Abstract
A device for identifying materials on a conveyor belt (101) by means of X-ray fluorescence comprising an X-ray source (102), from which X-ray radiation (103) is guided onto material parts (104), comprising a detector head (107) containing an X-ray detector array (108) having a multiplicity of detector elements (113, 114, 115) arranged in a planar fashion for receiving X-ray radiation (105) and for converting said X-ray radiation into electrical charge signals, and also an electronic unit (109) for reading out and processing the charge signals, which comprises for each individual detector element a signal channel (120) having in each case: a discriminator unit (117) having at least two adjustable discriminator thresholds (116, 122) for detecting all Gaussian curve-like signals (119) whose amplitude is greater than one of the two or simultaneously greater than both discriminator thresholds, and also one counting unit (118, 121) per discriminator threshold for converting the signals into digital counting events,
wherein the individual detector elements of the X-ray detector array have a spatial resolution of 50 μm to 500 μm with a sensitivity to X-ray radiation in an energy range of between 500 eV and 30 keV, with an energy resolution of less than 0.5 keV at counting rates of up to 100 kcps and relative to an energy of 8.04 keV, the electronic unit comprises a signal channel for each individual detector element of the X-ray detector array,
and each discriminator unit for a specific detector element is in each case electrically connected to the discriminator units of the detector elements that are spatially directly adjacent to said detector element, wherein all the discriminator units are interconnected with one another via a digital and/or analog circuit in such a way that simultaneous occurrence of signals on more than one detector element can be identified and treated electrically separately.
Claims
1. A device for identifying materials, in particular metal parts such as scrap particles, on a conveyor belt (101) by means of X-ray fluorescence comprising an X-ray source (102), from which X-ray radiation (103) is guided onto the material parts (104) to be examined on the conveyor belt (101), comprising a detector head (107) containing an X-ray detector array (108) having a multiplicity of detector elements (113, 114, 115) arranged in a planar fashion for receiving X-ray radiation (105) scattered at the material parts or excited by the latter and for converting said X-ray radiation into electrical charge signals, and also an electronic unit (109) for reading out and processing the charge signals from the detector elements (113, 114, 115), which comprises for each individual detector element (113, 114, 115) of the X-ray detector array (108) a signal channel (120) having in each case: a discriminator unit (117) having at least two adjustable discriminator thresholds (116, 122) for detecting all Gaussian curve-like signals (119) whose amplitude is greater than one of the two or simultaneously greater than both discriminator thresholds (116, 122), and also one counting unit (118, 121) per discriminator threshold (116, 122) for converting the analog Gaussian curve-like signals (119) into digital counting events, wherein the individual detector elements (113, 114, 115) of the X-ray detector array (108) have a spatial resolution of 50 μm to 500 μm with a sensitivity to X-ray radiation in an energy range of between 500 eV and 30 keV, with an energy resolution of less than 0.5 keV at counting rates of up to 100 kcps and relative to an energy of 8.04 keV, the electronic unit (109) comprises a signal channel (120) for each individual detector element (113, 114, 115) of the X-ray detector array (108), and each discriminator unit (117) for a specific detector element (114) is in each case electrically connected to the discriminator units (117) of the detector elements (113, 115) that are spatially directly adjacent to said detector element (114), wherein all the discriminator units (117) are interconnected with one another via a digital and/or analog circuit (140, 142, 144, 146) in such a way that simultaneous occurrence of signals on more than one detector element (113, 114, 115) can be identified and treated electrically separately.
2. The device as claimed in claim 1, wherein the individual detector elements (202) disposed in a planar way are arranged in a strip-shaped fashion, in at least one (201), preferably a plurality (203, 204, 205) of groups parallel or collinear (206, 207) with respect to one another, and within a group the individual strips are aligned parallel to one another.
3. The device as claimed in claim 2, wherein first groups of detector elements (303, 304, 305, 306) are arranged orthogonally with respect to the conveyor belt direction and the individual strips of said group are arranged parallel to the conveyor belt direction and/or second groups of detector elements (307, 308, 309) are arranged parallel to the conveyor belt direction and the individual strips of said group are arranged orthogonally with respect to the conveyor belt direction.
