GB1603271A – X-ray detector
– Google Patents
GB1603271A – X-ray detector
– Google Patents
X-ray detector
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Publication number
GB1603271A
GB1603271A
GB11665/78A
GB1166578A
GB1603271A
GB 1603271 A
GB1603271 A
GB 1603271A
GB 11665/78 A
GB11665/78 A
GB 11665/78A
GB 1166578 A
GB1166578 A
GB 1166578A
GB 1603271 A
GB1603271 A
GB 1603271A
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GB
United Kingdom
Prior art keywords
scintillation
radiation detector
detector assembly
detection means
electron
Prior art date
1977-03-28
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB11665/78A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Philips Gloeilampenfabrieken NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1977-03-28
Filing date
1978-03-23
Publication date
1981-11-25
1978-03-23
Application filed by Philips Gloeilampenfabrieken NV
filed
Critical
Philips Gloeilampenfabrieken NV
1981-11-25
Publication of GB1603271A
publication
Critical
patent/GB1603271A/en
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Expired
legal-status
Critical
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Classifications
G—PHYSICS
G01—MEASURING; TESTING
G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
G01T1/16—Measuring radiation intensity
G01T1/161—Applications in the field of nuclear medicine, e.g. in vivo counting
G01T1/164—Scintigraphy
G01T1/1641—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras
G01T1/1645—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras using electron optical imaging means, e.g. image intensifier tubes, coordinate photomultiplier tubes, image converter
Description
PATENT SPECIFICATION
( 11) 1 603 271 ( 21) Application No 11665/78 ( 22) Filed 23 March 1978 ( 31) Convention Application No 7703294 ( 32) Filed 28 March 1977 in ( 33) Netherlands (NL) ” ( 44) Complete Specification Published 25 November 1981 ( 51) INT CL 3 HO 1 J 31/49 ( 52) Index at Acceptance Hi D 18 L 418 LY 34 4 A 1 4 A 2 A 4 A 2 Y4 F 6 A 4 F 6 B4 F 6 Y4 HX 4 HY 4 K 2 B 4 K 2 C4 K 2 Y 4 K 3 B 4 M H 1 K l EB 251 B 2520 4 C 2 A5 B 2 5 B 5 9 B 1 9 B 1 A9 B 4 A 9 D 1 9 R 2 EBA ( 54) X-RAY DETECTOR ( 71) We, N V PHILIPS GLOEILAMPENFABRIEKEN, a limited liability Company, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, the Netherlands, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and
by the following statement:-
The invention relates to a radiation detector, comprising a scintillation element and an intensifying light detection device for the detection of scintillation light produced in the scintillation element.
A radiation detector of this kind is known from U S Patent Specification 3,866,047 (Hounsfield.
February 11 1975) An X-ray detector described therein comprises an array of scintillation crystals, a photomultiplier being coupled to each scintillation crystal In order to find room for the photomultipliers each successive photomultiplier is arranged opposite a corresponding one of three differently orientated faces of the scintillation crystals A radiation detector can thus be realized in which the centre-to-centre distance of successive channels is reduced to for example 8 mm Upon detection of incoming Xradiation, a difference is liable to occur between the channels with respect to each other, notably between channels to be read out laterally with respect to the incident X-ray beam and those which are to be read out along the direction of said beam The stability of the photointensifier tubes used is not sufficient for all applications.
notably when measured over a prolonged period of time Correction in this respect though not impossible would in any case be very complex.
Moreover, the dimensions of the photomultiplier tubes used therein are such that the resolution in a direction along a linear array of detectors is insufficient for given applications, in spite of the alternating arrangement Furthermore, the use of photomultiplier tubes implies an excessive limitation of the dynamic range of the detector for many applications.
The invention has for an object to provide an improved radiation detector.
According to the invention there is provided a radiation detector assembly for forming a plurality of adjacent individual radiation detectors in computed tomography apparatus, said assembly comprising scintillation means, and amplifying light detection means for detecting scintillation light produced in the scintillation means to provide a corresponding output, said light detection means comprising photoemissive means, optically coupled to said scintillation means, and semiconductor-junction electrondetection means located in a vacuum chamber provided with an electron-optical system arranged so that electrons locally emitted by a respective photoemissive region in response to said scintillation light, are accelerated towards, and generally concentrated at a corresponding semiconductor junction region to provide an individual output signal with photoemissive current amplification, wherein said scintillation means comprises a plurality of individual scintillation elements which are screened from one another with respect to scintillation radiation, each scintillation element being optically coupled to a corresponding photoemissive region forming a photocathode in a said electron-optical system.
