WO2014184573A9

WO2014184573A9 - Multi-pixel x-ray detector apparatus

Info

Publication number: WO2014184573A9
Application number: PCT/GB2014/051505
Authority: WO
Inventors: Gary Gibson
Original assignee: Ibex Innovations Ltd
Priority date: 2013-05-16
Filing date: 2014-05-16
Publication date: 2015-01-22
Also published as: WO2014184573A1; GB201308836D0

Abstract

X-ray detection apparatus comprises at least one multi-pixel imaging detector (1) and a structure (2) configured to perturb an x-ray energy spectrum directed at the or each multi-pixel imaging detector (1). The apparatus can be configured to give an output in the form of measurement, an assessment or an image.

Description

Multi-Pixel X-Ray Detector Apparatus

Field of the Invention

The present invention relates to x-ray detectors, and in particular to multi-pixel x-ray detectors.

Background of the Invention

Multi-pixel x-ray imaging cameras are used widely. However, they are relatively expensive pieces of equipment. Further, in comparison with detectors used in cameras configured for detecting visible wavelength spectrum light, they tend to be large, both in terms of individual pixel size and the size of the array.

There is a need for less expensive x-ray detection equipment , even if such equipment is not as accurate as the currently available x-ray imaging cameras. For example, there are a number of applications where an image is not required, but information regarding material type and material thickness is desired. There are also applications where a relatively poor quality of image may be acceptable.

Small area, high resolution imaging detectors are used in various applications such as web cams and mobile phone cameras. These imaging detectors are very cheap, and are capable of detecting x-rays, either directly because they are comprised of silicon and therefore sensitive to x-ray wavelength photons, or with a scintillator to convert x-ray wavelength photons into visible light photons. This class of detector is small in comparison with conventional x-ray detectors. Whereas a small area, high resolution imaging detector typcially has a pixel surface area of under 10 square microns, the individual pixel size in an x-ray detector is in the order of hundreds of square microns. A high resolution multi-pixel imaging detector would typically provide in excess of 1 Mega pixels and have pixel size of 3 micron by 3 micron or less. Such detectors are formed in a 3 mm by 3 mm chip. For example, high resolution multi-pixel imaging cameras having 8 Mega pixels with an individual pixel size of 1.5 micron by 1.5 micron are commercially available. The chip size for such a detector would be 4.5mm by 4.5mm.

Conventional x-ray detectors have comparatively large pixels in order that they may capture as many x-ray photons or visible light photons from a scintillator as possible. Individual pixels would be in excess of 400 microns, with a corresponding chip size of not less than 2cm by 3cm.

However, since high resolution imaging detectors are designed for capturing visible wavelength photons, any detected x-ray signal is likely to be accompanied by a significant amount of noise.

It would be desirable to produce an x-ray detector apparatus in which the detector is a high resolution imaging detector of the type described above.

Summary of the Invention

According to a first aspect of the invention there is provided a multi-pixel x-ray detection apparatus as specified in Claim 1.

According to a second aspect of the invention there is provided a method of analysing at least one material property of an object as specified in Claim 18.

Preferred features of the invention are set out in the claims dependent on Claim 1, in the description and the drawings.

Advantageously, the regions lie laterally of one another, and preferably the structure comprises a plurality of regions lying laterally of one another, and preferably in two orthogonal directions.

Preferably, the member configured to convert incident x-ray wavelength photons into emitted visible wavelength photons is a scintillator. The scintillator may include a scintillator layer and a backing layer.

Advantageously, the plurality of regions is formed in an array, and the array may repeat itself in the structure. For example, the plurality of regions may comprise a three by three array of nine regions, and the structure may include a multiplicity of such arrays.

Preferably, the structure is planar or non-planar. The structure may be curved in at least one plane.

Preferably, the difference between adjacent regions is the thickness of the material of the structure in adjacent regions.

The structure may include a plurality of protrusions or depressions, the thickness of said protrusions or depressions changing in at least one direction thereof, each protrusion or depression providing at least three adjacent regions configured to perturb the x-ray energy spectrum.

Preferably, the protrusions or depressions are pyramidal in shape.

The structure may comprise a non-metallic layer having a multiplicity of depressions formed therein, each depression filled with metal. Preferably, the structure comprises a first non-metallic layer having a multiplicity of depressions formed therein and a second metallic layer including a corresponding number of protrusions each protrusion filling a corresponding depression.

