and the perpendicular projection 1 1 b’ of the second wire 1 1 b that faces the perpendicular projection 2T of the first side 21 . Naturally, the perpendicular projections of the sides 22, 25 or 27 could have been used as well, however this has no special significance in the present case, the definition was only presented in the interest of the comprehensibility of the angle between the straight lines running in different planes.

The detector wire array arrangement 10 according to the invention differs from the solution according to the state of the art in that none of the wires 1 1 a or the wires 1 1 b is parallel to any side 21 , 22, 23, 24, 25, 26, 27, 28, and the same pair of sides of the first and second frame is used to span a portion of the wires 1 1 a, 1 1 b, while no wires 1 1 a, 1 1 b are spanned between the other pair of sides (sides 23 and 24, and sides 27 and 28) on either of the two frames 20a, 20b. This wire arrangement has several advantages.

In the arrangement according to the invention, the wires may even be at an angle of 90 degrees with respect to each other, for example in such a way that the wire directions are separately at 45 degrees and 135 degrees to the first side 21 , and to the fifth side 25, as it may be observed in Figure 4. If the ratio of the sides of the rectangular shaped frames 20a, 20b exceeds the value of the square root of two, then the wire lengths according to the invention are certain to be all less than the individual maximum wire length necessary in a conventional parallel, perpendicular wire arrangement, because there the length of the longer wires is the same as the length of the larger side. With the present arrangement, no wire length exceeds the length of the shorter side of the frame 20a, 20b multiplied by square root of two (V2) in the case of the detector wire array arrangement according to the invention containing wires 1 1 a, 1 1 b perpendicular to each other and spanned in an elongated rectangular shaped frame 20a, 20b. As opposed to the conventional solution of stretching the wires between the opposing sides of the frame, where a problem may occur if an overly long wire has to be spanned between a pair of sides, in the case of the present invention the longer sides (in the present case sides 21 , 22, 25, 26) of the frames 20a, 20b of the detector wire array arrangement 10 may be of any length, because there are no wires 1 1 spanned parallel with these between the shorter sides (sides 23, 24, 27, 28).

In the case of the embodiment shown in Figure 4, one of the pairs of sides of the rectangular shaped frames 20a and 20b is significantly longer than the other pair. This does not cause any problem in the case of the wire arrangement according to the invention as there are no wires 1 1 that are spanned between the shorter pair of sides, therefore the length of the longer pair of sides may be practically of any size. Due to the difference in length of the first and second wires spanned between the shorter pair of side and longer pair of sides in the case of conventional wire assemblies, the longer wires must be spanned significantly more in order to prevent the wires from becoming slack, which represents a great mechanical load on the shorter sides. These problems maybe overcome with the inclined wire arrangement according to the present invention.

If the angle between the wire directions of the detector wire arrays 10a, 10b is not 90 degrees, but a different angle, then this may result in further preferred detector characteristics. For example, if the wire array 10a, 10b has an elongated rectangular shape and the angle between the first and second wires 1 1 a, 1 1 b is less than 90 degrees and if the arrangement is symmetrical, i.e. the angles to the side are 45+x degrees and 135-x degrees, then the length of the wires 1 1 a, 1 1 b may be shorter than the square root of two multiplied by the length of the shorter sides. In this way it is possible to construct the detector wire array arrangement 10 according to the invention with shorter wire lengths, resulting in only a slight reduction in the position resolution in one direction.

It should be noted that a reduction in one direction in the position resolution is not always unfavourable. For example, it may be the case that the size of the detector has to be increased in one geometrical direction so that a large number of nuclear particles are collected in order to obtain better statistics, but in this direction position is not overly significant, because all that is done is that the number of impacting particles is summed, while in the other direction, however, the measurement of the position of the impact gives the effective sense of the measurement, here fine position resolution is very significant.

It is preferred to avoid too large values of x and to approach 45 degrees, otherwise the wire directions of the wire arrays 10a, 10b become close to parallel with each other, while substantial shortening of the length of the wires 1 1 a, 1 1 b is no longer achieved.

From the point of view of the angles a and b the advantage of symmetrically inclined wires 1 1 a and 1 1 b is that even in the case of rectangular shaped wire arrays 10a, 10b the length of the wires 1 1 a connecting the first side 21 and the second side 22 equals the length of the wires 1 1 b connecting the fifth side 25 and the sixth side 26. This facilitates implementation.