The scintillation light detectors in the form of photomultiplier tubes are replaced in a detector embodying the invention, by a system in which photo-electrons generated by the scintillation light are accelerated and subsequently detected by a semiconductor-junction electron detector so that each incident electron generates a plurality of charge carriers The stability as well as the sensitivity and the dynamic range of the radiation detector can thus be substantially improved A detector assembly embodying the invention can take the form of, for example, a plurality of modules each comprising a group of individual light detection channels in a common housing, in order to form a multiple detector device in which a comparatively small centre-to-centre distance exists between the individual radiation detection 1 603 271 channels The light-detector housing in one embodiment of the invention are mounted so as to be demountable, either together with the associated scintillation elements or on their own, so that should one of the channels become defective, only the relevant housing need be replaced.
The detector module of a further embodiment comprises a housing including a plurality of windows for the scintillation light formed in one side, the inner surface of each said window supporting a photocathode, whilst an electrode system which is accommodated within the housing, projects the photoelectrons emitted by the photocathode onto an active surface area of a semiconductor electron detector The semiconductor electron detector of a further embodiment contains a block of silicon having a pn transition which is situated at a comparatively small distance below the surface, the semiconductor detector being shielded from alkali elements from the photocathode by means of, for example, a poly amide layer or by a nitride treatment so that an extremely effective, protective sealing layer of silicon nitride is obtained.
For the sake of clarity, the terms light or luminescent light are used for the scintillation radiation which is produced in the scintillation element by the radiation to be detected, which latter can comprise X-radiation or gamma radiation: however this is not intended to imply a restriction to the visible wavelength range, but to include scintillation radiation which is situated outside the visible range notably ultraviolet radiation.
In order that the invention may be clearly understood and readily carried into effect, various embodiments of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings of which:Figure 1 is a sectional view of a part of a detector embodying the invention, Figure 2 shows an arrangement of light conductor scintillation elements forming part of an embodiment and whereby a single row of scintillation elements is converted into a multiple series of read out channels, Figures 3 and 4 are front views of detector modules, comprising 9 and 16 light detection channels, respectively, Figure 5 is a perspective view of a modular construction of a detector embodying the invention.
Figure 6 shows a scanning X-ray examination apparatus, including a detector embodying the invention.
Figures 7 to 9 are diagrammatic cross-sectional views of a semiconductor electron detector with nitride protecting layer and embodying the invention, in successive stages of manufacture.
and.
Figures 10 and 11 are cross-sectional views in two successive stages of manufacture of a modified embodiment of the electron detector shown in figures 7 to 9.
A detector device embodying the invention is illustrated diagrammatically in Figure 1 and comprises a series of scintillation elements 1 which are mounted between supports 3 and 5 to 70 receive X-radiation incident from the direction of view, i e a direction normal to the drawing of Figure 1 The scintillation elements may be made, for example, of crystals of Nal, Cs I, Bi 4 Ge 3012 or of one of thematerials referred to in 75 UK Patent Application Number 11666/78 (Serial NO 1603 272) Use can also be made of scintillation elements in which a powdery scintillation material is buried in a suitable support of, for example, glass or a synthetic material which has a 80 low absorption factor for the scintillation light.
Powdery scintillation material can also be used as a powder/liquid mixture contained in a holder, as a cover layer on a transparent support which can then act as a light conductor, or in the sintered 85 condition where usually adequate transparency is obtained.