The second layer may cover the surface of the first layer in which the openings to the depressions are situated.

Adjacent depressions or protrusions may be separated from one another by x-ray perturbing material and wherein the material separating adjacent depressions or protrusions may constitute one of the at least three regions.

The non-metallic layer may be formed of silicon. The difference between adjacent regions may be the material from which the individual adjacent regions of the structure are formed.

The adjacent regions may differ in thickness and in the material from which they are made. For example, the structure may comprise a substrate of even thickness, and the individual regions may be formed on a surface thereof by building up discrete layers of material on adjacent regions. The number of layers and/ or the materials of those layers may differ. Techniques such as PVD, electro-deposition or laser ablation may be used to form the individual regions.

In addition, the regional variation may be created by stacking layers of foils with cut-out regions one on top of each other so that the cut out regions stack in such a way to create a variety of thicknesses in a lateral sense.

Another alternative would be to stack a series of wire meshes together in a similar fashion to the foils such that variations in material thicknesses are formed. This is similar to techniques used to form neutral density filters.

Another alternative is to start with a certain thickness of material and cut out regions to create differing thicknesses. This could be done by laser micro-machining or ion-beam milling amongst the many techniques.

Where the material property of the structure, such as thickness of the structure changes continuously rather than by steps, taking any point on the structure, if its property (thickness) is different to the thickness of the structure at an adjacent point, then those two points may each be considered to be regions configured to perturb the x-ray energy spectrum differently.

The said structure configured to perturb the x-ray energy spectrum may be comprised in the scintillator, and may be in either the scintillator layer or a support layer thereof. In some embodiments the x-ray detection apparatus includes or is associated with data recording means where visible wavelength photons are recorded.

In some embodiments the x-ray detection apparatus includes or is associated with a database of recorded information characteristic of known substances.

In some embodiments the x-ray detection apparatus includes or is associated with data processing software, and preferably, such data processing software is configured to perform processing steps to determine a material property of an object or substance.

Where any of the aforementioned data recording means, database, data processor and date processing software are not embodied in the apparatus they may be embodied an another apparatus to which the x-ray detector apparatus of the invention is connected.

It is preferred that in the method of the invention analysis of each pixel is performed on summed signals of a group of pixels, the group of pixels corresponding to the structure or a region of the structure.

The method may comprise the further step of comparing the signals for individual pixels or groups of pixels of the detector with the recorded signals for adjacent pixels or groups of pixels.

The method may comprise the further step of recording the signals for individual pixels or groups of pixels of the detector and comparing the recorded signals with the recorded signals for adjacent pixels or groups of pixels.

The method may comprise the further step of performing the step of recording the signals for individual pixels or groups of pixels of the detector and comparing the recorded signals with the recorded signals for adjacent pixels or groups of pixels without the object present. It is preferred that the method comprises the further step of comparing the current differences between recorded signals between adjacent pixels or groups of pixels.

Preferably, the method comprises the further step of following the step of comparing the signals for individual pixels or groups of pixels with the recorded signals for adjacent pixels or groups of pixels for at least one known material and storing the differences in a database, and comparing the differences between recorded signals for an object under test with the differences between recorded signals in the database.

The method may comprise the further step of producing at least one output representative of the at least one material property.

The method may further comprise the further step of displaying the at least one output on a display means.

Brief Description of the Drawings

In the Drawings, which illustrate preferred embodiments of x-ray detection apparatus according to the invention:

Figure la is schematic representation of a multi-pixel non-imaging x-ray detector;

Figure lb is a schematic representation of an alternative arrangement of non-imaging x-ray detector as shown in Figure la;

Figure 2 is a schematic representation of a x-ray detector comprising an array of multi-pixel x-ray detectors;

Figure 3 is a schematic representation of an x-ray detector of the type illustrated in Figure 2 with an alternative array configuration; Figure 4 is a cross-sectional view of a first embodiment of a scintillator plate;

Figure 5 is a cross-sectional view of a second embodiment of the scintillator plate of Figure 4;

Figure 6 is a rear view of a scintillator plate illustrated in Figure 4 and a front view of the scintillator plate illustrated in Figure 5;

Figure 7 is a cross-sectional view of an interference plate;