4. The device as claimed in claim 3, wherein the X-ray detector array is constructed from a combination of first (406, 407) and second (403, 404, 405) groups of detector elements.
5. The device as claimed in claim 1, wherein at least some of the detector elements (501) are constructed from a silicon strip sensor having a substrate (502) with a thickness of more than 300 μm, in particular 300 μm to 2 mm.
6. The device as claimed in claim 1, wherein the discriminator thresholds of each individual detector element group (603, 604, 605, 606, 607) can be set independently of one another, and wherein as a result each group can be allocated one or a plurality of individual energy windows (613) for the detection of the impinging X-ray radiation.
7. The device as claimed in claim 1, wherein the discriminator units (722, 724, 726) of adjacent channels (714, 716, 718) are electrically interconnected with one another via an elimination unit (723, 725) for shared charges signals, wherein each of said elimination units (723, 725) has a parameterizable VETO discriminator threshold, and wherein the elimination unit (723, 725) has the effect that X-ray photons (701) arriving in the X-ray detector array are in each case not counted as an event if they have the consequence that a VETO threshold (715, 717) is exceeded by the electrical output signals (719, 720, 721) of two adjacent signal channels.
8. The device as claimed in claim 1, wherein the discriminator units (820, 822, 824) of adjacent channels (814, 815, 816) are electrically interconnected with one another via a correction unit (821, 823) for shared charges signals, and wherein said correction unit identifies simultaneously occurring Gaussian curve-like output signals (817, 818, 819) in adjacent channels, in such a case forms the sum of the output signal amplitudes, allocates the summation signal determined as a single event to that channel which exhibited the highest signal amplitude, and suppresses the registration of the output signal in the other channel.
9. The device as claimed in claim 1, wherein the X-ray detector array is constructed from n>2 first groups (915, 916, 917; 922, 923, 924) having in each case an identical strip spacing, wherein the strips are arranged offset from one group to the next group by the distance of the strip spacing divided by n.
10. The device as claimed in claim 1, wherein individual groups (1003) of detector elements in the TDI (“Time Delay Integration”) mode are operated synchronously with the instantaneous speed of the conveyor belt.
11. The device as claimed in claim 10, wherein the sub-channel method is applied to individual groups (1103) of detector elements, said method dividing the counting events of each individual physical detector element into more than two virtual signal channels.
12. The device as claimed in claim 1, wherein for reading out the digital signals from the counting units (118, 121), an FPGA (“Field-programmable gate array”) or an ASIC (“Application-specific integrated circuit”) or a freely programmable controller is provided, in each case in a manner preferably integrated in the detector head (107).
13. The device as claimed in claim 1, wherein one or a plurality of groups of detector elements (1308-1315) is (are) not operated as a spatially resolving 1D detector, but rather as a 0D detector arranged in a planar fashion, by virtue of the fact that the counting events of all the individual detector elements within said group(s) are added together and output as a single measurement value.
14. The device as claimed in claim 1, wherein each individual detector element of a group (1403, 1410) of detector elements is deactivatable.
15. The device as claimed in claim 1, wherein the X-ray detector is configured such that it can carry out continuously at least 2000 individual measurements per second.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIGS. 1-1 to 1-5 schematically illustrate a first embodiment of the device according to the invention.
[0047] FIGS. 2-1 to 2-3 schematically illustrate an alternative embodiment of the device according to the invention.
[0048] FIG. 3-1 to FIG. 3-2 show another alternative embodiment of the device according to the invention.
[0049] FIG. 4-1 shows an embodiment of the device according to the invention which is characterized by the fact that the X-ray detector array is constructed from a combination of first 406-407 and second 403-405 groups of detector elements.
[0050] FIG. 5-1 shows one embodiment of the device according to the invention in which the detector elements 501 are embodied as a silicon strip sensor.