The scintillation elements are laterally read out in this case, i e via end faces 7 All side faces which are not to be irradiated or read out are 90 shielded in order to reduce cross-talk, by means of a layer which absorbs the radiation to be measured and which is impermeable to the scintillation light, i e preferably an internal reflective layer with respect to the scintillation 95 light The cover layer is transparent for radiation for the front faces 8 which face the radiation to be detected Preferably, no cover layer is provided on the faces to be read out, because these faces must be suitable to transmit as much luminescent 100 light as possible Between the scintillation elements there may be provided a radiation absorbing material, so that the scintillation elements are protected against indirect irradiation such as by stray radiation and secondary 105 radiation For example, the scintillation elements can be accommodated in a housing, for example, of aluminium; obviously the end faces to be read out then remain uncovered, but the housing may enclose the radiation entrance faces In order to 110 ensure that as much as possible of the scintillation light is effectively intercepted, it may be advantageous to construct the scintillation elements as light conductors; for this purpose scintillation material, for example, is embedded 115 in or is locally added to a glassy support having a shape adapted for optimum light conduction For the sake of clarity, Figure 1 shows only a single row of scintillation elements, but in practical detection devices embodying the invention it 120 may be advantageous to use a plurality or rows of scintillation elements which are preferably staggered with respect to each other For example, Figure 2 is a sectional view, taken parallel to a plane of incidence of the radiation to 125 be detected, of an embodiment comprising two rows of scintillation elements Any desired shape, for example, square, rectangular, round.
triangular, elliptical etc, can be used for the section of the scintillation elements for reasons of 130 1 603 271 optimum radiation absorption, light yield or cost.
Besides for the purpose of reducing cross-talk between the scintillation elements themselves, partitions can be provided between the scintillation elements in order to reduce the adverse effect of stray radiation, said partitions being arranged parallel to the direction of the incident radiation and acting as a collimator for stray radiation These partitions may form part of the envelopes of the scintillation elements and may be extended in the direction of the radiation source as far as beyond the scintillation elements, in order to serve as a collimator for the incident radiation Alternatively or additionally, a separate collimator can be employed the apertures thereof being adapted to the geometry of the scintillation elements.
In the embodimentshow, the supportingplates 3 and 5 are provided with bores 9 wherethrough ends of the scintillation elements project, for example as far as beyond the outer surfaces of the supporting surfaces Thus, firm mounting of the scintillation elements is ensured Each of the scintillation elements is read out on only one side in this case i e per group of elements alternately on the lower side and the upper side thereof (viewed in the drawing) For end faces of the elements which are not be read out, the bores 9 in the supporting plates preferably do not extend through the entire supporting plate.
The detector faces 7 of the scintillation elements can be directly coupled, for example by means of a suitable intermediate immersion liquid, to a measuring element for measuring the scintillation light However, it may be advantageous to insert an optical conductor whereby.
for example the light can be collimated or dispersed Thus a transverse displacement can be effected for example by means of a fibre-optical light conductor so as to enable a more advantageous geometry for the detection of the scintillation light to be selected Instead of a fibreoptical light conductor, use can alternatively be made of for example an elliptical light conductor a face of the scintillation element to be read out then being located as closely as possible to a first focal point of the ellipsoid, the radiation measuring element having an entrance face located adjacent the second focal point.
Alternatively the scintillation element itself may be constructed to be an ellipsoid, a concentration of scintillation material then being provided, for example, around a first focal point, the entrance window for the light measurement being mounted around the second focal point of the ellipsoid Use can then be made of the said scintillation elements where the scintillation material is embedded in anon-absorbingsupport.
When use is made of light conductor elements between the scintillation element and the measuring device for the scintillation light, for example a single row of scintillation elements can be converted into a plurality of adjacently situated rows of measuring windows, so that more space is available for further light detection and cross-talk can be further reduced Figure 2 shows an embodiment in which a single row of scintillation elements 31, being accommodated in an arrangement of light conductors 33, can feed light from different parts of the element 31 respectively onto four rows of light detection elements 35 Thus, two of these four rows of light channels are adjacently arranged and two rows are arranged one opposite the other When a plurality of these foursomes are arranged one behind the other in a direction transversely of the plane of the drawing, a multi-channel detector can be constructed The scintillation material 31 is again concentrated around each respective focal point relating to the corresponding light conductor It may be advantageous to form the light conductors from one of the fluorescent materials as described in UK Patent Application Number 11666/78 (Serial Number 1603272), so that the radiation yield can be increased without giving rise to disturbing afterglow In Figure 2, the four light conductors are situated in pairs one behind the other in a single row in the vicinity of the scintillation material 31, and the measuring devices 35 may all be situated on one plane or may be staggered with respect to each other.
