GB2529375A - Multi-pixel x-ray detector apparatus - Google Patents

Abstract

X-ray detection apparatus comprises one multi-pixel imaging detector with pixels not greater than 10 microns, and a structure perturbing the x-ray energy spectrum directed at the multi-pixel imaging detector. The structure may have regions or layers of differing thickness. Examples include an interference plate, differences in a scintillator or backing layer, layers of foil, wire mesh, a continuously varying thickness and pyramidal depressions.

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. ilowever, 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.

[here 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, lagh resolution imaging detectors are used in various applications such as web cams and mobile phone cameras. These imaging detectors are vei cheap, and are capable of detecting x-ras, 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, lugh 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 typicaIIy provide in excess oft Mega pixels and have pixel size of 3 micron by 3 micron or less. Such detectors are fonned in a 3 mm by 3 mm chip. For example, high resolution multi-pixel imaglilg cameruts a having 8 Mega pixels with an individual pixel size of 1.5 niicron by 1.5 micron are commercially available.

The chip size for such a detector would be 4.5mm b 4.5mm.

Conventional x-ray dectors 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 dectors 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 prekrably the structure comprises a plurality of regions lying laterally of one another, and preferably in two orthogonal cI irections.

Preferably, the member configured to convert incident x-ray wavelength photons into emitted visible wavelength photons is a scintillator.

[he scintillator may include a scintillator layer and a backing layer.

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

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

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

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

Preferably, the protrusions or depressions are pyramidal in shape.

The structumv may comprise a non -metallic layer having a multiplicity of depressions formed therein, eacll depression filled with nletal. Preferably, die 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 situate d.

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 tllree regions.

Tile non-metallic layer Illay 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 compnse a substrate of even thickness, arid the individual regions may lie formed on a surilice thereof by buildingup discrete layers of material on adjacent regions. the number of layers and/or the materials of those layers may differ. Techniques such as PYD, electro-deposition or laser ablation may he used to form the individual regions.

In addition, the regional variation maybe 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 woulet be to stack a series of wire meshes together in a similar fashion to the foils such tli at variations in material thicknesses arc formed. This is simila r to techniques used to f)rm nciitra I density filters, Another alternative is to start with a certain thickness of material and cut out regions to create differing thicknesses. Ibis could he done by laser micro-machining or ion-beam milling amongst the many techniques.

Wieru the rriaterial 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 peints may each be considered to be regions configured to perturb the x-ray energy spectrum differently.

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

in some embodiments die x-ray detection apparatus includes or is associated with a database of recorded iiifoi-mation characteristic of known substances.

In some embodiments the x-ray detection apparatus includes or is associated wtli 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.

WIie ally 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 invendon is connecred.

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

[he method may comprise the further step of comparing the signals for individual pixels or groups of pixels of the detector with the mcorded 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 fir adjacent pixels or groups of pixels.

[he method may comprise the further step of performing die step of recording the sigIlais for hdividual pixels or groups of pixels of the detector and comparing the recorded sigiuls 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 iii a database, and comparing the differences between recorded signals for an object tinder 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 nieans.

Brief Description of the Drawings

in the Drawings, which illustrate preferred embodiments of x-ra detection apparatus according to the invention: Figure Ia is schematic representation of a multi-pixel non-imaging x-ray detector; Figure ibis a schematic representation of an alternative arrangement of non-imaging x-ray detector as shown in Figure ia; Figure 2 is a schematic representation of a x-ray detector comprising an array of multi-pixel x-ra 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; FigureS 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 vlew of the scintillator plate illustrated in Figure 5; Figure 7 is a cross-sectional view of all interferelice plate; Figure 8 is a front view of the nluln-mgloned structure, i.e. an interference plate illustrated in Figure 7; Figure 9a is an exploded vlew of all interfrrence plate built up from a number of layers of maturial; Figure 9b is a plan view oF component parts oF an interference plate oF the type illustrated in Figure Pa; Figure lOis an exploded vlew of an interference plate built up from a number of layers of wire mesh; Figure 11 is(i schematic represelitation of all interference plate having a thickness which varies ill two directions of the plate; Figure 12a is schematic, top pian and side views of aim altenlative embodiment of an interference plate; Figure 1 2h illustrates exploded side and schematic views of the embodiment illustrated in Figure 1 2a; and Figure 13 is a block diagram illustrating all 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 (I\1A2) 2.A scintillator may be situated between the I\1AP 2 and the detector 1, this being illustrated in Figure lb. Figure lb illustrates a non-imaging x-ray detecror, 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 I. lhe 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 scrntillator on to the detector 1.