Figure 5 shows a detector wire array arrangement in the case of which no detector wires 1 1 a, 1 1 b are attached to the shorter sides 23, 24, 27, 28 of the rectangular frames 20a, 20b. The broken line K shows the rectangular inner area where two-dimensional position determination is possible.

If the wires 1 1 are only spanned between the pairs of the longer sides (sides 21 , 22, 25, 26) parallel to each other of the frames 20a, 20b and no 1 1 wires are attached to the shorter sides 23, 24, 27, 28, then the area covered by the wires 1 1 of both inclination directions will not be precisely rectangular, therefore a precisely rectangular shaped detector surface cannot be obtained. However, in the case of a significantly elongated rectangular shaped detector wire array arrangement 10 it may be preferred if no mechanical securing of wires 1 1 or electrical contact is provided on the other, shorter pairs of sides (sides 23, 24, 27, 28). If the longer sides 21 , 22, 25, 26 are selected to be sufficiently large, then, a precisely rectangular shaped clear detector surface of a suitable size is obtained if the non-rectangular portions extending beyond it are disregarded. These non-rectangular portions can be sufficiently reduced if the angle g between the wire directions of the two wire arrays 10a, 10b is not 90 degrees, but smaller than this (in other words an acute angle), and if the inclination of the wires 1 1 a, 1 1 b is symmetrical.

It should be noted here that although in the case of the embodiments shown the distance measured between the neighbouring wires 1 1 a, 1 1 b is the same in both wire arrays 10a, 10b, however, this is not an absolutely necessary condition. The distance between the wires 1 1 may be different within the two wire arrays 10a, 10b. The distance between the wires 1 1 may even vary within the same wire array 10a, 10b if higher resolution measurements are required in certain locations.

Before a discussion of the further advantages of the wire arrangement according to the invention, the concept of enveloping surfaces will be introduced. It is apparent that the wire arrangement according to Figure 3, for example, can be realised not only with the use of rectangular shaped frames 20a, 20b. Even in the case of arbitrarily shaped frames 20a’, 20b’ as illustrated in Figures 6, 6a and 6b the same wire arrangement can be achieved within the frames 20a’, 20b’ as within the frames 20a, 20b according to Figure 3, as illustrated in Figure 6 by the exemplary frames 20a’, 20b’ that would fit within the rectangular shaped frames 20a, 20b of Figure 3. If the wires 1 1 are to be secured on the frames 20a’, 20b’, then the length of the first wires 1 1 a is selected to be the same as the length of their portion within the first frame 20a’, and their ends are secured at the points where they meet the first frame 20a’. Similarly, the length of the second wires 1 1 b is selected to be the same as the length of their portion within the second frame 20b’, and their ends are secured at the points where they meet the second frame 20b’.

The wire arrangement within these arbitrarily shaped frames 20a’, 20b’ can be more easily described with the help of enveloping surfaces 30a, 30b illustrated in Figures 6, 6a and 6b.

The detector wires 1 1 a of the first detector wire array 10a spanned on the frame 20a' depicted in Figure 6a are located within a four-sided first enveloping surface 30a that is delimited by the parallel first side 31 and second side 32, and by the third side 33 and fourth side 34 connecting the end points of the first side 31 and the second side 32. In such a case the first detector wire array 10a contains first detector wires 1 1 a the axes t1 of which intersect the first side 31 and the second side 32, or the first side 31 and the third side 33, or the second side 32 and the fourth side 34.

The detector wires 1 1 b of the second detector wire arrays 10b spanned on the frame 20b' illustrated in Figure 6b are located within a four-sided second enveloping surface 30b that is delimited by the parallel fifth side 35 and the sixth side 36, and by the seventh side 37 and the eighth side 38 connecting the end points of the fifth side 35 and the sixth side 36. In this case the second detector wire array 10b contains second detector wires 1 1 b, the axes t2 of which intersect the fifth side 35 and the sixth side 36, or the fifth side 35 and the eighth side 38, or the seventh side 37 and the sixth side 36.