In the embodiment shown, the scintillation elements are group-wise read out, alternately on each side However, it is alternatively possible, if necessary by displacement of the entrance windows with respect to the scintillation elements, to arrange light conductors so that all scintillation elements are read out on one side In a further embodiment of the invention, scintillation element can then be combined as desired, but the signals can also be separately used, thus enabling simultaneous measurement of two slices of an object under examination If desired, the scintillation element can be divided optically in two by means of a partition which is preferably arranged halfway along the length dimension.
The measuring devices for measuring the light produced in the scintillation elements are groupwise combined in modules 11 in the preferred embodiment shown A module of this kind comprises, for example, nine channels which are arranged as shown in Figure 3, so that in this case an entrance window 13 is locted directly in front of each scintillation element 1 The entrance windows 13 are each provided on the inner surface thereof, with a cathode 15 which is sensitive to the scintillation light to be detected An entrance plate 17 of the modules may be made of metal or of glass, preference being given to glass, or at least of an electrical insulator which can be metallized internally and externally, if desired.
The windows 13 are provided in this entrance plate; in the case of a metal entrance plate, they are provided as separate, transmitting windows, whilst in the case of a glass plate they are formed by recesses which are integral with the plate.
Preferably, the windows are constructed to be concave on the inner surface, i e the surface on which the photocathode is located In order to minimize cross-talk on radiation transmission 1 603271 from the scintillation elements to the photocathodes when use is made of glass supporting plates, these plates are preferably constructed to be absorbing for the relevant scintillation light S between the windows In a preferred embodiment the windows and the supporting plate are made of glass having a comparatively high refractive index The windows may be sealed in the supporting plate as separate plates; an optical barrier may then be included between the windows and the supporting plate The photocathodes can be formed together for each in the housing module The inner surface 20 of the entrance plate 17 is then provided, if necessary, with an electrically conductive layer which is light-empermeable, at least in the regions between the windows.
Figure 4 shows a further embodiment of a detector module 11 which comprises sixteen measuring channels 13 arranged so that a scintillation element is directly associated with each measuring channel and can be irradiated e g.
from above or below as shown in Figure 4, only by the X-radiation to be detected Therein, the connection between the windows of successive modules is not seamless, i e without disturbance of the mutually equal distances between the windows Thus in this 16-fold, four-row module.
the effective distance between the windows of two modules which are situated opposite each other at an angle sometimes amounts to 3 times and sometimes to 5 times the minimum distance occurring between windows in the row direction.
The figure shows that this construction enables efficient use of the space inside the module housing If the use of four rows of scintillation elements is undesirable this window orientation can still be maintained by adopting this window configuration on the basis of one or two rows of scintillation elements and by using light conductors.
Opposite each of the photocathodes there is arranged an electron detector 19 comprising a semiconductor-junction electron detector formed in a semiconductor material having a Fermi gap of at least approximately 0 6 e V, and which is shielded by an aperture plate 21 except for a sensitive surface area 23 The aperture plate 21 can also serve as a high voltage electrode for accelerating the photoelectrons released by the photocathode A signal recording device 25 is diagrammatically shown to be arranged in the vicinity of the electron detectors said device recording signals derived from the electron detector and supplying the signals, preferably after conversion from simultaneous input to sequential output for further processing to subsequent electronic circuits (not shown).
For a given distance between the photocathodes and the aperture plate for the electron detectors, and for a given acceleration voltage to be applied for example, at least 10 KV, suitable focussing of the photocathode on the electron detector can be achieved by suitable shaping of electron-optical system formed by the photocathode and the edges of the aperture plate, without further electron-optical elements per channel being required for each channel A sleeve 27 constitutes, together with the entrance plate, a vacuum tight box in which a customary pressure for image intensifier tubes prevails.
Each of these boxes or modules is detachably connected to the supporting plates 3 and 5, the windows 13 being situated opposite the relevant end faces 7 of the scintillation elements This method of mounting does not require very high accuracy; thus, adjustment within, for example, approximately 0 5 mm with respect to the supporting plate, to be realized, for example, by way of ridges 29 provided thereon, is sufficient.