[0051] FIG. 6-1 and FIG. 6-2 show one embodiment of the device according to the invention which is characterized by the fact that the discriminator thresholds of each individual detector element group 603 to 607 can be chosen independently of one another.
[0052] FIG. 7-1 to FIG. 7-3 illustrate the functioning of one embodiment of the device according to the invention which is characterized by the fact that the discriminator units of adjacent channels are electrically interconnected with one another via an elimination unit for shared charges signals.
[0053] FIG. 8-1 to FIG. 8-3 illustrate the functioning of one embodiment of the device according to the invention which is characterized by the fact that the discriminator units of adjacent channels are electrically interconnected with one another via a correction unit for shared charges signals.
[0054] FIG. 9-1 to FIG. 9-5 illustrate the functioning of one embodiment of the device according to the invention which is characterized by the fact that the X-ray detector array is constructed from n>2 groups having in each case an identical strip spacing, and the strips are arranged offset from one group to the next group by the distance of the strip spacing divided by n.
[0055] FIG. 10-1 to FIG. 10-3 illustrate the functioning of one embodiment of the device which is characterized by the fact that individual groups of detector elements are operated in the TDI (“Time Delay Integration”) mode synchronously with the instantaneous speed of the conveyor belt.
[0056] FIG. 11-1 to FIG. 11-3 illustrate the functioning of one development which is characterized by the fact that the sub-channel method is applied to individual groups of detector elements, said method dividing the counting events of each individual physical detector element into at least two virtual signal channels.
[0057] FIG. 12-1 shows one embodiment of the device which is characterized by the fact that the detector interface unit 1200 is preferably situated within the detector head 107.
[0058] FIG. 13-1 shows one embodiment of the device according to the invention which is characterized by the fact that one or a plurality of groups of detector elements is (are) not operated as a spatially resolving 1D detector, but rather as a 0D detector arranged in a planar fashion.
[0059] FIG. 14-1 shows one embodiment of the invention which is characterized by the fact that each individual detector element of a group of detector elements can be deactivated.
DETAILED DESCRIPTION
[0060] FIGS. 1-1 to 1-5 schematically illustrate a first embodiment of the device according to the invention.
[0061] FIG. 1-1 shows an X-ray source 102, which emits X-ray radiation 103 and irradiates an individual material piece 104 with said X-ray radiation, which material piece can be moved by means of a conveyor belt 101. The X-ray fluorescence radiation 105 excited by the material particle is usually guided through a collimation unit 106 and impinges on an X-ray detector head 107. The latter contains the X-ray detector array 108 and an electronic unit 109 for reading out and processing the signals from the X-ray detector array.
[0062] FIG. 1-2 shows the individual functional units within the detector head 107. Each individual detector element 114 of the X-ray detector array 108 is interconnected with an individual electronic sub-unit 112 consisting of a signal channel 120, a discrimination unit 117 and a plurality of counting units. The signal processing for detector element #N is illustrated by way of example. The signal channel converts the analog output signals of the detector element into Gaussian curve-like signals 119, which are converted into digital counting events in the discriminator unit. Each discriminator unit has at least two adjustable discriminator thresholds and each discriminator threshold is assigned a respective counting unit. In this example, the counting unit 118 counts all Gaussian curve-like signal events which exceed the discriminator threshold-1 116; counting unit 121 adds up all signal events which exceed the discriminator threshold-2 122.
[0063] FIG. 1-3 shows by way of example a histogram 126 having a typical frequency distribution of the amplitudes of the analog Gaussian curve-like time signals 119. The number (Counts) of the individual time signals which have a specific amplitude is plotted. Since the amplitude of the Gaussian curve-like signals is proportional to the energy (Energy) of the detected X-ray photons, this histogram is likewise an image of the energy distribution of the individual X-ray photons which have been detected in the detector element #N 114. Discriminator threshold-1 is normally chosen to the left of the maximum of the Gaussian curve-like histogram curve, for example at position 123. Discriminator threshold-2 is usually set to the right thereof, that is to say for example at position 125. In general, the aim is to detect all radiation events which lie in an energy window 124 defined thereby. It was assumed in this representation that no charge sharing occurs in the detector element.