Figure 8 is a front view of the multi-regioned structure, i.e. an interference plate illustrated in Figure

7;

Figure 9a is an exploded view of an interference plate built up from a number of layers of material; Figure 9b is a plan view of component parts of an interference plate of the type illustrated in Figure

9a;

Figure 10 is an exploded view of an interference plate built up from a number of layers of wire mesh;

Figure 11 is a schematic representation of an interference plate having a thickness which varies in two directions of the plate;

Figure 12a is schematic, top plan and side views of an alternative embodiment of an interference plate;

Figure 12b illustrates exploded side and schematic views of the embodiment illustrated in Figure 12a; and

Figure 13 is a block diagram illustrating an embodiment of the invention.

Detailed Description of the Preferred Embodiments Figure la illustrates a non-imaging x-ray detector, which comprises a high resolution multi-pixel imaging detector 1 and a multi-absorption plate (MAP) 2. A scintillator may be situated between the MAP 2 and the detector 1, this being illustrated in Figure lb.

Figure lb illustrates a non-imaging x-ray detector, which comprises a multi-pixel imaging detector 1, a MAP 2, a scintillator 5, and an optical coupling 6 between the scintillator 5 and the detector 1. The optical coupling may be a lens or a fibre optic. Where the optical coupling 6 is a lens, the distance between the lens and the detector 1 is the focal length of the lens 6, which focuses light emitted from the scintillator on to the detector 1.

The path between the scintillator 5, optical coupling 6 and detector 1 should be enclosed so that no external light may enter the path, and such an enclosure may extend to the MAP 2. Also, the inner surface of such an enclosure should absorb visible spectrum light, for example it may be painted black. The surface of the MAP 2 facing the detector 1 may have an anti-reflective coating so that stray light does not cause a visible spectrum reflection of the MAP 2 on the detector.

As mentioned above, the detector 1 is not optimised for x-ray imaging and as such the signal from any one individual pixel is likely to be accompanied by significant noise, to the extent that the noise may render the information associated with an individual pixel of little use.

However, by integrating the signals from many of the pixels of the detector 1 into a single measurement, the noise can be removed to such an extent that the measurement is useful. The detector's ability to perform materials identification is enhanced by the MAP 2, which in effect divides the detector 1 into four segments, in the illustrated example. The number of pixels in the detector 1 is such that when divided into four segments, each segment contains a sufficiently large number of pixels to integrate the outputs from individual pixels into a useful measurement. The A/LAP 2 contains four regions 2a— 2d. Each region is materially different to the other, causing a different shift in the energy spectrum of x-ray wavelength photons. Hence, from the detector 1 four different measurements can be produced. With these four different measurements of the same object it is possible mathematically to determine properties of an object 3 when subject to an x-ray energy spectrum emanating from an x-ray source 4.

The detector illustrated in Figure la or lb may be used in the oil industry for determining the proportions of water and oil in a mixture thereof, for example.

Another application would be in the detection of radio active materials. By obtaining a number of different measurements of the same source by virtue of the MAP 2, such a detector may detect not only that a radio active material is present, but also what the radio active material is. Where radio active materials are being detected, the source 4 and object 3 are one and the same, that is the object is also the source of radiation.

An alternative approach is illustrated in Figure 2. Instead of the array of pixels of a detector 1 being divided by a MAP 2, a plurality of multi-pixel detectors 1 form a detector array 10. Each detector 1 is provided with an absorption plate 12a to 12i. Each absorption plate 12a to 12i is uniform, but adjacent absorption plates are different and in the example illustrated in Figure 2, each is absorption plate is different.

Figure 3 illustrates a detector array 10' comprising a 6 x 6 array of detectors 1, each having its own absorption plate, which is uniform, but different to the absorption plate associated with its adjacent detectors 1.

The detector arrays 10, 10' may include a scintillator. Each detector 1 may be associated with its own discrete scintillator. An optical coupling may be provided and the assembly enclosed in the same manner as described in relation to Figure lb. The embodiments illustrated in Figures 2 and 3 have low resolution x-ray imaging capability. The greater the number of detectors the better the x-ray image quality. In fact, the embodiments illustrated in Figures la and lb could be adapted to give low resolution imaging capabilities. This can be achieved by using a multi-absorption plate with a greater number of regions. For example, instead of the two by two array, the array may be six by six, giving thirty six groups of pixels, or ten by ten, giving one hundred groups of pixels.