When the entrance windows and the scintillation elements are assembled, an immersion oil, a poly amide film a silicon film, a ductile transparent rubber layer of a similar material may be provided therebetween in order to increase the radiation transmission The refractive index (Nt) of the contact material is preferably higher than that (Nk) of the scintillation element and lower than that (Nv) of the window This demonstrates that for the window use is preferably made of a material having an as high as possible a refractive index It is also advantageous to construct the window to be as thin as possible, the more so because additional radiation loss due to a thick window may give rise to cross-talk A suitable material for the entrance plate, both as regards the formability as well as strength, is the sotermed glassy carbon The preferably round windows of the photocathodes have a diameter of, for example, from 5 to 10 mm and a spacing of at least from I to 5 mm The distance between the photocathodes and the electron detectors is for example, from 5 to 10 mm and the aperture for each of the electron detectors has a diameter of approximately 1 5 mm.
In a further embodiment, the scintillation elements are integral with the light detectors and the photocathodes are arranged, for example, directly on the read out faces of the scintillation elements The shape of the scintillation elements and the exit windows thereof can then be adapted to the desired shape of the photocathodes The electron detectors are preferably formed so that a comparatively thin diffusion layer occurs as a detection transition, because in this region the energy loss for the photoelectrons to be detected is a minimum For a detailed description of this type of electron detector, reference is made to the article Electron Bombarded Semiconductor Devices, proc IEEE, vol 26, No 8, 1964, pages 119-1158 The electron detector should furthermore be properly shielded against alkali elements such as Cs Na, K, which may be released during the formation of the photocathodes Besides the shielding of the detector with a cover layer which is impermeable to contaminating materials, such as by the said nitriding, a suitable provision against contamination of the detector can be effected by arranging the detector so that the pn transition formed therein is situated in a region 1 603 271 adjacent the surface which is remote from the entrance surface The contaminating substances then have more difficulty in reaching the pn transition The surface to be struck by the electron beam can also be shielded.
In modules as used in various embodiments of the invention the photocathodes are formed only after the remainder of the module has been completely assembled i e also after mounting the electron detectors The amount of alkali elements released is much larger during the formation of the photocathodes than during later operation; this makes the process of formation utilizing transfer techniques, attractive, notably in cases where use is made of semiconductors which are not shielded very well Also in the case of properly shielded semiconductor detectors, for example by means of the said nitrification, it mav be advantageous for further reduction of the risk of contamination to maintain the diodes outside the atmosphere prevailing, for example, by transfer techniques during the formation of the photocathode In a preferred method of assembling detector modules embodying the invention, the electron detectors are covered by removable shields during the formation of the photocathode in order to avoid the comparatively complex and expensive transfer technique The aperture plate with comparatively small apertures for each of the electron detectors readily permits such shielding, for example by a double construction of this aperture plate it being possible to close and open the apertures by displacement with respect to each other Alternatively, a thin foil may be arranged across the aperture plate, said foil being either removed after the formation of the photocathodes or being suitably transparent for the electrons to be detected A comparatively favourable method utilizes spheres which close the apertures during the photocathode formation process and which are subsequently removed via an exhaust tube.
Figure 5 shows a modular construction where the scintillation elements 1 form part of amodule.
The slide 51 is rigidly connected to a block 55 comprising pin holes 57 for adjustment of the module A recess 61 in a block 63 also supporting a slide for scintillation elements, enables unimpeded linking of blocks in conjunction with a corresponding recess 65 in the block 55 into an assembly which can take the form of an arc of a circle In a recess 69 in the block 55 and in a recess 71 in the block 63 further slides with scintillation elements can be connected in succession on both sides The construction of the slides with scintillation elements is such that a seamless transition is realized between the slides for the two rows of scintillation elements A module like the module 11 shown in Figure 3 can then be provided in each of the blocks with a suitable fit preferably by means of abutment faces.
The detection channels in each of the modules then adjoin the scintillation elements provided in a slide This results in a satisfactory modular construction of a detector device embodying the invention in which the scintillation elements are also arranged in modular fashion An advantage is thus obtained in that, besides an accurate fit between scintillation elements and photocathode windows, the entire series of scintillation 70 elements need not be rejected or mounted again, should one scintillation element become defective, for example, during mounting In each module, for example, 9 or 16 channels can again be accommodated However, it is alternatively 75 possible to choose a higher or lower number, even though the possibilities are limited if seamless connection as well as identical modules for detectors comprising scintillation elements to be read out on two sides and module rows situated 80 opposite each other are to be realized.