[0064] FIG. 1-4 shows by way of example a histogram for the signal amplitudes at the location 119 and for the case where the X-ray radiation registered in detector element #N 114 is composed of X-ray photons of the energies E1, E2 and E3. If no charge sharing occurred, then the histogram would correspond to the profile 151. However, since charge sharing is normally unavoidable and generated charge carriers are consequently divided between adjacent detector elements, the real histogram shows a distribution as indicated in profile 150. Owing to charge sharing, the energy distribution of the X-ray photons having the energy E3 becomes asymmetrical and has low-energy components. The latter are superimposed with the energy distributions of the X-ray photons of the energies E1 and E2 and change the energy spectra thereof. The same applies to the energy distributions for the X-ray photons of the energies E2 and E1. These also become asymmetrical and in turn have low-energy components. The low-energy components of the photons of the energy E2 are superimposed with the energy distribution of the photons of the energy E1.
[0065] FIG. 1-5 schematically illustrates how the individual discriminator units of a first embodiment of the device according to the invention are coupled to one another. The discriminator units of spatially directly adjacent detector elements are interconnected with one another via electrical circuits such that simultaneous occurrence of signals on more than one detector element is identified, treated electrically separately and registered separately in the counting units. By way of example, the electrical circuit #N 142 is able to identify simultaneously occurring events in the detector elements #N-1 and #N (131 and 132) and to treat them separately. As a result of this electronic correction, the energy spectra registered by the individual discriminator units no longer contain any low-energy charge sharing components. If it is assumed by way of example that the energy distribution at the location 138 has a profile corresponding to 150 in FIG. 1-4, then the energy spectrum registered by the discriminator unit #N 143 after electronic correction has a profile in accordance with 151 in FIG. 1-4. The histograms for the individual photon energies appear completely separated from one another and no longer influence one another energetically.
[0066] One embodiment of the device according to the invention is illustrated in FIGS. 2-1 to 2-3. Accordingly, the individual detector elements 202 arranged in a planar fashion are strip-shaped and can be arranged in a single group 201 or in a plurality of groups 203, 204 and 205 parallel to one another. The individual detector element groups can also be arranged collinearly, as illustrated for example by 206 and 207. Within a group, the individual strips are preferably aligned parallel to one another.
[0067] FIG. 3-1 to FIG. 3-2 show one embodiment of the device according to the invention. By way of example, a material piece 302 is situated on a conveyor belt 301 and moves toward the detector elements at the speed v.
[0068] First groups of detector elements 303, 304, 305 and 306 are aligned orthogonally with respect to the conveyor belt direction. The individual strips of said groups are oriented parallel to the conveyor belt direction. Second groups of detector elements 307, 308 and 309 are arranged parallel to the conveyor belt direction. The individual strips of said second group are orthogonal with respect to the conveyor belt direction.
[0069] FIG. 4-1 shows one embodiment of the device according to the invention which is characterized by the fact that the X-ray detector array is constructed from a combination of first 406-407 and second 403-405 groups of detector elements.
[0070] FIG. 5-1 shows one embodiment of the device according to the invention in which the detector elements 501 are embodied as a silicon strip sensor whose semiconductor substrate 502 has a thickness D. The spacing of the individual detector elements has the distance p.
[0071] FIG. 6-1 and FIG. 6-2 show one embodiment of the device according to the invention which is characterized by the fact that the discriminator thresholds of each individual detector element group 603 to 607 can be chosen independently of one another, and that as a result each group can be allocated individual energy windows for the detection of the impinging X-ray radiation. It is assumed in this example that each of the groups mentioned has two globally adjustable discriminator thresholds 611 and 612 and thus an energy window 613. Consequently, a dedicated energy window E1, E2, E4 or E5 can be defined for each of the groups mentioned.