Alternative multi-absorption plates and scintillator plates are illustrated in Figures 4 to 12b.

Figure 4 illustrates in cross-section a first embodiment of a scintillator plate 13 which comprises a scintillator layer 14 and a support layer 15. The scintillator layer 14 is of a uniform material and has a uniform thickness. Preferably, the material from which the scintillator layer 14 is formed has a strong response to incident x-ray photon energy. However, the support layer 15, comprises a multiplicity of regions of differing thickness represented by numerals 15a to 15d. For the sake of clarity only a sample of regions are numbered.

Figure 5 illustrates in cross-section a second embodiment of a scintillator plate 3 which again comprises a scintillator layer 14 and a support layer 15. The function of the support layer is to protect the scintillator and provide a means of mounting the scintillator to another component in the apparatus.

However, in this embodiment the metal (aluminium) backing layer is of a uniform material and a uniform thickness, whereas the scintillator layer 14 comprises a multiplicity of regions of differing thicknesses represented by the numerals 14a to 14d. For the sake of clarity only a sample of regions are numbered. Preferably, the material from which the scintillator layer 14 is formed has a strong response to incident x-ray photon energy. The regions of different thickness of the scintillator layer 14 perturb indicent x-ray photons differently. There is a certain probability that an x-ray photon will cause the release of a visible light photon when passing through a scintillator and that probability increases with increasing thickness of the scintillator. Further, higher energy x-rays are absorbed less by thinner scintillator material than they are by thicker scintillator material and x-ray energy, absorption and scintillator material thickness is non-linear. Figure 6 is a rear view of the scintillator plate illustrated in Figure 4 and a front view of the scintillator plate illustrated in Figure 5. The plate 13 provides forty nine regions, based around a repeating array of nine different pixel thicknesses, formed in a three by three block of regions. This arrangement provides that for any three by three group of nine regions the central pixel of the group is surrounded by eight regions each of which has a different thickness and that regions adjacent any one selected pixel are of a different thickness. The bottom right corner of the scintillator plate is numbered as a front view of Figure 5, and the top left corner is numbered as a rear view of Figure 4.

The difference in thickness between adjacent regions is approximately 200 micron in the illustrated examples described above.

Whilst the plate 13 provides forty nine regions based around a repeating array of nine different pixel thicknesses, the invention is not limited to this format. For example, the layout of the plate 13 may be based around a repeating array of four different pixel thicknesses in two by two array.

The prior art suggests that in an indirect x-ray detector the scintillator material should provide a flat response to incident x-ray energy. Such a scintillator material may be useful in either of the embodiments illustrated in Figures 4 and 5. However, it is preferred that the scintillator material should have a strong energy response, i.e. the number of visible photons produced will relate to both incident x-ray intensity and incident x-ray energy, possibly more strongly to incident x-ray energy than to incident x-ray intensity.

Figures 7 and 8 illustrate an alternative embodiment of the invention where instead of either the backing plate of the scintillator plate or the scintillator presenting regions of differing thickness, a scintillator of standard construction is used, with an interference plate 6 (which may also be considered to be a multi- absorption plate, i.e. different regions of the plate have different x-ray absorption capabilities), of tungsten for example, being placed between the object and the scintillator, or between the x-ray source and the object. Such a construction may be simpler and less costly to manufacture than a scintillator of the type illustrated in Figures 4 to 6. Further, in addition to manufacturing the interference plate such that regions thereof have different thicknesses, it possible that the interference plate may have uniform thickness, with the material difference between adjacent regions being provided by forming the individual regions of the interference plate of different materials.

The interference plate may comprise a substrate with the individual regions formed on or in the substrate. The individual regions may be formed in the base layer by etching or even machining the substrate.

The interference plate may be formed by 3d-printing.

The individual regions shown in Figures 4-8 may represent regions of different thickness.

The individual regions may be formed on the substrate by deposition, for example by a technique well known in the art as "lift-off. An advantage of such a technique is that the material deposited in the "lift-off process may be the same as the material from which the substrate is formed. The material difference between adjacent regions is the thickness of each pixel. Further, the deposited material may be different to the substrate material, providing for the material difference between adjacent regions to be in material type and/ or the material thickness.