A detector in accordance with the invention is particularly suitable for use in a scanning X-ray examination device for medical diagnosis A device of this kind, comprising a detector 85 embodying the invention, is diagrammatically shown in Figure 6 A device of this kind comprises an X-ray source 70 for generating, for example, a flat fan-shaped X-ray beam 71 The aperture angle of the beam 71 is usually so large 90 that a part of a body 73 to be examined, situated on the supporting plate 72, is completely covered thereby After having passed through the body being examined, the intensity of the beam is locally measured by a detector 74 embodying the 95 invention The detector in this case comprises, for example 300 measuring channels, that is to say 300 different photocathodes with associated electron detectors The reading out from the detectors can be performed in conventional 100 manner as for known devices, it being possible to use substantially simpler and hence more reliable and cheaper electronic circuits in view of the higher internal intensification of the detectors.
For constructing a detector comprising a number 105 of detection cells, which number can be further extended until, for example, a circular detector is obtained, a comparatively large number of modules should still be combined To this end, use can be made of a modular system of assembly 110 as previously described, but it is alternatively possible to use a system comprising two slightly different, for example, mirror-symmetrical.
holders for the scintillation elements Identical modules or alternatively two different, preferably 115 mirror-symmetrical modules, can be added thereto For scanning the body to be examined, the X-ray source can be arranged to be rotatable around the body to be examined In known devices of this type the detector is usually moved 120 in synchronism during this rotation In order torealize this movement, the X-ray source is arranged to be rotatable in a support 76 by way of a movement mechanism 75.
The manufacture of the nitrided semi 125 conductor electron detector which can be used in the invention will now be described with reference to Figures 7 to 11 Starting material (see Figure 7) is an n-type silicon plate 80 having a resistivity of, for example, 7 Ohm cm On said 130 1 603271 plate an oxide layer 81, approximately O 5 micron thick, is provided by themal oxidation An annular slot 82 is etched in said oxide layer in a width of, for example, 30 microns and an outside diameter of 2 5 mm However, if desired, said annular slot may alternatively have a closed shape different from a circle and, for example, may be a square.
A layer 83 of polycrystalline silicon is then deposited in a thickness of approximately 0 5 micron for example, from an atmosphere containing Si H 4 and N, at 0 5 Torr and 6500 C, which layer 83 is then doped with boron, for example, by diffusion or ion implantation, after which during a further diffusion step the boron diffuses from the doped polycrystalline silicon into the silicon substrate 80 to form the annular p-type zone 84 The structure shown in Figure 7 is then obtained The zone 84 has a depth of 15-2 microns and a sheet resistance of approximately Ohms per square.
The polycrystalline silicon 83 is then given its ultimate shape in the usual manner by etching, after which the part of the oxide layer 81 situated within the zone 84 is removed by etching.
A 0 04 micron thick oxide layer 85 is then formed (see Figure 8) by thermal oxidation, on which an approximately 0 05 micron thick layer 86 of silicon nitride is deposited by deposition from an atmosphere containing Si H 4, NH 3 and H, at normal pressure at approximately 1050 ‘C.
Finally, a O 2 micron thick silicon oxide layer 87 is deposited hereon so that the structure shown in Figure 8 is obtained.
After removing layers formed on the lower side of the silicon plate 80 during the preceding operations a gettering step is carried out by heating in an atmosphere containing POC 1, at 10000 C succeeded by heating in nitrogen at 1050 TC for 1 hour A highly doped n-type layer 88 is obtained see Figure 9 Contact windows are then defined in the oxide layer 87 after which the nitride layer 86 is etched away within said windows The oxide layer 85 within the window is then etched away in a further etching step simultaneously with the oxide layer 87.
A thin p-type layer 89, see Figure 9 is formed by ion implantation of boron ions via the layers and 86 within the annular zone 84 The ion dosage is for example 4 10 I’ ions per cm’ the implantation energy is 35 Ke V After providing metal contacts 90 amd 91 for exmaple of aluminium on the N + type layer 88 and via the contact windows in the layers 85 and 86 on the polycrystalline silicon layer 83 the electron detector is ready for assembly.