Naturally, many enveloping four-sided shapes are conceivable that satisfy the requirements described above, for example another rectangle containing the enveloping surface 30a or the enveloping surface 30b. In the context of the present invention the term enveloping surface 30a, 30brefers to the two-dimensional shape with the smallest perimeter which is delimited by four sides and contains the axis t1 or t2 of every wire 1 1 a, 1 1 b, respectively, of the given wire array 10a, 10b, and the sides of which intersect the axis t1 or t2 of every wire 1 1 a, 1 1 b, respectively, at a total of two points outside of the wires 1 1 a, 1 1 b. As a limit these two points may be understood to include the end points of the wires 1 1 a and 1 1 b.

The enveloping surfaces 30a, 30b of the detector wire array assemblies 10 according to the invention also fulfil the condition that the two enveloping surfaces 30a, 30b have another pair of sides that are parallel to each other (sides 31 and 32, and sides 35 and 36) which intersect at least some of the wires 1 1 a, 1 1 b, or their axes t1 and t2. In the case of the wire detectors 101 according to the state of the art this condition is not fulfilled, because there the smallest perimeter enveloping surfaces are the surfaces determined by the frames 120a, 120b, but the pairs of sides of the frames connected by the wires 1 10a, 1 10b are not parallel, instead, typically, they are perpendicular to each other, as it can be seen in Figures 1 a and 1 b.

The aforementioned advantages can also be achieved with the wire arrangement according to the invention if the frames 20a’, 20b’ shown in Figure 6 or other planar non-rectangular frames 20a’, 20b’ are used, similarly to the case when the previously shown rectangular frames 20a, 20b are used. This can be easily understood from the fact that a rectangular (or, as a special case, square) enveloping surface 30a, 30b can be drawn around every planar frame 20a’, 20b’. Again, the advantage is, contrary to the conventional solution, that in case of the detector wire array arrangement 10 according to the invention the pairs of sides (sides 31 and 32, and side 35 and 36) of the enveloping surfaces 30a, 30b which are connected by the axis t1 or t2 of the detector wire 1 1 a, 1 1 b, respectively, are also parallel to each other, while the pairs of sides (sides 33 and 34, and sides 37 and 38) lying in the transversal direction are not connected by any axis t1 or t2.

The definition of the enveloping surfaces 30a, 30b is not limited to the case of irregular frames 20a’, 20b’, enveloping surfaces 30a, 30b can be provided in case of the previously shown rectangular wire arrays 10a, 10b as well, which substantially coincides with the rectangle determined by the frames 20a, 20b as will be appreciated. The use of the word "substantially" refers to the fact that in contrast to the theoretical definition of the enveloping surface 30a, 30b, the frames 20a, 20b have a finite thickness, and the detector wires 1 1 a, 1 1 b terminate somewhere there within.

The enveloping surface 30a, 30b are not only suitable for characterising wire arrays 10a, 10b which are spanned on planar frames 20a, 20b. As stated above, in practice there is often the need for curved detector surfaces, such as cylindrical shell shaped detector surfaces, the construction of which raises the problems detailed above.

Flowever, the wire arrangement according to the invention makes it possible to create a detector surface in a simple way that has a substantially cylindrical shape. This is illustrated in Figures 7, 7a, and 7b.

In the case of the embodiment according to Figure 7, an exploded schematic view of a partial cross-section of the central section of a detector wire array arrangement 10 following the shape of a cylindrical shell can be seen, in addition to which an exemplary detector back wall 13 has also been shown in the interest of illustration. The frames 20a, 20b of the two wire arrays 10a, 10b of the detector wire array arrangement 10, and the detector back wall 13 each follow the shape of concentric cylindrical shells 40a, 40b and 43, as it may be observed in top view in Figure 7a.