Figures 9a and 9b illustrate an alternative construction of interference plate 16. In this example the interference plate 16 is formed of four layers of material 16a to 16d, such as foil. The first layer is not perforated. The second layer 16b includes apertures 16b' of a first width. The third layer 16c includes apertures 16c' of a second width, and the fourth layer 16d includes apertures 16d' of a third width. When stacked with the centres of the apertures 16b' to 16d' aligned the resulting structure has a cross-section 16'. When the layers 16a to 16d are stacked with the edges of the apertures aligned the resulting structure has a cross-section 16".

The structures 16', 16" each provide elongate regions of differing thickness. In Figure 9b, two of the resulting interference plates 16 are stacked with the apertures aligned perpendicular to one another. The resulting interference plate provides an array of square regions, wherein adjacent regions are of differing thickness.

Figure 10 illustrates another alternative arrangement of interference plate 16 comprising three layers 16f to 16h of wire mesh, each of differing mesh size. When stacked one on top of the other, in some regions incident x-rays will impinge upon the wires of the first layer 16f, in other regions incident x-rays will impinge upon wires of the second layer 16g, and in other regions incident x-rays will impinge upon wires of the third layer 16h. Further, in other regions incident x-rays will impinge upon a combination of some of the wires of more than one of the layers 16f, 16g and 16h. Further, there will be regions where no wire is present and hence x-rays incident on these regions will pass through unperturbed. Preferably, the wires are rectangular in cross-section.

In Figure 11 the interference plate 16 comprises a block of material that is square in plan view and which varies in thickness along two axes across the plate. Hence, the thickness of the material changes continuously across the plate. In this case the actual size of the region is determined by a pixellation grid, for example that of the detector camera. In the case of an interference plate 16 as illustrated in Figure 11 the difference in the mean thickness of adjacent regions must be sufficient to create a detectable difference in perturbation of an incident x-ray.

Referring now to Figures 12a and 12b, there is shown a further alternative construction of interference plate 60 comprising a first layer 61 and a second layer 63. The first layer 61 is formed of a silicon wafer and having formed therein a multiplicity of depressions 62. In the illustrated example the depressions have a depth of 800 micron. The depressions are formed by etching. It is known that strong alkaline wet etchants such as potassium hydroxide or tetra methyl ammonium hydroxide will preferentially etch certain crystal planes of silicon compared to others due to a difference in the bond strength of silicon atoms in the different crystal planes. The {111} crystal planes are amongst the most resistant to the etchants and so the {100} and {110} planes will be etched at far greater rates than the {111} planes. The silicon wafer from which the first layer 61 is formed is a { 100} oriented. A mask defining the array of depressions 62 is applied to a surface of the silicon wafer and an alkaline etchant applied. Where the alkaline etchant is in contact with the silicon it begins to etch down forming square based pyramidal shaped depressions 62. The sloping side- walls of the depressions 62 are the { 111} planes of silicon and thus are angled at 54.7 degrees compared to the surface of the { 100} silicon wafer. The etching process is allowed to proceed until the { 111} side walls converge to form the apex of a pyramid shaped depression 62.

The etchant used to create the depressions 62 was potassium hydroxide. The mask used to form the depressions 62 corresponds in shape to the plan view shown in Figure 12a. In the illustrated example, the depressions are set out on a 1mm x 1mm centre to centre grid. The distance between adjacent depressions 62 is approximately 50 microns.

The number of depressions may be increased or decreased by increasing or decreasing the distance between the centres of the depressions. When the distance between depressions is changed the depth of the depression and hence the size of the base of the depression will change, the size of the base being a function of the depth of the depression and the wall angle of 54.7 degrees. For example, the depth of each depression may be reduced to 100 microns.

Figures 12a and 12b illustrate a part of an interference plate. The interference plate might measure 26cm x 15cm for example, and the depressions may be on a grid that is smaller than the 1mm x 1mm centre to centre grid illustrated here.