As a modified embodiment of the described structure a groove may be etched in the silicon substrate 80 at the area of the slot 82 in the oxide layer 8 1 as isshown in Figure 10 Bysubsequently using the same operations as illustrated with reference to Figures 7 to 9 the structure shown in Figure 11 is obtained in which corresponding reference numerals are assigned to the components corresponding to those of Figures 7 to 9 The advantage of this structure is that X-ray radiation generated by electrons near the p-n junction between the layer 89 and the substrate 80 is absorbed by the metal layers 90 present in the groove so that they cannot penetrate into the oxide layer 81 and introduce a disturbing oxide charge there.
Claims (1)
WHAT WE CLAIM IS:-
1 A radiation detectorassembly forforming a plurality of adjacent individual radiation detectors in computed tomography apparatus, said assembly comprising scintillation means, and amplifying light detection means for detecting scintillation light produced in the scintillation means to provide a corresponding output, said light detection means comprising photoemissive means, optically coupled to said scintillation means and semiconductor-junction electrondetection means located in a vacuum chamber provided with an electron-optical system arranged so that electrons locally emitted by a respective photoemissive region in response to said scintillation light, are accelerated towards.
and generally concentrated at a corresponding semiconductor junction region to provide an individual output signal with photoemissive current amplification, wherein said scintillation means comprises a plurality of individual scintillation elements which are screened from one another with respect to scintillation radiation, each scintillation element being optically coupled to a corresponding photoemissive region forming a photocathode in a said electron-optical system.
2 A radiation detector assembly as claimed in Claim 1 wherein the electron-optical system is arranged to accelerate electrons emitted by a said photocathode to at least 10 Ke V.
3 A radiation detector assembly as claimed in Claim I or 2, wherein the semiconductor-junction electron-detection means comprises a block of semiconductor material having a Fermi gap of at least approximately 0 6 e V.
4 A radiation detector assembly as claimed in Claim 3 wherein the semiconductor material is provided with a protective surface layer formed by nitriding.
A radiation detector assembly as claimed in any one of Claims 1, 2, 3 and 4, wherein the electron detection means are provided respectively with a pn junction adjacent a surface which is remote from the electron entrance surface.
6 A radiation detector as claimed in any one of the preceding claims, wherein said amplifying light detection means includes a group of said photocathodes and electron detection means including associated said corresponding semiconductor junction regions accommodated in a housing, at least a part of said electron-optical system being common to said photocathodes.
7 A radiation detector assembly as claimed in Claim 6 wherein the housing includes a wall in which a corresponding plurality of windows are provided, each for a respective said photocathode.
8 A radiation detector assembly as claimed 1 603 271 in Claim 6 or 7, wherein an aperture diaphragm is located between the photocathodes and the electron detection means, said apertured diaphragm being provided with a respective comparatively small aperture adjacent each said corresponding semiconductor junction region.
9 A radiation detector assembly as claimed in any one of Claims 6, 7 and 8, wherein the wall on which the photocathodes are arranged is mad of glass having a comparatively high refractive index.
A radiation detector assembly as claimed in any one of the preceding claims, wherein said plurality of individual scintillation elements are arranged between two supporting plates to which a plurality of individual housings are demountablv connected each housing including a said light detection means for providing a respective group of said individual output signals.
11 A radiation detector assembly as claimed in Claim 10 wherein the individual scintillation elements are arranged in a single linear array, the corresponding scintillation light detection means being arranged in a plurality of adjacent linear arrays.
12 A radiation detector assembly as claimed in any one of the preceding claims, wherein the optical coupling between each said individual scintillation element and a window on which a said corresponding photocathode is located.
comprises a light-conductor.
13 A radiation detector assembly as claimed in any one of the preceding claims, wherein said plurality of individual scintillation elements is subdivided into groups which are respectively mounted on individual mounting supports to form sub-assemblies.
14 A radiation detector assembly as claimed in any one of the preceding claims, wherein a support for a said photocathode is formed by a read out face of a corresponding individual scintillation element.
