Scanning method and apparatus

1. A method of scanning a sub-sea pipeline to detect changes in density between different parts of the sub-sea pipeline, the method comprising:

providing at least one source of gamma radiation and a plurality of detector units configured to detect gamma radiation, each detector unit of the plurality of detector units 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,

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

iii. a collimator disposed between the scintillator and the at least one source of gamma radiation;

rotating the at least one source of gamma radiation and the plurality of detector units in a radius of rotation around an origin in the sub-sea pipeline;

providing a guiding system to guide said rotating in the radius of rotation around the origin in the sub-sea pipeline, the guiding system being indexed;

causing said at least one source of gamma radiation to emit gamma radiation along a plurality of predetermined radiation paths towards said plurality of detector units, the plurality of predetermined radiation paths passing through at least a portion of said sub-sea pipeline;

measuring a number of photons of gamma radiation detected by each one of said plurality of detector units; and

calculating a density value for each path from the number of photons of gamma radiation detected by each detector unit associated with the respective path.

2. The method according to claim 1 , wherein providing the at least one source of gamma radiation and the plurality of detector units comprises arranging the plurality of detector units in close proximity to each other in the form of an arc having a radius centered on the center of the sub-sea pipeline to be scanned.

3. The method according to claim 1 , wherein providing the at least one source of gamma radiation and the plurality of detector units comprises mounting the at least one source of gamma radiation and the plurality of detector units spaced apart on a support which provides a scanning device such that at least a portion of the sub-sea pipeline to be scanned is located between the at least one source of gamma radiation and the plurality of detector units.

4. The method according to claim 1 , wherein 1 mm≦t≦5 mm, 10 mm≦h≦50 mm, and 25 mm≦d≦75 mm.

5. The method according to claim 1 , wherein a depth of the collimator of each detector unit is in the range 50- 150 mm.

6. The method according to claim 1 , wherein an end of the collimator distal to the scintillator has an opening lying on the plane of a tangent to a circle having the at least one source of gamma radiation as its origin.

7. The method according to claim 1 , wherein the guiding system includes a motor and a mounting part on which the at least one source of gamma radiation and the plurality of detector units are mounted, the motor being configured to cause the at least one source of gamma radiation and the plurality of detector units to rotate.

8. A method of scanning a sub-sea pipeline to detect changes in density between different parts of the sub-sea pipeline, the method comprising:

providing at least one source of gamma radiation and a plurality of detector units configured to detect gamma radiation, each detector unit of the plurality of detector units 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,

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

iii. a collimator disposed between the scintillator and the at least one source of gamma radiation;

causing said at least one source of gamma radiation to emit gamma radiation along a plurality of predetermined radiation paths towards said plurality of detector units, the plurality of predetermined radiation paths passing through at least a portion of said sub-sea pipeline;

measuring a number of photons of gamma radiation detected by each one of said plurality of detector units; and

calculating a density value for each path from the number of photons of gamma radiation detected by each detector unit associated with the respective path,

wherein the collimator of at least one of the plurality of detector units has a plurality of walls defining a channel with an opening, each wall of the plurality of walls being aligned with a different radius of a circle having the at least one source of gamma radiation as its origin and the opening being aligned to face directly towards the at least one source of gamma radiation.

9. A method of scanning a sub-sea pipeline to detect changes in density between different parts of the sub-sea pipeline, the method comprising:

providing at least one source of gamma radiation and a plurality of detector units configured to detect gamma radiation, each detector unit of the plurality of detector units 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,

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

iii. a collimator disposed between the scintillator and the at least one source of gamma radiation;

causing said at least one source of gamma radiation to emit gamma radiation along a plurality of predetermined radiation paths towards said plurality of detector units, the plurality of predetermined radiation paths passing through at least a portion of said sub-sea pipeline;

measuring a number of photons of gamma radiation detected by each one of said plurality of detector units; and

calculating a density value for each path from the number of photons of gamma radiation detected by each detector unit associated with the respective path,

wherein providing the at least one source of gamma radiation and the plurality of detector units comprises mounting said photodetector at an angle to an axis of the collimator and the scintillator.

10. An apparatus for scanning a sub-sea pipeline to detect changes in density between different parts of the sub-sea pipeline, the apparatus comprising:

at least one source unit comprising a source of gamma radiation and shielding material configured to restrict an emission of gamma radiation from the at least one source unit;

a plurality of detector units configured to detect 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,

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

iii. a collimator placed between the scintillator and the at least one source unit;

a support, said at least one source unit and said plurality of detector units being mounted on the support in a fixed spaced apart relationship;

a scanning device configured to rotate the at least one source unit and the plurality of detector units around an arc having an origin located between the at least one source unit and the plurality of detector units, the scanning device comprising a guiding system configured to guide the rotation in a predetermined path, the guiding system comprising at least two portions that are movable to form a continuous guiding system; and

a data processor configured to calculate a density value for each path from photons of gamma radiation detected by each detector unit associated with the respective path.

11. The apparatus according to claim 10 , 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 at least one source unit and the plurality of detector units.

12. The apparatus according to claim 10 , wherein 1 mm≦t≦5 mm, 10 mm≦h≦50 mm, 25 mm≦d≦75 mm, and a depth of the collimator of each detector unit is in the range 50- 150 mm.

13. The apparatus according to claim 10 , wherein an end of the collimator distal to the scintillator has an opening lying on the plane of a tangent to a circle having the at least one source unit as its origin.

14. The apparatus according to claim 10 , wherein the guiding system includes a motor and a mounting part on which the at least one source of gamma radiation and the plurality of detector units are mounted, the motor being configured to cause the at least one source of gamma radiation and the plurality of detector units to rotate.

15. An apparatus for scanning a sub-sea pipeline to detect changes in density between different parts of the sub-sea pipeline, the apparatus comprising:

at least one source unit comprising a source of gamma radiation and shielding material configured to restrict an emission of gamma radiation from the at least one source unit;

a plurality of detector units configured to detect 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,

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

iii. a collimator placed between the scintillator and the at least one source unit; and

a data processor configured to calculate a density value for each path from photons of gamma radiation detected by each detector unit associated with the respective path,

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, and is positioned over at least one external surface of each detector unit.

16. An apparatus for scanning a sub-sea pipeline to detect changes in density between different parts of the sub-sea pipeline, the apparatus comprising:

at least one source unit comprising a source of gamma radiation and shielding material configured to restrict an emission of gamma radiation from the at least one source unit;

a plurality of detector units configured to detect 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,

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

iii. a collimator placed between the scintillator and the at least one source unit; and

a data processor configured to calculate a density value for each path from photons of gamma radiation detected by each detector unit associated with the respective path,

wherein at least one of the collimators has a plurality of walls defining a channel with an opening, each wall of the plurality of walls being aligned with a different radius of a circle having the at least one source unit as its origin and the opening being aligned to face directly towards the at least one source unit.

17. An apparatus for scanning a sub-sea pipeline to detect changes in density between different parts of the sub-sea pipeline, the apparatus comprising:

at least one source unit comprising a source of gamma radiation and shielding material configured to restrict an emission of gamma radiation from the at least one source unit;

a plurality of detector units configured to detect 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,

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

iii. a collimator placed between the scintillator and the at least one source unit; and

a data processor configured to calculate a density value for each path from photons of gamma radiation detected by each detector unit associated with the respective path,

wherein said photodetector is mounted at an angle to an axis of the collimator and the scintillator.