In Figure 7 only the sides 21 , 22, 25, 26 of the frames 20a, 20b running perpendicular to the generators on the cylindrical shell surfaces have been shown. Only a small number of the first and second detector wires 1 1 a, 1 1 b have been shown from the wires 1 1 , which are spanned diagonally between the sides 21 , 22, 25, 26, as illustrated in the Figure 7, the inclination of the wires 1 1 a, 1 1 b being symmetrical to each other. As it can be observed surfaces Fa and Fb determined by the wires 1 1 a and 1 1 b of the wire array 10a and the wire array 10b, respectively, are not only curved along the cylindrical surfaces 40a and 40b, but are also curved along their generators, in other words in the vertical direction in Figure 7. This is a consequence of the fact that the wires 1 1 a connecting the circular section shaped sides 21 , 22 depart from the plane of the given cylindrical shell 40a, 40b, respectively, as it can be best observed in Figure 7a. Figure 7b shows a cross- sectional view of the wire arrays 10a, 10b and of the detector back wall 13 taken along the direction I - I according to Figure 7. It can also be observed in this cross- section view that the first wires 1 1 a and the second wires 1 1 b do not fall onto a generator of the cylindrical shell 40a, or 40b, instead they define two curved arcs.

It can be seen that if one end point of, for example, the first wire 1 1 a is at a given distance f according to the spatial rules of distance measurement from the curved rectangular plane of the surface of the back wall (see Figure 7a), then although the other end point of the given wire 1 1 a is at the same distance f, the middle of the wire 1 1 a will be more distant from this plane, as a consequence of the inclined orientation. In this way the curved surface Fa is not the same shape as the surface Fd of the curved detector back wall 13. Flowever, the two detector wire arrays 10a, 10b preferably contain wires 1 1 a, 1 1 b with inclination symmetrical to each other, due to this, from the point of view of practical application, they are displaced with respect to each other in a geometrical sense. The reason for this is that in practical applications the radius of curvature of the detector surfaces Fa, Fb of the wire arrays 10a, 10b is typically greater than the distance between the projection of the two end points of the wire 1 1 a or 1 1 b on the plane perpendicular to the surfaces Fa, Fb (in other words the length of the wires 1 1 a, 1 1 b viewed in top view in Figure 7a). In this case the projections of the wires 1 1 a, 1 1 b in Figure 7a are, in practice, the displaced versions of each other, which results in the distances of the wire arrays 10a, 10b (or the curved enveloping surfaces 30a, 30b containing them) being substantially constant at every point.

If the detector surface of the wire arrays 10a, 10b is significantly elongated (in other words the length of the sides 21 , 22, 25, 26 significantly exceeds the distance of the sides 21 and 22, and the sides 25 and 26), then the significant effects of the curved structure only appear along the direction of the elongated sides, and the effect of the curve along the direction of the generators of the cylindrical shells 40a, 40b is negligible from the point of view of detection.

As it can be seen, with the wire arrangement according to the invention the wire arrays 10a and 10b can be produced with an elongated, curved detector surface and containing wires 1 1 a, 1 1 b by spanning the wires 1 1 a, and 1 1 b between the curved sides 21 and 22, and the curved sides 25 and 27, respectively, preferably symmetrically inclined with respect to each other, while the sides 23 and 24, and the sides 27 and 28 are not connected by wires 1 1 a and 1 1 b, respectively.

In the case of the preferred embodiment shown in Figure 7c there is no wire 1 1 a secured on the sides 23 and 24 linking the sides 21 and 22 of the frame 20a, and similarly there is no wire 1 1 b secured on the sides 27 and 28 linking the sides 25 and 26 of the frame 20b either. In this way the shape of the sides 23, 24, 27, 28 is irrelevant from the point of view of detection, preferably the sides 23, 24 linking the sides 21 and 22, and the sides 27, 28 linking the sides 25 and 26, are parallel to the generators of the cylindrical shell 40a, and parallel to the generators of the cylindrical shell 40b, in other words the frames 20a, 20b are preferably shaped as a curved rectangle.

In this case the sides 31 , 32, 35, 36 of the enveloping surfaces 30a, 30b run along the sides 21 , 22, 25, 26 of the frames 20a, 20b, while the sides 33, 34, 37, 38 of the enveloping surfaces 30a, 30b run along each of the two outer wires 1 1 a and 1 1 b due to the requirement of minimal perimeter. In such a case the axes t1 and t2 of the wires 1 1 a, 1 1 b only intersect the sides 31 , 32, 35, 36. Naturally it is also conceivable that the outer wires 1 1 a, 1 1 b are secured along the side 23, 24 and 27, 28 of the frames 20a, 20b, respectively, as illustrated in Figure 7d. In this case the shape of the sides 23, 24, 27, 28 is preferably the curved shape shown in Figure 6a, so that the distance of the detector surfaces Fa, Fb does not change at the edges of the wire arrays 10a, 10b either. In this case the perimeter of the enveloping surfaces 30a, 30b coincides with the perimeter of the frames 20a, 20b, respectively.