A radiation detector assembly as claimed in any one of the preceding claims, wherein each individual scintillation element is shaped as an ellipsoid scintillation material being present adjacent one focal point and an entrance window of a light detection means being situated adjacent the other focal point.
16 A radiation detector assembly as claimed in any one of the preceding claims wherein said individual scintillation elements each contain scintillation material from the group of ceriumactivated yttrium phosphors.
17 A radiation detector assembly as claimed in any one of the preceding claims, formed as a plurality of distinct component assemblies which are mechanically coupled to one another in a demountable manner, each said component assembly comprising a light detection housing 60 having therein means for providing a group of said individual output signals, and an associated group of scintillation elements optically coupled to said light detection means in said housing.
18 A radiation detector assembly as claimed 65 in Claim 17, in which a said group of scintillation elements and associated mounting members form an assembly unit, the respective assembly units relating to adjacent component assemblies being mirror-symmetrical about a centre line extending 70 along the detector assembly from one component assembly to the next, the radiation detector assembly being formed by mechanically coupling adjacent mutually mirror-symmetrical assembly units to one another, mutually identical or 75 mutually mirror-symmetrically arranged said housings being respectively attached to said assembly units.
19 A radiation detector assembly as claimed in Claim 17 or 18, wherein a seamless transition 80 of the respectivce detection means is formed when the detector units are coupled.
A radiation detector assembly substantially as herein described with reference to the accompanying drawings 85 21 Computed tomography apparatus, including a radiation detector and an X-ray source for generating an X-ray beam which scans an object to be examined, wherein the radiation detector is a radiation detector assembly constructed in 90 accordance with any one of the preceding claims.
22 A method of manufacturing a radiation detector assembly as claimed in anyone of Claims I to 20, including during the formation of said photoemissive means by deposition of photo 95 cathode material, providing the electron detection means with a removable shield arranged to protect said electron detection means against contamination by alkali elements.
23 A method as claimed in Claim 22, in which 100 a barrier is located between the electron detection means and the photoemissive means and an aperture is formed in said barrier between each corresponding said semiconductor junction region and an associated said photocathode, and 105 said removable shield is formed by spheres which are arranged to close said apertures.
24 A method of manufacturing a radiation detectorassembly as claimed in any one of Claims I to 20, substantially as herein described with 110 reference to the accompanying drawings.
R J BOXALL, Chartered Patent Agent, Mullard Houe, Torrington Place, LONDON, WCIE 7 HD, Agent for the Applicants.
Printed for Her Majesty’s Stationery Office by MULTIPLEX techniques ltd, St Mary Cray, Kent 1981 Published at the Patent Office, 25 Southampton Buildings, London WC 2 l AY, from which copies may be obtained.
GB11665/78A
1977-03-28
1978-03-23
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NLAANVRAGE7703294,A
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RADIANT DETECTOR, AND ROENTGEN RESEARCH DEVICE CONTAINING THIS RADIANT DETECTOR.
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Philips Nv
DEVICE FOR DETERMINING LOCAL ABSORPTION VALUES IN A PLANE OF A BODY AND A ROW OF DETECTOR FOR SUCH DEVICE.
JPS5685328A
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*
1979-12-17
1981-07-11
Uni Pitsutsubaagu
Radioactive photographing apparatus
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1981-10-13
1983-04-16
Nippon Telegr & Teleph Corp
Electron beam emission type semiconductor diode
US5187369A
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1990-10-01
1993-02-16
General Electric Company
High sensitivity, high resolution, solid state x-ray imaging device with barrier layer
WO2003083010A1
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2002-03-28
2003-10-09
Hitachi Chemical Co.,Ltd.
Phosphor and phosphor composition containing the same
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2014-09-10
2019-03-06
キヤノン株式会社
Radiation imaging apparatus and radiation imaging system
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2020-01-09
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Image amplifier system
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Emi Ltd
Penetrating radiation examining apparatus having a scanning collimator
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High-voltage, low-background electronic camera
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Gamma camera
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LUMINOUS PHENOMENON LOCATION DEVICE
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1985-02-18
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1979-09-27
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1982-02-17
PS
Patent sealed [section 19, patents act 1949]
1985-11-20
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Patent ceased through non-payment of renewal fee
