X-ray radiographic method of recognition of materials and device for its realization

Abstract

An efficient X-ray radiographic method for recognition of materials of inspected objects and a corresponding device with improved functional possibilities are proposed, ensuring direct determination of the effective atomic number Z eff of the material, its density and thickness, as well as chemical composition. In customs inspection this should ensure practically unambiguous identification of explosives and drugs, and in medical tomography—early diagnostics of cancer tumors, osteoporosis, atherosclerosis and other dangerous and wide-spread diseases. The method includes X-raying of the inspected objects and recording of the transmitted radiation in several different spectral ranges with different effective energy by multi-element radiation receivers. For this purpose, quasimonochromatic X-ray radiation is used, and detection of radiation transmitted through the inspected object is made by spatially separated multi-element radiation receivers of selective sensitivity, upon each of which quasimonochromatic radiation of specified energy is directed. The background signal values in the absence of the inspected object are pre-recorded for each of said receiver elements under X-ray irradiation of specified energy, and signal values obtained in X-raying of a set of test objects are recorded. All the obtained signals are then normalized with respect to said background signals, and calibration constants are determined, after which the material is recognized by the obtained radiographic reflexes accounting for said calibration constants using special algorithms.

The invention claimed is: 
     
       1. An X-ray radiographic method of recognition of materials in an inspected object, comprising:
 transmitting radiation through the inspected object in a plurality of different spectral ranges with different effective energy, wherein X-ray radiation used is quasimonochromatic, 
 recording said radiation transmitted through the inspected object by spatially separated multi-element radiation receivers of selective sensitivity, upon each of which quasimonochromatic radiation of specified energy is directed, and 
 recognizing the materials in the inspected object, according to the following method:
 pre-recording background signal values in the absence of the inspected object for each of said receivers under X-ray irradiation of specified energy, 
 recording signal values obtained in X-raying of a set of test objects, 
 normalizing the signals are normalized signal values obtained in X-raying the set of test objects with respect to said background signals to determine calibration constants, and 
 recognizing the material by determining a radiographic reflex for the inspected object based on the recorded radiation normalized with respect to said background signals, and accounting for said calibration constants. 
 
 
     
     
       2. The X-ray radiographic method of recognition of materials of  claim 1 , wherein the X-ray radiation used comprises a plurality of beams of narrow quasimonochromatic radiation energy ranges, and each beam falls only onto a specified one of the radiation receivers. 
     
     
       3. The X-ray radiographic method of recognition of materials of  claim 1 , wherein relative concentrations of N materials in the inspected object are determined by employing at least M beams of narrow quasimonochromatic radiation energy ranges and by calculating separate calibration parameters for separate algorithms of material recognition for each material to be recognized, with M being equal to N. 
     
     
       4. The X-ray radiographic method of recognition of materials of  claim 2 , wherein the X-ray radiation used comprises a number of beams of narrow quasimonochromatic radiation energy ranges that is equal to twice the number of layers of the inspected object. 
     
     
       5. The X-ray radiographic method of recognition of materials of  claim 4 , wherein when the inspected object is homogeneous, the effective atomic number (Z eff ) of the inspected object is defined by the following equation: 
       
         
           
             
               
                 Z 
                 eff 
               
               = 
               
                 
                   
                     Z 
                     eff 
                   
                   ⁡ 
                   
                     ( 
                     
                       R 
                       _ 
                     
                     ) 
                   
                 
                 = 
                 
                   [ 
                   
                     
                       
                         
                           a 
                           ⁢ 
                           
                             R 
                             _ 
                           
                         
                         + 
                         b 
                       
                       
                         
                           c 
                           ⁢ 
                           
                             R 
                             _ 
                           
                         
                         + 
                         d 
                       
                     
                     ⁢ 
                     
                       [ 
                       
                         1 
                         / 
                         p 
                       
                     
                     ⁢ 
                     
                       
                         ; 
                         
                           
                             R 
                             _ 
                           
                           = 
                           
                             
                               R 
                               1 
                             
                             
                               R 
                               2 
                             
                           
                         
                       
                       , 
                     
                   
                 
               
             
           
         
       
       where R 1  is the radiographic reflex obtained at a first radiation energy range, R 2  is the radiographic reflex obtained at a second radiation energy range, a, b, c and d are the calibration constants determined by normalization of signal values obtained in X-raying the set of test objects, and p is a fitting parameter based on a level of the radiation energy ranges employed. 
     
     
       6. The X-ray radiographic method of recognition of materials of  claim 5 , wherein p is taken as 3 for radiation energy ranges less than 1 megaelectronvolt (MeV), and p is taken as 1 for radiation energy ranges greater than 1 MeV. 
     