The path between the scintillator 5, optical couphng 6 and detector 1 shouid 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 spectr light, for example it may be painted black, The surface of the MAP 2 facing the detector 1 nlay 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 silal from ally olle individual pixel is hkely to he accompanied by significant noise, to the extemit that the noise may render the information associated with all individual pixel of little use.

llowever, by integrating the signals from many of the pixels of the detector 1 into a single nieasurement, the noise can be removed to such an exrnnt that the measurement is useftml. Tile detector's ability to perform materials identification is emmlmammced by the MAP 2, which in effect divides the detector 1 into four segments, ill the illustrated example. lIme numnber 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 useftul measurement.

[he MAP 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 1 a or lb may be used in the oil iidustry For determining the proportions of water and oil in a mixture thereof, fbr example.

Another application would he 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, hut also what the radio active material is. Where radio active materials are being detected, the source 4 and ohjeet 3 are one and the same, that is die 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, hut difthrent to the absorption plate associated with its adjacent detectors 1.

Ilie detector arrays 10, 10' may include a scintillator, Each detector 1 may be associated with its owli discrete scintillator. An optical coupling may be provided and the assembly enclosed in the same manner as described iii relation to Figure lb. [he embodiments illustrated in Figures 2 and 3 have low resolution x-ray imaging capability. [he greater the number of detectors the better the x-ray image juality. In fact, the embodiments illustrated in Figures la and lb could be adapted to give low resolution imaging capabilities. [his 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 he six by six, giving thirty six groups of pixels, or ten by ten, giving one hundred groups ofpixels.

Alternative multi-absorption plates and scintillator plates are illustrated iii Figures 4 to 1 2b Figure 4 illustrates in cross-section a First embodiment of a scintillator plate 13 which compflses a scintillator layer 14 and a support layer 15. The scintillator layer 14 is ofa uniform material and has a iniiform thickness, Preferably, the material from which the scintillator layer 14 is fbrmed has a strong response to incident x-ray photon energy. 1-Iowever, the support layer 15, comprises a multiplicity of regions of differing thickness represented by numerals iSa to 15d. For the sake of clarity only a sample of regions are numbered.

Figure.5 illustrates in eros s-secti on a second cml)odimcnt of a scintilla tor phi te 3 which again comprises a scintillator layer 14 and a support layer 13. Ilie ftinction 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 (alunminium) 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 1 4a to 1 4d. For the sake of clarity only a sample of regions are numbered.

Preferably, the material from which tIme scintillator layer 14 is formed has a strong respommse to incident x-ray photon energy. The regions of different thickness of the scintillator layer 14 perturb indicent x-ray photons differently, Ihere is a certain probability that all x-ray photon will cause the release of a visible light photon when passing through a scintillator anti 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 scintdlator material thickness is non-linear, Figure 6 is a tear view of the scintillator plate illustrated iii Figure 4 and a front view of the seintillator 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. 1his 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 ate ofa different thickness, Ilie 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 iii the illustrated examples described above, \X1hilst the plate 13 provides forty nine regions based around a repeating array of nine different pixel thicknesses, the invention is not limited to tIns format. For example, the layout of the plate 13 may lie based around a repeating array of four different pixel thicknesses in two by two array.