The frames 20a, 20b on which the wire arrays 10a, 10b are spanned may define two-dimensional curved surfaces that differ from a cylindrical shell surface, the sides 21 , 22, 25, 26 parallel to each other may run along any convex curved line. Similarly, the parallel sides 31 , 32, 35, 36 of the enveloping surfaces 30a, 30b may correspond to any curved line, such as a parabolic line or elliptical section.

A wire arrangement is illustrated in Figure 8 in the case of which the detector wires 1 1 spanned on the frame 20 are formed as a bundle containing two wire filaments 12, and the ends of the wire filaments 12 within the individual bundles are at a common potential (for example they are connected to each other with a cable having negligible resistance), due to this in the course of signal processing during the detection the wire 1 1 formed as a bundle can be treated as if it were a single wire filament 12. Optionally, the wires 1 1 formed as a bundle may contain more than two detector wire filaments 12, and it is also conceivable that there are more wire filaments 12 in certain bundles, and fewer in bundles at other locations.

In the case of the embodiment illustrated in Figure 8 the neighbouring wires 1 1 are connected to an L-C-L delay line with T-type electronic filter arrangement, but the signals of the wires 1 1 may be read out by using any other known method.

In the case of the embodiments detailed above, the wires 1 1 a, 1 1 b may also be bundled wire filaments 12, but they may also consist of a single wire filament 12.

An exemplary embodiment of a wire detector 1 according to the invention is illustrated in Figure 9. Similarly to conventional detectors, the wire detector 1 according to the invention may also contain a drift wire array 50 (see Figure 9) arranged in front of the detector back wall 13 that is spaced from the first and second detector wire array 10a, 10b. The first and second detector wire array 10a, 10b are connected to the same direct voltage (preferably 0 V), and the drift wire array 50 is connected to negative direct voltage as compared to the first and second detector wire arrays 10a, 10b, such as to a direct voltage between -2,500 and -3,500 V.

The wire detector 1 also preferably contains at least one anode wire array 52 spaced from the drift wire array 50, which is preferably arranged between the first and second wire arrays 10a, 10b, as it can be seen in Figure 9. The anode wire array 52 is connected to a positive voltage as compared to the first and second detector wire arrays 10a, 10b, such as to a direct voltage of between +2,500 and +3,500 V. The absolute value of the drift wire array voltage and the anode wire array voltage may be the same or even different.

Naturally other array orders or array assemblies are conceivable within the wire detector 1 , as is obvious for a person skilled in the art. For example, an embodiment may be implemented in the case of which the anode wire array 52 is arranged outside of the detector wire arrays 10a, 10b, even on the same side of the wire arrays 10a, 10b as the drift wire array 50, or on the opposite side. Furthermore, several drift wire arrays 50 and several anode wire arrays 52 may be used as well.

An active gas volume 60 containing ionisable gas is formed in the customary way at least between the drift wire array 50 and the anode wire array 52 within a detector chamber 2 of the wire detector 1. In the case of a preferred embodiment the gas filling the active gas volume 60 is chosen such that the wire detector 1 is suitable for detecting neutrons among nuclear particles.

The drift wire array 50 and the anode wire array 52 may also be formed in the customary way, with the use of wires 1 1 .

In the case of a detector wire array arrangement with a curved detector surface it is practical not only to form the detector wire arrays 10a, 10b with the inventive wire arrangement, but also to provide the wires 1 1 of all other arrays, such as the drift wire array 50 or the anode wire array 52 substantially parallel to either the first detector wires 1 1 a or the second detector wires 1 1 b, i.e. inclined at substantially the same angle so that their distance to the surface Fa, Fb of the wire arrays 10a, 10b is constant. This is particularly preferred in case that the anode wire array 52 is arranged between the detector wire arrays 10a, 10b.

Various modifications to the above disclosed embodiments will be apparent to a person skilled in the art without departing from the scope of protection determined by the attached claims.