     
       7. The X-ray radiographic method of recognition of materials of  claim 1 , wherein the set of test objects is chosen to include test objects having effective atomic numbers in the middle and at edges of a spectrum of expected effective atomic number values for the materials to be identified by the X-ray radiographic method. 
     
     
       8. The X-ray radiographic method of recognition of materials of  claim 7 , wherein the materials to be identified by the X-ray radiographic method involve separation of inorganics from organics. 
     
     
       9. The X-ray radiographic method of recognition of materials of  claim 8 , wherein the set of test objects includes wood as a low effective atomic number object, aluminum as a medium effective atomic number object, and iron as a high effective atomic number object. 
     
     
       10. The X-ray radiographic method of recognition of materials of  claim 7 , wherein the materials to be identified by the X-ray radiographic method involve recognition of organics. 
     
     
       11. The X-ray radiographic method of recognition of materials of  claim 10 , wherein the set of test objects includes multiple objects having effective atomic numbers in the range of 4 to 8. 
     
     
       12. The X-ray radiographic method of recognition of materials of  claim 1 , wherein an effective atomic number and a spatial density of the inspected object are obtained in order to recognize the materials therein. 
     
     
       13. An X-ray radiographic apparatus for recognition of materials in an inspected object, comprising:
 means for transmitting radiation through the inspected object in a plurality of different spectral ranges with different effective energy, wherein X-ray radiation used is quasimonochromatic,   means for recording said radiation transmitted through the inspected object by spatially separated multi-element radiation receivers of selective sensitivity, upon each of which quasimonochromatic radiation of specified energy is directed, and   means for recognizing the materials in the inspected object, including:
 means for pre-recording background signal values in the absence of the inspected object for each of said receivers under X-ray irradiation of specified energy, 
 means for recording signal values obtained in X-raying of a set of test objects, 
 means for normalizing the signal values obtained in X-raying the set of test objects with respect to said background signals to determine calibration constants, and 
 means for recognizing the material by determining a radiographic reflex for the inspected object based on the recorded radiation normalized with respect to said background signals, and accounting for said calibration constants. 
   
     
     
       14. The X-ray radiographic apparatus for recognition of materials in an inspected object according to claim 13, further comprising means for movement of the inspected object, wherein:
 the means for transmitting radiation through the inspected objected in a plurality of different spectral ranges comprises an X-ray emitter equipped by at least two monochromatic filters; and   the means for recording said radiation transmitted through the inspected objected and the means for recognizing the materials in the inspected object collectively comprise an X-ray radiation receiver comprising at least two spatially separated selectively sensitive detector arrays, random access memory, analog-to-digital converters, and video control device, wherein the at least two spatially separated selectively sensitive detector arrays have outputs connected to a joint analog-to-digital converter comprising a logarithmator with an output connected to a computer interface via software.   
     
     
       15. The apparatus of claim 14, wherein detectors of said selectively sensitive detector arrays for the energy range up to 20 keV are made of scintillators with effective atomic number below 25 and density less than 2.5 g/cm 3 , detectors for the energy range 20-45 keV are made up of scintillators with atomic number 25-45 and density 3-6 g/cm 3 , and detectors for the energy range 45-200 keV are made of scintillators with atomic number 45-80 and density not less than 6 g/cm 3 . 
     
     
       16. The apparatus of claim 15, wherein a thickness of said detectors is optimized for absorption of 70-90% of the incident radiation energy. 
     
     
       17. The apparatus of claim 15, wherein detectors of said selectively sensitive detector arrays for the energy range up to 20 keV are made of scintillators selected from the group consisting of p-terphenyl, silicon, germanium, ZnSe, ZnSe(Al,O), and ZnSe(O). 
     
     
       18. The apparatus of claim 15, wherein detectors of said selectively sensitive detector arrays for the energy range 20-45 keV are made of scintillators selected from the group consisting of A 2 B 6  compounds CdS(Te), and ZnSe(Te,O), and transparent ceramics Gd 2 O 2 S and ZnS. 
     
     
       19. The apparatus of claim 15, wherein detectors of said selectively sensitive detector arrays for the energy range 45-20 keV are made of scintillators selected from the group consisting of crystals CdTe, CsI(Tl), XWO, BGO, LSO and LPS. 
     
     
       20. The apparatus of claim 15, wherein detectors of said selectively sensitive detector arrays for the energy range up to 20 keV are made of crystal ZnSe(Al,O) of thickness up to 0.5 mm, detectors for the energy range 20-45 keV are made of crystal ZnSe(Te) of thickness up to 1.2 mm, and detectors for the energy range 45-200 keV are made of crystal CsI(Tl) of thickness up to 2 mm.