Method and apparatus for inspection of materials

• US 20080283761A1
• Filed: 05/16/2008
• Published: 11/20/2008
• Est. Priority Date: 05/17/2007
• Status: Active Grant

• Current Assignee: Kromek Limited (Kromek Group PLC)
• Original Assignee: Durham Scientific Crystals Limited
• Inventors: Robinson, Max, Basu, Arnab
• Granted Patent: US 7,693,261 B2
• Time in Patent Office: Days
• US Class Current: 250/370.09
• CPC Class Codes: G01N 23/04 and forming images of the material
• CPC Class Codes: G01N 23/2076 for spectrometry, i.e. using an analysing crystal, e.g. for measuring X-ray fluorescence spectrum of a sample with wavelength-dispersion, i.e. WDXFS
• CPC Class Codes: G01V 5/0016 Active interrogation, i.e. using an external radiation source, e.g. using pulsed, continuous or cosmic rays
• CPC Class Codes: G01V 5/22 Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays

Abstract

A method and apparatus for obtaining radiation transmission data including providing a radiation source, e.g., x-ray or gamma-ray source, and a radiation detector system, e.g., x-ray or gamma-ray detection system, spaced therefrom to define a scanning zone therebetween, the detector system capable of detecting and collecting spectroscopically resolvable information about incident radiation. Collecting a dataset of information about radiation incident including transmissivity of an object in the scanning zone at at least one scanning position from radiation transmitted through the object and received at the detector system. Resolving each dataset spectroscopically across a plurality of frequency bands within the spectrum of the source; at least one of the frequency bands corresponding to a characteristically scattered wavelength of a target species to be identified. The absence of or substantial reduction in a transmitted signal intensity at the frequency band is interpreted as the presence of the said target species.

Claims

1. A method of obtaining radiation transmission data of an object comprising the steps of:

providing a radiation source and a radiation detector system spaced therefrom to define a scanning zone therebetween, the detector system being capable of detecting and collecting spectroscopically resolvable information about incident radiation;

collecting a dataset of information about radiation incident at the detector and hence transmissivity of an object in the scanning zone at at least one scanning position from radiation transmitted through the object and received at the detector system; and

resolving each such dataset spectroscopically across a plurality of frequency bands within the spectrum of the source;

wherein at least one of the said plurality of frequency bands corresponds to a characteristically scattered wavelength of a target species to be identified, and wherein the absence of or substantial reduction in a transmitted signal intensity at the frequency band is interpreted as the presence of the said target species.

2. A method in accordance with claim 1 wherein at least one frequency band is allocated which corresponds to a characteristic first order Bragg scattering condition for a given target species.

3. A method in accordance with claim 1 wherein at least one frequency band is allocated which corresponds to a characteristic lower order Bragg scattering.

4. A method in accordance with claim 1 wherein a reduction in amplitude at a characteristic frequency band is determined numerically by comparison with the overall transmitted spectrum and/or by comparison with a known source spectrum and a result indicating the presence of the said target species is consequently generated.

5. A method in accordance with claim 1 wherein the dataset of information about radiation incidence collected at the detector is used to generate an image of an object in the scanning zone.

6. A method in accordance with claim 5 comprising the additional step of displaying a generated image or images.

7. A method in accordance with claim 5 wherein a succession of images is generated, and each such image is resolved spectroscopically across a plurality of frequency bands within the spectrum of the source, at least one of which corresponds to a characteristically scattered frequency of a target species, and at least one of which is used to generate an image.

8. A method in accordance with claim 7 wherein a plurality of frequency bands within the spectrum of the source are separately defined to correspond to a plurality of characteristic frequency bands, each corresponding to and containing within the band a characteristic scatter frequency of a given target species, and a further plurality of frequency bands within the source are allocated to generate a series of energy-differentiated images.

9. A method in accordance with claim 8 wherein the number of imaging frequency bands is between 2 and 10.

10. A method in accordance with claim 1 operating on the line-scan principle, comprising:

providing an x-ray source and an x-ray detector system spaced therefrom to define a scanning zone therebetween, the detector system comprising at least one linear array detector capable of generating spectroscopically resolvable information about incident x-rays;

causing an object to move relative to and through the scanning zone; and

resolving the resultant transmitted data.

11. An apparatus for scanning of and obtaining radiation transmission data from an object comprising:

a radiation source and a radiation detector system spaced therefrom to define a scanning zone therebetween and to collect in use a dataset of information about radiation incident at the detector and hence transmissivity of an object in the scanning zone at at least one scanning position;

a data processing apparatus to process and resolve each such dataset spectroscopically across a plurality of frequency bands within the spectrum of the source, wherein at least one of the said plurality of frequency bands corresponds to a characteristically scattered wavelength of a target species to be identified; and

a comparator to identify the absence of or substantial reduction in a transmitted signal intensity at the said frequency band and to output the same as an indication of the presence of the said target species.

12. An apparatus in accordance with claim 11 including a means to retain an object in and/or convey an object into and out of a scanning position.

13. An apparatus in accordance with claim 11 including an object handler to cause an object to move relative to and through the scanning zone in use.

14. An apparatus in accordance with claim 11 further including an image generation apparatus adapted co-operably with the detector to collect in use data for at least one image of an object in the scanning zone and to generate at least a first image from the output of the detector system.

15. An apparatus in accordance with claim 14 further including an image display means adapted to display at least the first image.

16. An apparatus in accordance with claim 11 wherein a detector is adapted to produce spectroscopic resolution in that it is fabricated from a material selected to exhibit inherently as a direct material property a direct variable electrical response to different parts of the x-ray spectrum.

17. An apparatus in accordance with claim 16 wherein the detector comprises a semiconductor material selected from a group consisting of cadmium telluride, cadmium zinc telluride (CZT), cadmium manganese telluride (CMT), germanium, lanthanum bromide, and thorium bromide.

18. An apparatus in accordance with claim 16 wherein the detector comprises a semiconductor material or materials formed as bulk crystal including a Group Il-VI semiconductor material.

19. An apparatus in accordance with claim 18 wherein the detector comprises a semiconductor material selected from a group consisting of cadmium telluride, cadmium zinc telluride (CZT), and cadmium manganese telluride (CMT).

20. An apparatus in accordance with claim 11 operating on the line-scan principle, comprising:

an x-ray source and an x-ray detector system spaced therefrom to define a scanning zone therebetween, the detector system comprising at least one linear array detector capable of generating spectroscopically resolvable information about incident x-rays.

21. An apparatus in accordance with claim 20 wherein the radiation source is a curtain beam x-ray source.