The second layer 63 is formed of metal such as nickel, copper or tin. It is this metal second layer 63 which perturbs the x-rays incident upon it, each pyramidal protrusion providing a substantially infinite number of regions of different thickness as the thickness of the metal changes along the slope of the walls of the pyramid. The first layer serves to assist in manufacture of the interference plate and post manufacture to support and protect the metal layer 63. As can be seen from Figures 16a and 16b, the second layer 63 includes pyramidal shaped protrusions 64 and a backing plate 65. The second layer 63 is formed by deposition molten metal on to the surface of the first layer 61, the molten metal filling the pyramidal depressions 62 and forming a thin backing plate 65 (in the order of a few microns) covering the surface of the first layer 61. The metal of the second layer 63 between adjacent pyramidal protrusions may be considered as a region of different thickness to an adjacent region, perturbing the x-ray energy spectrum differently to the metal of the adjacent pyramidal protrusions.

The interference plate 60 may be attached to a scintillator by mechanical clamping or adhesive for example.

Interference plates (which may also be referred to as a multi-absorption plate) may be formed using three-dimensional printing techniques.

The detectors of the invention typically include a processor and advantageously a display. The display may be an alpha-numeric display, and the detector may be configured to give a measurement result or a material result, which may be displayed. It is conceivable that the output would be a sound. However, the detectors of the invention may form part of a control system where display of a result is not essential. For instance, the detector may be arranged to measure the thickness of a material and form part of a feedback loop to a device that influences the thickness of the material. A detector may be constructed as a hand held device. As mentioned above, where the detector is for use in detecting radio active materials typically it would not include a radio active source or a place to mount an object. Where the detector is constructed to test non radio active materials, the detector may include an x-ray source and may include a place to mount an object under test.

Figure 13 is a block diagram of a system according to an embodiment of the invention in which the detector 1 (which may be the detector of any of the previously described embodiments or other embodiments falling within the scope of the claims) provides an output to a data recording means 70. The data recording means is in communication with a data processor as is a database 71 in which data characteristic of known materials are recorded. The data recording means 70 and the database 71 are in communication with a data processor 72 which runs data processing software, the data processing software comparing information from the data recording means and the database to determine a material property of an object 3. A data output interface 73, such as but not limited to a VDU, is preferably included to which a determination of the data processing software may be outputted.

In another embodiment of the system illustrated in Figure 13, the detector 1 may output directly to the data processor 72, in which case the data recording means may be omitted, or the data recording means 70 may record data from the detector 1 via the data processor.

The detectors of the invention make use of readily available, low cost high resolution image detectors, that are not intended for use in x-ray imaging. By combining such detectors with a multi- absorption plate, or multiple detectors with different absorption plates x-ray detectors can be made very economically, albeit with performance limitations.

The detectors of the invention, in particular the embodiment illustrated in Figures la and lb using a single multi-pixel detector may be used advantaveously in applications where beam divergance effects are undesirable.

To determine a material property of an object 3 the x-ray source 4 is caused to direct an x-ray energy spectrum through the object 3, the MAP 2, scintillator plate 5, and optical coupling to impinge upon the multi-pixel imaging detector 1. Visible wavelength photons emitted by the scintillator are then analysed according to the following steps: Step (i) - The detector 1 is pixelated: the intensity of visible wavelength photons recorded by the detector for each pixel is compared with the recorded intensity for its adjacent pixels and the differences in intensity are recorded;

Step (ii) - The intensity of visible wavelength photons recorded by the detector for each pixel is compared with the recorded intensity for its adjacent pixels and the differences in intensity are recorded without the object 3 present;

Step (iv) - The current differences between recorded intensities between adjacent pixels as determined by the method steps (i) and (ii) are compared;

Step (v) - Following the method steps (i) to (iv) for at least one known material and storing the differences in a database; and

Step (vi) - Comparing the differences between recorded intensities for a substance under test with the differences between recorded intensities for known substances from the database.

In the illustrated examples, rather than performing the steps for every pixel, they may be performed for groups of pixels, where a group of pixels is aligned with a region of the structure that perturbs the x-ray spectrum, or the whole of the structure where the structure is uniform.

It is not necessary that all values are stored in the database. Where matching values are not recorded in the database, a value for a material under test may be interpolated.

In this specification the term x-ray shall be considered also to be a reference to gamma rays.

The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Furthermore, features of one embodiment illustrated and/ or described may be incorporated with features of one or more other embodiments where the possibility of such incorporation would be evident to one skilled in the art.

Claims

1. An x-ray/gamma-ray detection apparatus comprising at least one high resolution multi-pixel imaging detector, each pixel thereof having an area of not greater than 10 square microns, and a structure configured to perturb an x-ray /gamma-ray energy spectrum directed at the or each multi-pixel imaging detector.