1he prior art suggests that in an indirect x-ray detector the scintillator material should provide a flat response to incident x-ray eney. Such a scintillator material may be useful in either of the embodiments ifiustrated in Figures 4 and 5. However, it is preferred that the seintillator 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 hacking 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 difflrent 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 seintillator 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, Ihe interference plate may comprise a substrate with the individual regions Formed on or in the substrate. The iidividual regions may be loaned in the base layer by etching or even machining the substrate.

The interftrence plate may he formed by 3d-printing.

I'he individual regions shown in Figures 4-8 nay represent regions of different thickness.

The individual regions nlay 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 Thft-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 he different to the substrate material, providing for the material difference between adjacent regions to be in material type and/or die material tluckness, Figures 9a and 9b illustrate an alternative consrruction of interftrence plate 16. Tn this example the interference plate 16 is fi)rmcd of fiur layers of matenal 16a to 16d, such as foil, The first layer is not perforated. The second layer 16b includes apertures I 6b' ofa first width. The third layer I 6c includes apertures 16c' of a second width, and die fourth layer 16d includes apertures 16c1' of a third width. \Xi'hen stacked with the centres of the apertures 16b' to 16d' aligned the resulting structure has a cross-section 16'.

When die layers 16a to 16d are stacked with the edges of the apertures aligned die 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 all array of spiare regions, wherein adjacent regions are of differing thickness, Figure 10 illustrates another alternative arrangement of interference plate 16 compnsing three layers 161 to 16h ofwire mesh, each ofdifferingmesh size. When stacked one on top of the other, in some regions iicident x-rays will impinge upon the wires of the first layer 1 6I in other regions incident x-rays will impinge upon vires 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 16 16g and 161i. Further, there will he 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 coniprises ahlock of suaterial 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 reon 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 cli fference in the mean thickness of adjacent regions must be sufficient to create a detectable di ffereiice iii 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 ofa silicon wafer and having formed therein a multiplicity of depressions 62. In the illustrated example the depressions have a depth ot 81)0 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 (ill) crystal planes are amongst the niost resistant to the etchants and so the {l00} and {ii0} planes will be etched at far greater rates than die {ll1} planes. [he silicon wafer from which the first layer 61 is formed is a { I 00} oneiited.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 {1 11} planes of silicon and thus are angled at 54.7 degrees compared to the surface of the { 10(4 silicon wafer, Ihe etching process is allowed to proceed until the fill} side walls converge to form tIle apex ofa 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. Ilie distance between adjacent depressions 62 is approximately 50 microns, The numher of depressions may he 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 stie of the base being a Sanction of die depth of the depression and the wall angle of 54.7 degrees. For example, the depth I)feach depression may be reduced to 100 microns.

Figures 1 2a and 121) illustrate a part of an interference plate. The interference plate might measure 26cm x 15cm for example, and die depressions may be on a grid that is smaller than the 1mm x 1mm centre to centre grid illustrated here.

Ihe second layer 63 is formed of metal such as nickel, copper or tin. It is this metal second layer 63 which pcrturbs 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, die 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 ad jacent pyramidal protrusions may he considered as a region of different thickness to an adjacent region, perturbing the x-ray energy spectrum differently to the metal ofthe adjacent pyramidal protrusions.

The interference plate 60 may he 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 inchide 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 pan of a control system where display of a result is not essential, For instance, the dector 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 die dector is for use in decting 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 he 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. Ihe data recording means is in communication with a data processor as is a database 7! in which data characteristic of known nlateriais are recorded, the data recording means 70 and tile database 71 are ill collllllullicatioll with a data processor 72 which runs data processing software, tile data processing software comparing information fronl the data recording means and the database to determine a material propertvof an object IA data output interface 73, suci as but not limited to a \/DLT, is preferably included to \vhicll a deternlinatioll of the data processing software may be outputted.

In another enlhodinlent of the system illustrated in Figure 13, the detector 1 may output directly to tile data processor 72, ill whicil case tile data recording means may he olllitted, or the data recording means 71) may record data from tile detector 1 via the data processor.