[0072] FIG. 7-1 to FIG. 7-3 illustrate the functioning of one embodiment of the device according to the invention which is characterized by the fact that the discriminator units of adjacent channels are electrically interconnected with one another via an elimination unit for shared charges signals.
[0073] FIG. 7-1 shows by way of example an X-ray photon 701 having the energy E.sub.0, which photon generates electrical charge carriers in the sensor substrate. On account of charge sharing, the charge carriers generated are distributed between two adjacent detector elements. A first subset 702 of said charge carriers is received by detector element 704, and a second subset 703 by detector element 705. The time signal 706 is generated at the output of the signal channel of detector element 704, and the time signal 707 is generated at the output of the signal channel of detector element 705. The sum of the signal amplitudes corresponds to the original photon energy E.sub.0. This embodiment of the device prevents the registration of an individual X-ray photon if the latter has the consequence that the preset VETO threshold is exceeded by the output signals of two adjacent detector elements simultaneously. Such a photon is accordingly not counted as an event in any of the individual counting units.
[0074] FIG. 7-2 shows the particular construction of the electronic interface unit 710 for this embodiment of the device according to the invention. A respective elimination unit is interposed between the discriminator units of two adjacent channels. In this example, discriminator unit #N is linked with the elimination units #N and #N+1. Each elimination unit additionally receives as input signals the two analog output signals of the adjacent signal channels and also a freely parameterizable VETO discriminator threshold. In the example, the output signals 719 and 720 and also the VETO threshold #N are passed to the elimination unit #N. The same correspondingly applies to the elimination unit #N+1. The output signal 720 is not registered and counted as a result if at the same time, in the case of output signal 719, an event occurs which exceeds the VETO threshold #N just like the output signal 720. The same correspondingly holds true if the output signals 720 and 721 simultaneously exceed the VETO threshold #N+1.
[0075] FIG. 7-3 shows the histogram profile for the output signal 720 of detector element #N. A typical energy distribution 730 is shown by way of example for the case where X-ray photons of the energies E1, E2 and E3 act simultaneously on the detector element #N (712) and the charge sharing effect occurs. The elimination units #N and #N+1 have the effect that the energy spectrum registered by the discriminator unit #N has a profile in accordance with 731 in FIG. 7-3. The histograms for the individual photon energies appear completely separated from one another and no longer influence one another energetically.
[0076] FIG. 8-1 to FIG. 8-3 illustrate the functioning of one embodiment of the device according to the invention which is characterized by the fact that the discriminator units of adjacent channels are electrically interconnected with one another via a correction unit for shared charges signals.
[0077] FIG. 8-1 shows by way of example an X-ray photon 801 having the energy E.sub.0, which photon generates the time signal 806 at the output of the signal channel of detector element 804 and the time signal 807 at the output of the signal channel of detector element 805 on account of charge sharing. This embodiment recognizes if charge carriers of an individual X-ray photon are distributed between two adjacent detector elements, and reconstructs the original photon energy by addition of the time signals 806 and 807. The reconstructed event is assigned to that detector element whose time signal had the highest amplitude. In the example, the reconstructed summation signal 808 is allocated to the detector element 805.
[0078] FIG. 8-2 shows the particular construction of the electronic interface unit for this embodiment of the device according to the invention. A respective correction unit is interposed between the discriminator units of two adjacent channels. In this example, discriminator unit #N is linked with the correction units #N and #N+1. Each correction unit additionally receives as input signals the two analog output signals of the adjacent signal channels. In the example, the signals 817 and 818 are passed to the correction unit #N. The same correspondingly applies to the correction unit #N+1. A signal 818 is not registered and counted as an event by discriminator unit #N if at the same time, in the case of 817, an event occurs whose amplitude is higher than that of the signal 818. In this case, the correction unit #N forms the sum of the amplitudes of the signals 817 and 818 and allocates this summation event to the discriminator unit #N-1. It can thus be registered by the counting units #N−1. The summation event is correspondingly allocated to the discriminator unit #N if the signal amplitude 818 is greater than that of signal 817.
