SCANNING METHOD AND APPARATUS

• US 20150241572A1
• Filed: 11/02/2012
• Published: 08/27/2015
• Est. Priority Date: 11/02/2011
• Status: Active Grant

• Current Assignee: Tracerco Ltd.
• Original Assignee: Johnson Matthey PLC
• Inventors: Jackson, Peter, James, Kenneth, Bowdon, Christopher, Featonby, Paul David, Howstan, James Stephen, Ronchi, Emanuele
• Granted Patent: US 9,897,558 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 2223/5055 scintillation crystal coupled to PMT
• CPC Class Codes: G01N 23/04 and forming images of the material
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]
• CPC Class Codes: G01N 23/06 and measuring the absorption
• CPC Class Codes: G01N 23/083 the radiation being X-rays
• CPC Class Codes: G01N 23/087 using polyenergetic X-rays
• CPC Class Codes: G01N 23/18 Investigating the presence of flaws defects or foreign matter
• CPC Class Codes: G01N 9/24 by observing the transmission of wave or particle radiation through the material
• CPC Class Codes: G01T 1/164 Scintigraphy
• CPC Class Codes: G01T 1/20182 Modular detectors, e.g. tiled scintillators or tiled photodiodes stacked detectors G01T1/20181
• CPC Class Codes: G01T 1/20185 Coupling means between the photodiode and the scintillator, e.g. optical couplings using adhesives with wavelength-shifting fibres
• CPC Class Codes: G01T 1/2019 Shielding against direct hits
• 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
• CPC Class Codes: G01V 5/226 using tomography
• CPC Class Codes: G21K 1/02 using diaphragms, collimators

Abstract

The invention discloses a scanning method and apparatus suitable for scanning a pipeline or process vessel in which a beam of gamma radiation from a source is emitted through the vessel to be detected by an array of detectors which are each collimated to detect radiation over a narrow angle relative to the width of the emitted radiation beam.

Claims

1. A method of scanning a structure to detect changes in density between different parts of the structure comprising the steps of:

a) providing at least one source of gamma radiation, and a plurality of detector units capable of detecting said gamma radiation, each said detector unit comprising;

i.a radiation detector comprising a scintillator comprising a scintillating material and having a detecting surface defined by its thickness t and height h, wherein t≦

h at the detecting surface and having a depth d perpendicular to the detecting surface at least 2t, and

ii.a photodetector for detecting light emitted by the scintillator in response to gamma radiation, and

iii.a collimator placed between the scintillator and the source of radiation;

b) causing said source unit to emit gamma radiation along a predetermined radiation path towards said detector, wherein said path passes through at least a portion of said structure;

c) measuring the number of photons of gamma radiation detected by each one of said detectors;

d) calculating a density value for each path from the measurement of photons detected by the detector associated with the respective path.

2. A method according to claim 1, wherein the plurality of detector units are arranged in close proximity to each other in the form of an arc having a radius centred on the centre of the structure to be scanned.

3. A method according to claim 1, wherein the source unit and detector units are mounted spaced apart on a support which provides means for at least a portion of the structure to be scanned to be located between the source unit and the detector units.

4. A method according to claim 1, wherein the source unit and detector units are rotated around the structure the radius of rotation having an origin within the structure.

5. A method according to claim 4, wherein guiding means are provided to guide said rotation in a predetermined path.

6. A method according to claim 5, wherein said guiding means is indexed.

7. A method according to claim 1 wherein 1 mm≦

t≦

5 mm, 10 mm≦

h≦

50 mm and 25 mm≦

d≦

75 mm.

8. A method according to claim 1 wherein the depth of the collimator of each detector unit is in the range from 50-150 mm.

9. A method according to claim 1, wherein the end of the collimator distal to the scintillator has an opening lying on the plane of a tangent to a circle having the source as its origin.

10. A method according to claim 1, wherein at least one of the collimators has at least one wall defining a channel which is aligned with a radius of a circle having the source as its origin.

11. A method according to claim 10, wherein each of the walls of the channel is aligned with a different radius of said circle and the opening of the channel is aligned to face directly towards the source.

12. A method according to claim 1, wherein said photodetector is mounted at an angle to the axis of the collimator and scintillator.

13. An apparatus for scanning a structure to detect changes in density between different parts of the structure comprising at least one source unit comprising a source of gamma radiation and shielding material arranged to restrict the emission of gamma radiation from the source unit:

a plurality of detector units capable of detecting said gamma radiation, each said detector unit comprising;

i. a radiation detector comprising a scintillator comprising a scintillating material and having a detecting surface defined by its thickness t and height h, wherein t≦

h at the detecting surface and having a depth d perpendicular to the detecting surface at least 2t, and

ii. a photodetector for detecting light emitted by the scintillator in response to gamma radiation, and

iii. a collimator placed between the scintillator and the source of radiation;

and data processing means for calculating a density value for each path from the measurement of photons detected by the detector associated with the respective path.

14. An apparatus according to claim 13, wherein said source unit and said detector units are mounted on a support in a fixed spaced apart relationship having means for rotating the source unit and detector units around an arc having an origin located between the source unit and detector units.

15. An apparatus according to claim 14, wherein said means comprises guiding means for guiding the rotation in a predetermined path.

16. An apparatus according to claim 15, wherein said guiding means comprise more than one portion which are movable to form a continuous guiding means.

17. An apparatus according to claim 13, wherein said collimator is formed, at least in part, from a first material having a first shielding capacity for gamma radiation, and a layer of a second material, having a greater shielding capacity than the first material, is positioned over at least one external surface of the detector unit.

18. An apparatus according to claim 13, wherein the plurality of detector units are arranged in close proximity to each other in the form of an arc having an origin located between the source unit and detector units.

19. An apparatus according to claim 13, wherein 1 mm≦

t≦

5 mm, 10 mm≦

h≦

50 mm and 25 mm≦

d≦

75 mm and the depth of the collimator of each detector unit is in the range from 50-150 mm.

20. An apparatus according to claim 13, wherein the end of the collimator distal to the scintillator has an opening lying on the plane of a tangent to a circle having the source as its origin.

21. An apparatus according to claim 13, wherein at least one of the collimators has at least one wall defining a channel which is aligned with a radius of a circle having the source as its origin.

22. An apparatus according to claim 21, wherein each of the walls of the channel is aligned with a different radius of said circle and the opening of the channel is aligned to face directly towards the source.

23. An apparatus according to claim 13, wherein said photodetector is mounted at an angle to the axis of the collimator and scintillator.