Tile detectors of tile illvenfioll illake use of readiiy available, low cost lngh resolution image detectors, that are not intended for use in x-ray illlagmg. By combining sucil detectors with a multi-absorption piate, or multiple detectors with different absorption plates x-ray detectors can he made very economically, albeit \vitll performance limitations.

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

To determine a matermal property of an object 3 the x-ray source 4 is caused to direct an x-ray energy spectrunl tllrougll tile object 9, the i\LkP 2, scilltillator plate 5, and optical coupling to inlpinge upon tile nlulti-pixel imaging detector 1. Visible wavelengtll pilotons emitted by the scintillator are tilen analysed according to file 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 difterences 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 di Ffereiices between recorded intensities For a substance untler test with the differences between recorded intensities for known substances from the database.

In the illustrated examples, rather than perfbnuing the steps fr every pixel, they may he 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 he interpolated.

In this specification the term x-ray shall he considered also to he 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 (19)

1. Claims 1 An x-ray/gamma-ray detection apparatus comprisalg at least one iigii resolution multi-pixel ilnagmg detector, each pixel thereof having an area of not greater tItan 10 square microns, and a structure configured to perturb an x-ray! gamma-ray energy spectnim directed at the or each multi-pixel imaging detector.
2. 2.Anx -ray/gamma-ray detection apparatus according to Claim 1, comprisilig one mul ti-pixel imaging detector and wherein tile structure conp rises a plurality of regions, wherein adjacent regions are configured to pertub an incident x-ray/gamma-ray energy spectrum differently.
3. 3. An x-ray/gamma-ray detection apparatus according to Claim 2, wherein tile structure is an array of regions.
4. 4. An x-ray/gamma-ray detection apparatus according to Claim 1, conlprislllg a plurality of multi-pixel imaging detectors, each detector having a structure associated therewith.
5. 5. An x-ray/gamma-ray detection apparatus according to Claim 4, whenn the structures associated with adjacent detectors arc different.
6. 6. An x-rav/gaimna-ray detector apparatus according to Claim 5, wilereill each structure is uniform or non-un i fo nil.
7. 7. An x-ray/gamma-ray detector according to any preceding claim, further comprising a scmtillator,
8. 8. An x-ray/gamma-ray detector according to Claim 6, conlprisnng a plurality of scintillators, each scintillator associated with all 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 inlagillg detectors.
9. 9. An a-ray/ganmna-ray detection apparatus according to any preceding claim, filrther comprisIng an x-ray/gamma-ray source and/or a position for all object tinder test.
10. 10, An x-ray/gamma-ray detection apparatus according to ally of Claims 7 to 9, further conlprisnng an optical coupling between the structure and the multi-pixel imaging detector.
11. 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. 12, An x-ray/gamma-ray detection apparatus according to ally 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. 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. 14. An x-ray/gamma-ray detection apparatus according to Claim 12 or 1?,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. 15. An a-ray/gamma-ray detecdon apparatus according to any preceding claim, wherein die surface of the MAP facing the multi-pixel detector has an anti-reflective coating.
16. 16. An x-ray/gamma-ray detection apparatus according to any preceding claims, filrther comprising a processor, the processor configured to integrate the siia1s of a plurality of pixels of the detector and generate an output fbr the plurality of pixels.
17. 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. 18. A method of analysing at least one material property of an object compusing 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. 19. A method according to Claim 18, wherein analysis of each pixel is perfOrmed on summed signals of a group of pixels, tile group of pixels corresponding to the structure or a region of the structure, 20, A nietlioct according to Claim 18 or 19, wherein the method comprises the thrther step of recording the signals for individual pixels or groups of pixels of the deüetor arid comparing the recorded signals with the recorded signals for adljacent pixels or groups of pixels.21. A method according to Claim 20, comprising the further step of performing the sp of Claim 20 without the object present.22. A nietlioct according to Claim 21, comprising the further step of comparing the current differences between recorded signals between adjacent pixels or groups ofpixels as determined by the method steps of(. aims 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 die 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 die 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 displaymg the at least olle 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 refurence to, the drawings.