[0079] FIG. 8-3 shows the histogram profile for the output signal 818 of detector element #N. A typical energy distribution 830 is shown by way of example for the case where X-ray photons of the energies E1, E2 and E3 act simultaneously on the detector element #N (812) and the charge sharing effect occurs. The correction units #N and #N+1 have the effect that the energy spectrum registered by the discriminator unit #N has a profile in accordance with 831 in FIG. 8-3. The histograms for the individual photon energies appear completely separated from one another and no longer influence one another energetically.
[0080] FIG. 9-1 to FIG. 9-5 illustrate the functioning of one embodiment of the device according to the invention which is characterized by the fact that the X-ray detector array is constructed from n>2 groups having in each case an identical strip spacing, and the strips are arranged offset from one group to the next group by the distance of the strip spacing divided by n.
[0081] FIG. 9-1 shows by way of example a material piece 902 which moves toward a detector element group 903 at the speed v. The spacing of the detector elements amounts to the distance p.
[0082] FIG. 9-2 shows in row B1 the detector elements of the group 903 which have the spacing p and which detect the X-ray fluorescence radiation emitted by the material piece 902. In this example, the material piece generates N X-ray photons per unit time. Each detector element is assigned, as illustrated in row C, a storage cell in which the number of registered X-ray photons is entered. In rows A1 to A6, the letter x denotes different possible positions of the material piece 902. For each of the positions A1 to A6, the detector element detects N counting events as illustrated. In this example, the achievable spatial resolution thus corresponds to the distance p1, which is equal to the distance p.
[0083] FIG. 9-3 shows by way of example a material piece 902 which moves toward three detector element groups 915, 916 and 917, which are parallel to one another, at the speed v. The spacing of the detector elements within each group amounts to the distance p. The detector elements of the groups 915, 916 and 917 are arranged offset by ⅓ p in each case.
[0084] FIG. 9-4 shows in row B1 the detector elements of the group 915, in row B2 the detector elements of the group 916 and in row B3 the detector elements of the group 917. Each of the detector elements is assigned, as illustrated in row C, a storage cell in which the number of registered X-ray photons is entered. If the material piece 902 is situated at the positions A1 or A2, then in the three detector elements as illustrated in each case N counting events are registered and assigned to the corresponding storage cells. In this example, the spatial resolution achievable following application of suitable interpolation methods corresponds to the distance p3, which is significantly smaller than the distance p.
[0085] FIG. 9-5 shows that this functional principle can also be applied to the high-resolution spatial determination in the conveyor belt direction. The material piece 902 moves toward the groups 922, 923 and 924, which are arranged offset by the spacing p/3.
[0086] FIG. 10-1 to FIG. 10-3 illustrate the functioning of one embodiment of the device which is characterized by the fact that individual groups of detector elements are operated in the TDI (“Time Delay Integration”) mode synchronously with the instantaneous speed of the conveyor belt.
[0087] FIG. 10-1 shows by way of example a material piece 1002 which moves toward a detector element group 1003 at the speed v. The group consists of M detector elements. The spacing of the individual detector elements amounts to the distance p.
[0088] FIG. 10-2 illustrates by way of example the functioning of the TDI method. The illustration shows the spatial position of the material piece 1002 relative to the individual detector elements #1 to #M (row A) and at the points in time t0, t1 and tn. At the point in time t0, the detector element #1 registers the number of N11 X-ray photons, and the detector element #2 registers the number of N12 photons. N11 is added to the existing content of storage cell #j+1 (row D), and N12 to the content of storage cell #j+2. Exactly the same procedure is adopted at the subsequent points in time. The X-ray photons emitted by the material piece 1002 are in turn added to the storage cells #j+1 and #j+2. At the point in time t1, therefore, the counting rates N21 and N22 are added to the storage cells #j+1 and #j+2, and at the point in time tn, the counting rates Nn1 and Nn2 are added to the storage cells #j+1 and #j+2.