2. An x-ray/gamma-ray detection apparatus according to Claim 1, comprising one multi-pixel imaging detector and wherein the structure comprises a plurality of regions, wherein adjacent regions are configured to pertub an incident x-ray/gamma-ray energy spectrum differently.

3. An x-ray/gamma-ray detection apparatus according to Claim 2, wherein the structure is an array of regions.

4. An x-ray/gamma-ray detection apparatus according to Claim 1, comprising a plurality of multi-pixel imaging detectors, each detector having a structure associated therewith.

5. An x-ray/gamma-ray detection apparatus according to Claim 4, wherein the structures associated with adjacent detectors are different.

6. An x-ray/gamma-ray detector apparatus according to Claim 5, wherein each structure is uniform or non-uniform.

7. An x-ray/gamma-ray detector according to any preceding claim, further comprising a scintillator.

8. An x-ray/gamma-ray detector according to Claim 6, comprising a plurality of scintillators, each scintillator associated with an individual multi-pixel imaging detector of a plurality of multi-pixel imaging detectors or a group of multi-pixel imaging detectors of a plurality of multi-pixel imaging detectors.

9. An x-ray/gamma-ray detection apparatus according to any preceding claim, further comprising an x- ray/gamma-ray source and/ or a position for an object under test.

10. An x-ray/gamma-ray detection apparatus according to any of Claims 7 to 9, further comprising an optical coupling between the structure and the multi-pixel imaging detector.

11. An x-ray/gamma-ray detection apparatus according to Claim 10, wherein the optical coupling is a fibre optic coupling or a lens.

12. An x-ray/gamma-ray detection apparatus according to any of Claims 7 to 11, wherein the optical path from the scintillator to the multi-pixel imaging detector is enclosed against ingress of visible wavelength light.

13. An x-ray /gamma-ray detection apparatus according to Claim 12, wherein the optical path from the multi-absorption plate to the detector is enclosed against ingress of visible wavelength light.

14. An x-ray/gamma-ray detection apparatus according to Claim 12 or 13, wherein said optical path is enclosed by an enclosure having an inner surface and the inner surface is selected to absorb visibile wavelength light.

15. An x-ray/gamma-ray detection apparatus according to any preceding claim, wherein the surface of the MAP facing the multi-pixel detector has an anti-reflective coating.

16. An x-ray/gamma-ray detection apparatus according to any preceding claims, further comprising a processor, the processor configured to integrate the signals of a plurality of pixels of the detector an generate an output for the plurality of pixels.

17. An x-ray/gamma-ray detection apparatus according to Claim 16, wherein the plurality of pixels is associated with the structure or a region of the structure.

18. A method of analysing at least one material property of an object comprising the steps of: a) Detecting an x-ray /gamma- ray energy spectrum emanating from or associated with an object using an x-ray /gamma- ray detection apparatus according to Claim 16 or 17;

b) Analysing the signal of each pixel of the multi-pixel imaging detector.

19. A method according to Claim 18, wherein analysis of each pixel is performed on summed signals of group of pixels, the group of pixels corresponding to the structure or a region of the structure.

20. A method according to Claim 18 or 19, wherein the method comprises the further step of recording the signals for individual pixels or groups of pixels of the detector and comparing the recorded signals with the recorded signals for adjacent pixels or groups of pixels.

21. A method according to Claim 20, comprising the further step of performing the step of Claim 20 without the object present.

22. A method according to Claim 21, comprising the further step of comparing the current differences between recorded signals between adjacent pixels or groups of pixels as determined by the method steps of Claims 20 and 21.

23. A method according to any of Claims 20 to 22, comprising the further step of following the method steps of Claim 20 for at least one known material and storing the differences in a database, and comparing the differences between recorded signals for an object under test with the differences between recorded signals in the database.

24. A method according to Claim 23, comprising the further step of producing at least one output representative of the at least one material property.

25. A method according to Claim 24, comprising the further step of displaying the at least one output on a display means.

26. An x-ray/gamma-ray detection apparatus substantially as shown in, and as described with reference to, the drawings.

27. A method of analysing one or more material property of an object substantially as shown in, and as described with reference to, the drawings.