[0089] FIG. 10-3 shows by way of example an intensity profile plotted against the conveyor belt direction, which intensity profile was measured by the detector element group 1003. The measurement was carried out without the TDI method in case A and with application of the TDI method in case B. In case B, the intensity fluctuations e1B for the detected material piece 1002 and the intensity fluctuations for the measured background radiation e2B, on account of the TDI method, are significantly smaller than those in case A. The spatial position and the material composition of the material piece 1002 can thus be determined significantly better by applying the TDI method.
[0090] FIG. 11-1 to FIG. 11-3 illustrate the functioning of one development which is characterized by the fact that the sub-channel method is applied to individual groups of detector elements, said method dividing the counting events of each individual physical detector element into at least two virtual signal channels. The method is carried out synchronously with the instantaneous speed of the conveyor belt and can be applied with or without the TDI method.
[0091] FIG. 11-1 shows by way of example a material piece 1102 which moves toward a detector element group 1103 at the speed v. The group consists of M detector elements. The spacing of the individual detector elements amounts to the distance p.
[0092] FIG. 11-2 illustrates by way of example the functioning of the sub-channel method with simultaneous application of the TDI method. The illustration shows the spatial position of the material piece 1102 relative to the individual detector elements #1 to #M (rows A1 to A4) and at the points in time t.sub.1, t.sub.2, t.sub.K and t.sub.K+1. In this example, each real detector element is divided into K virtual detector elements having a virtual spacing of p/K. X-ray photons are in each case measured for a time duration T and allocated to the individual storage cells as follows. At the point in time t.sub.0, the detector element #1 registers the number of N11 X-ray photons, and all other detector elements register the counting rate 0. N11 is added to the existing content of storage cell #j+1 (row D1). At the point in time t.sub.2, the counting rate N12 is detected and counted toward the content of storage cell #j+2 (row D2). At the point in time t.sub.K, the last sub-channel of detector element #1 is detected, the counting rate N.sub.1K is determined and allocated to storage cell #j+K (row D3). At the point in time t.sub.K+1, the first sub-channel of detector element #2 is reached. The counting rate N21 is added to storage cell #j+1 (row D4).
[0093] FIG. 11-3 illustrates the mode of action of the sub-channel method for the case where the individual detector elements are divided for example into 5 virtual signal channels. The illustration shows in rows D1, D2, D3 and D4 the intensities summed in the storage cells for four different spatial positions A1, A2, A3 and A4 of the material piece 1102 that are assumed at the point in time t.sub.0. The exposure duration corresponds to the time T. If the spatial position of the material piece 1102 differs in steps by the distance p/5 toward the right, as illustrated in cases A1, A2, A3 and A4, then in the data memory the measured intensities are likewise offset toward the right by one storage cell. With this method, therefore, it is possible to register changes in the X-ray photon intensity even actually within an individual detector element.
[0094] FIG. 12-1 shows one embodiment of the device which is characterized by the fact that the detector interface unit 1200 is preferably situated within the detector head 107. In a customary manner, an FPGA (“Field-programmable gate array”) or an ASIC (“Application-specific integrated circuit”) or a freely programmable controller is used for reading out the digital signals from the counting units which are situated in the electronic unit 109.
[0095] FIG. 13-1 shows one embodiment of the device according to the invention which is characterized by the fact that one or a plurality of groups of detector elements is (are) not operated as a spatially resolving 1D detector, but rather as a 0D detector arranged in a planar fashion. In the example illustrated, the material pieces 1302 and 1303 are moved by the conveyor belt. The X-ray detector arrays 1308 to 1315 are operated in each case as a 0D detector. Within an X-ray detector array, for this purpose the counting events of the individual detector elements are added together and output as a single measurement value. If a plurality of energy windows were defined, such a measurement value is determined and output for each energy window.
[0096] FIG. 14-1 shows one embodiment of the invention which is characterized by the fact that each individual detector element of a group of detector elements can be deactivated. By way of example, in the groups 1403 and 1410 the detector elements in the regions A1, A3, B1 and B3 were deactivated. The active area thus comprises only the regions A2 and B2.
